Category 6™

March Rainfall Records Doused; Damaging Freeze Possible in Northeast

By: Bob Henson , 6:03 PM GMT on March 31, 2016

More severe weather is in store for Thursday and Friday after tornadoes hopscotched near and east of Tulsa on Wednesday and flooding rains inundated other areas. A damage survey was underway in northeast Oklahoma on Thursday morning in the wake of the tornadoes, which caused at least seven injuries and damaged a number of structures. One of the twisters was visible from Tulsa International Airport (see video here, from Twitter user Brandyn). In its roundup of severe weather reports from Wednesday, NOAA’s Storm Prediction Center (SPC) listed four preliminary tornado reports from the storm near Tulsa, along with two other reports from southeast Kansas and southeast Arkansas.

The greatest threat for severe weather Thursday afternoon and evening is across northern Mississippi, northwest Alabama, and western Tennessee, where the 11:30 am CDT outlook from SPC is calling for an enhanced risk of severe weather (Figure 1). An outflow boundary from previous storms is stretched east-west across northern MS and AL. As upper-level energy approaches, this boundary will serve to enhance vertical wind shear, and a strong tornado or two could develop in supercells that form near the boundary. The upper-level trough and associated cold front will slide across the central Gulf Coast on Friday, leading to a continued risk of severe weather in that area--primarily high winds and large hail, together with heavy rain. Severe storms are also possible northward along the cold front to the mid-Atlantic, particularly in the Piedmont of Virginia and North Carolina if temperatures warm enough there on Friday.

Figure 1. The convective outlooks issued by NOAA’s Storm Prediction Center late Wednesday morning, March 30, 2016, included an enhanced risk area for Wednesday centered on northern Mississippi and a slight risk for Thursday near the central Gulf Coast.

Figure 2. A tornado touches down in the vicinity of Tulsa, OK, on Wednesday, March 30, 2016. Image credit: AP Photo/Larry Papke.

Wettest March on record for Memphis, Little Rock
Today’s rains will serve as a capstone to a March that already ranks among the wettest on record for states bordering the lower Mississippi River. As of midnight Wednesday night, Memphis, TN, was sitting at 13.78” for the month. This already beats the previous March record of 13.04” from the region’s devastating spring of 1927, which brought the worst river flood in our nation’s history. Memphis records go back to 1872. In Little Rock, AR, an even 4.00” on Wednesday led to widespread flooding across the area. Little Rock has now racked up its wettest March by far since records began in 1875, with 12.22” this month beating out 10.43” (1897). Both Memphis and Little Rock will have added to their March totals before the day and month are done; Memphis will go up by at least 2.00” based on rains that had already fallen by midday Thursday.

Figure 3. Temperatures projected from this morning’s 12Z Thursday run of the GFS model for 12Z (7:00 am CDT) Tuesday, April 5, 2016. Image credit: Levi Cowan,

Widespread freeze damage possible next week across East
Early April may bring a cruel surprise to many trees and shrubs that popped into premature bloom over the last several weeks across the Northeast. It finally dipped below freezing on Wednesday morning in Baltimore and in areas just west of I-95. However, from New York southward, it’s still been nearly a month since most of the urban corridor has seen a hard freeze. In New York and Philadelphia, the last temperature below 32°F was back on March 5, although Central Park touched 32° on March 20 and 21. During the 1981-2010 climatological period, the average date for the final reading of 31°F or colder in Central Park was on March 13. Making matters worse--though it seemed pleasant enough at the time--was the spell of record-smashing mid-March warmth that sent temperatures into the low 80s in parts of New York and New England.

The lack of snow cover over the Northeast has allowed soil temperatures to warm as well, which hastens the budding and blooming of trees. The mildness has advanced New Jersey’s growing season by several weeks, state climatologist David Robinson (Rutgers University) told AgWeb. Plum and peach trees in the Lehigh Valley of Pennsylvania were already in bloom this week. In Washington, D.C., the famed yoshino cherry blossoms of the Tidal Basin hit peak bloom on March 25, almost two weeks before the April 4 average and earlier than in all recent years, with the notable exceptions of 2012 (March 20) and 1990 (March 15).

Figure 4. Temperatures across the entire nation except for the Pacific Northwest coast were well above average for the period March 1 – 29, 2016. Image credit: NOAA/NWS/CPC.

Several rounds of cold weather are on tap for the mid-Atlantic and Northeast over the next few days. Temperatures may dip to near freezing from D.C. northward on Sunday morning, with colder readings well into the 20s possible across much of the area by midweek (see Figure 3 above), and perhaps again by next weekend. Although these readings are 20°F to 30°F below average, they’re unlikely to set very many record lows: the latest 32°F temperatures on record are April 29 in Washington, May 11 in Baltimore and Philadelphia, and May 6 in Central Park. However, the impacts of the coming cooldown may be more akin to getting a freeze in mid- to late April, given the advanced state of plant growth over the region. The situation brings to mind the disastrous freeze of April 11-12, 2012, which followed the unprecedented Great Warm Wave of March. That freeze, together with frosts later that month, devastated already-blooming fruit trees across the Midwest and Northeast. In Michigan, the apple crop was virtually wiped out.

WU weather historian Christopher Burt has a new blog post summarizing where California stands in terms of snowpack and precipitation after a not-quite-miraculous March.

Bob Henson

Figure 5. Dogwood blossoms on Wednesday, March 30, 2016, in Danville, VA. Image credit: wunderphotographer WeatherWise.

Flood Extreme Weather Severe Weather Tornado

A 50-Day Heat Wave Forecast, and the Future of Subseasonal to Seasonal Prediction

By: Bob Henson , 6:50 PM GMT on March 29, 2016

For those of us interested in the future of long-range weather forecasting, two developments this week pair very nicely. A paper published on Monday online in the journal Nature Geoscience shows how heat waves across the midwestern and eastern U.S. may be predictable with some skill as far as 50 days out. On its heels is the Tuesday release of a report from the U.S. National Academies, Next Generation Earth System Prediction: Strategies for Subseasonal to Seasonal Forecasts. The report argues that there is great potential to improve the quality and value of forecasts in the two-week to 12-month range, if the necessary resources can be marshaled--and if researchers can develop and tailor products designed to fit the needs of users.

The Pacific Extreme Pattern: A prelude to big heat in the central and eastern U.S.
The paper in Nature Geoscience--led by Karen McKinnon, a postdoctoral researcher at the National Center for Atmospheric Research--finds that a particular arrangement of sea surface temperature (SST) can take shape across the North Pacific weeks ahead of the advent of widespread summer heat over much of the central and eastern U.S. This oceanic configuration, dubbed the Pacific Extreme Pattern (PEP), features colder-than-usual SSTs along the west coast of North America, with a warmer-than-usual area north of Hawaii and another cold anomaly toward Japan (Figure 1).

The PEP bears some of the hallmarks of the negative (cold) phase of the Pacific Decadal Oscillation, which is known to raise the odds of drought and heat across parts of the United States. However, the PDO and PEP are separate beasts, according to McKinnon. “PEP has a smaller spatial scale and varies more within a season than the PDO,” said McKinnon in an email. “While in some cases SST anomalies may project similarly onto both patterns, we do not believe that they are generally the same phenomenon.”

Figure 1. Colored areas show anomalies (departures from average) in sea surface temperature associated with the Pacific Extreme Pattern (PEP) at the 40-day lead time, when it would suggest an enhanced risk of heat 40 days later over the central and eastern U.S. Overlaid in dashed and solid black contours are the Pacific Decadal Oscillation (PDO). While a negative PDO is defined by a large warm anomaly that spans most of the North Pacific (solid contours), with a cold tongue near the western U.S. (dashed contours), the PEP has a large cold anomaly in the western part of the ocean basin (blue colors), a smaller warm anomaly in the middle part of the basin, and then a second cold anomaly in the eastern part of the basin. Image credit: Karen McKinnon, NCAR.

Figure 2. The five clusters of stations across the U.S. identified as tending to experience hot days at the same time. The cluster examined in this study (blue stations] covers much of the central and eastern U.S. Image credit: Fig. S1(a) from K.A. McKinnon et al., Long-lead predictions of eastern United States hot days from Pacific sea surface temperatures, published online on March 28, 2016, in Nature Geoscience.

By exploring where unusually hot U.S. summer temperatures tend to cluster, the study team decided to focus on a large and important region extending from the Central Plains and encompassing most of the nation east of the Mississippi River and north of Florida (see Figure 2). As the PEP evolves in a sequence of steps identified by the authors, it tends to generate high pressure off the West Coast and, further downstream, dry, hot weather over the central and eastern U.S. On a regional basis, the paper defines a hot day as one where at least 5% of the study area (at least 80 of 1613 weather stations) experiences a high of at least 6.5°C (11.7°F) above average (one standard deviation). Using this yardstick, the evolution of the PEP provides significant skill at predicting the timing of hot days for the region as a whole up to 50 days in advance. Even at the individual-station level, the PEP demonstrates significant skill at about half of all locations out to 40 days, particularly across the Mississippi Valley.

Figure 3. SST anomalies in the North Pacific Ocean 50 days in advance of June 29, 2012. The pattern inside the green box best matches the early stage of the Pacific Extreme Pattern, indicating that there would be an increase in the odds of a heat wave in the eastern half of the United States at the end of June. Temperatures on June 29 (bottom) largely bore out the forecast, with readings above 100°F covering much of the Central Plains and mid-Mississippi Valley. Image credit: Karen McKinnon, NCAR.

Hints in May of heat in July
The authors make their case further through a retroactive “hindcast” of the scorching U.S. summer of 2012, which produced record heat and grinding drought across much of the study domain. The three biggest multi-day summer heat spikes of 2012 began on June 25, July 16, and 29 July. The state of the PEP on May 15 corresponded to a more-than-threefold increase in the likelihood of hot days 40 days later (June 24). At the end of May, the PEP indicated even stronger 40-day odds for a hot period around July 9.

Clearly, the PEP is not a perfect predictor, but it may serve as an useful new avenue toward probabilistic heat and drought forecasts over a key part of the U.S., with more specific timing than now offered by today’s leading techniques. “The Pacific Extreme Pattern appears to provide a cohesive framework for improving seasonal prediction of summer precipitation deficits and high temperature anomalies in the eastern U.S.” the paper asserts. “The identification of predictive skill at a seven-week lead time is an important advance over current seasonal forecast models that tend to under-predict the probability of extremes.” It’s possible that the PEP is associated with one or more factors that also influence eastern U.S. heat and dryness. The authors add that “it would be useful to better determine whether the ocean forces, feed backs on, or simply acts as a passive recorder of atmospheric anomalies in the months preceding hot weather.”

Dr. Todd Crawford, chief meteorologist at The Weather Company, said: “These results confirm the importance of North Pacific SST patterns in modulating summer temperature patterns over the US on seasonal time scales, and for the first time suggest predictability of extreme heat events on sub-seasonal time scales.  There is now the potential for the addition of another useful statistical forecasting technique to accompany dynamical model output in the sub-seasonal forecaster's toolbox.” Crawford, whose TWC Energy group carries out seasonal and sub-seasonal prediction for a range of customers, told me he’s being “peppered with client questions/comments” about the paper.

Going operational (experimentally)
We’ll soon find out how well this new technique works in real time. Based on daily PEP calculations, McKinnon and colleagues are planning to make predictions for this summer, beginning in early May. These forecasts will be available through a link to be posted at McKinnon’s website. “Our hope is that these can be used directly by, e.g., city leaders to ensure that enough cooling rooms are available for those without air conditioning if there are increased odds of a heat wave, and utility companies who may want to make sure they have sufficient power to bring online in case of spikes in electricity demand,” McKinnon told me. “We also hope to interface with operational and seasonal forecasters to see if the information from PEP could complement that provided by the current dynamical models.”

Figure 4. Leniel Fields of K&K Maintenance wipes his face in the heat as he trims and maintains the grounds at the Franklin School Apartments near downtown St. Louis on July 23, 2012. The city hit 106°F that day, with temperatures remaining above 80°F at night for three consecutive days. Image credit: AP Photo/St. Louis Post-Dispatch, Erik M. Lunsford.

A comprehensive strategy for improving forecasts up to a year out
The PEP study is one step in a direction encouraged by the National Academies report released on Tuesday. This report serves as an update to a similarly themed 2010 study, Assessment of Intraseasonal to Interannual Climate Prediction and Predictability, this time dropping the multi-year component and focusing on the interval from two weeks to 12 months in advance, a period dubbed S2S (seasonal to subseasonal). Another new tack is broadening the kinds of phenomena that might be predicted, encompassing extreme weather events such as the heat waves analyzed in the new paper above. The study examines recent progress in using such phenomena as the Madden-Julian Oscillation and the North Atlantic Oscillation as forecasting tools, along with such efforts as the North American Multi-Model Ensemble. “However, an associated U.S. national research agenda aimed at strengthening the contributions of S2S forecasts to public and private activities has not yet emerged,” the report noted.

The study’s vision--that “S2S forecasts will be as widely used a decade from now as weather forecasts are today”--includes 16 recommendations to get us there, as well as four research strategies:

• Engage users in the process of developing S2S forecast products
• Increase S2S forecast skill
• Improve prediction of extreme and disruptive events and consequences of unanticipated forcing events
• Include more components of the Earth system in S2S forecast models

“It is easy to envision the potential value of high-quality predictions two weeks to 12 months ahead for any number of industries--for example, energy, water resource management, and agriculture,” noted committee chair Raymond Ban (Ban and Associates) in the report’s preface. “Even if such information never matches the level of confidence associated with tomorrow’s weather forecast, it could still be used by individuals, businesses, and governments to plan and make a large array of important decisions.”

Figure 5. Severe-weather risk areas for Wednesday (left) and Thursday (right), March 30 and 31, 2016, as designated by NOAA’s Storm Prediction Center on Tuesday morning, March 29.

Tornadoes may spin up across Central/Southern Plains on Wednesday
We’ll be back with a new post by Thursday at the latest. We’re also keeping an eye on a fairly classic set-up for early-spring severe weather in the nation’s midsection, especially from around Kansas City to the Dallas-Fort Worth area. At midday Tuesday, NOAA’s Storm Prediction Center was calling for a slight risk of severe weather on Wednesday over much of the southern and central Great Plains, shifting on Thursday into the central Gulf Coast area. The chance of a major tornado outbreak did not appear large, given the moderate amounts of instability expected and a tendency toward southwest winds at most levels, which would tend to reduce vertical wind shear. Early-morning storms on Wednesday may also cut back on daytime heating. Still, it’s late March, and all of the ingredients should be present for the full gamut of severe weather, including tornadoes in some areas. SPC noted in its Tuesday update that the risk for Wednesday could be upgraded in subsequent outlooks.

Bob Henson

Long-Range Forecasting Extreme Weather Heat Drought

Longest Coral Bleaching Event on Record Continues to Hammer Reefs

By: Bob HEnson , 3:30 PM GMT on March 28, 2016

Even as the El Niño of 2015-16 winds down, coral reefs remain threatened by the longest episode of global-scale bleaching on record. NOAA announced in October 2015 that the third global bleaching event had begun, with reefs from the Florida Keys to Fiji suffering widespread damage over the past year. In February, NOAA scientists announced that the bleaching event was the longest on record. The event is a result of widespread ocean warming related to long-term climate change as well as regional warmings triggered by El Niño, which began in early 2015. The prolonged nature of the bleaching event is especially worrisome because it allows for multiple years of damage during seasonal peaks in upper-ocean temperature, giving the reefs less time to recover. “We may be looking at a 2- to 2½-year-long event,” said Mark Eakin, coordinator of NOAA’s Coral Reef Watch program. “Some areas have already seen bleaching two years in a row.”

In its 2015 annual summary of conditions across U.S. coral reefs, issued on March 7, 2016, NOAA projected that the global bleaching event will likely extend into 2017. Since 2014, the report noted, 100% of all U.S. coral reef areas have experienced at least some level of thermal stress associated with unusually warm waters, with 41% experiencing Alert Level 2 thermal stress (typically associated with widespread bleaching and mortality). Record-breaking events occurred in 2015 near Hawaii, American Samoa, the Northern Mariana Islands, and Florida. Reefs near Hawaii were hard hit by bleaching in both 2014 and 2015.

Figure 1. Bleached coral at Lizard Island, north of Cooktown, Australia, captured by the XL Catlin Seaview Survey in March 2016. The global insurance firm XL Catlin is working with scientific institutions around the world to carry out the ongoing survey, which has collected more than 700,000 panoramic images along nearly one million kilometers. Image credit: XL Catlin Seaview Survey, via

Major damage at Great Barrier Reef
Severe bleaching is now under way across the northern reaches of the Great Barrier Reef, which is a UNESCO World Heritage Site and one of the world’s great treasuries of marine diversity. At some reefs off far northeast Australia near the tip of Cape York, up to 50 percent of coral have already died. The Great Barrier Reef Marine Park Authority classified the unfolding event as Level R3, the most dire, because of severe regional bleaching over the last few days. (R3 can also be triggered if less-severe bleaching is particularly widespread.) “To put it in simple, stark terms, multiple areas of the reef are now dead and dying,” said David Suggett (University of Technology Sydney) in a Conversation essay published last week. South of the hardest-hit area, clouds and heavy rain had tamped down ocean temperatures and reduced the extent of bleaching, according to a March 21 update from the park authority.

“The damage this year seems more localized but much more intense than 1998 and 2002,” Justin Marshall (University of Queensland) told me in an email, referring to past events across the Great Barrier Reef. The focus toward the north this year, he said, is “likely due to [an] unfortunate stack of factors there—the south got more wind and rain for a bit, and that seems to have shielded it a bit.” Marshall is chief investigator of Coral Watch, a nonprofit that fosters public awareness and entrains students, visitors, and others in helping to monitor and protect the reefs.

After conducting an aerial survey north of Cairns that extended some 600 kilometers (270 miles), veteran researcher Terry Hughes (James Cook University) saw evidence of severe bleaching across all but four of the 520 reefs surveyed. Hughes told Australia’s ABC News that he expects roughly half of the bleached coral across the northern Great Barrier Reef to die over the next month. This week his group plans to extend the surveys southward toward Townsville. “How many 100s of reefs blitzed?” he wondered aloud in a tweet, after calling last week’s expedition “the saddest reef trip of my life.” Both Hughes and Marshall are interviewed in this ABC video.

Figure 2. High-alert areas for coral bleaching across the Pacific Ocean for the week beginning March 26, 2016, based on satellite-derived sea surface temperature data. The areas currently at highest risk are concentrated along and south of the Equator, as upper-ocean temperatures are now close to their seasonal peak in the Southern Hemisphere. In addition, warmer-than-usual waters directly related to El Niño have enhanced the risk in the central and eastern equatorial Pacific. Image credit: NOAA Coral Reef Watch

Figure 3. The sequence of events involved in coral bleaching. Image credit: Great Barrier Reef Marine Park Authority.

How warm water damages reefs
Bleaching is a sure sign of a coral reef in trouble. The brilliant colors associated with coral reefs are produced not only by the reefs themselves (which are animals related to jellyfish or sea anemone) but also by the microscopic algae called zooxanthellae that coexist with the reefs. As the coral send polyps upward and outward from their hard skeletons (Figure 3), the zooxanthellae lodged in the coral tissue carry out photosynthesis and provide nutrients to the coral. In return, the coral provides shelter and carbon dioxide to the algae. Because the algae need sunlight to photosynthesize, coral reefs are located just below the ocean surface in warm tropical and subtropical waters. Stresses such as unusually high water temperatures, increased water acidity, or pollution can disturb the symbiotic relationship between the corals and the algae that live inside them. If water temperatures are more than 1-2°C above their typical warm-season highs for an extended period, the algae may began to photosynthesize too quickly for the coral to handle. To protect its own tissue, the coral may expel the algae, and the grayish-white skeletons of the coral become visible through the now-translucent tissue of the polyps. The more severe and prolonged the bleaching, the more difficult it is for the reef to recover.

Third time is no charm
The global bleaching that struck during and after the “super” El Niño of 1997-98 was a shocker--the first global-scale mass bleaching ever recorded. Although the world’s oceans had been gradually warming for decades, the 1997-98 El Niño was the first time that large sections of coral were exposed to temperatures warm enough to cause extensive bleaching. Some 16% of the world’s reefs died as a result of this mass bleaching. It was followed in 2010 by the second mass global bleaching, again triggered by El Niño on top of long-term warming. About a third of all carbon dioxide emitted by human activity goes into the oceans, where it can degrade coral in another way. Coral growth rates in the Great Barrier Reef have dropped by some 40% in the last 40 years, apparently in large part due to the acidifying influence of human-produced carbon dioxide absorbed by the oceans.

Less than a thousandth of the ocean floor is covered by reefs, but these areas play host to a spectacular variety of life--an estimated quarter of all marine species known to exist--and they help support the ocean-based livelihoods of half a billion people. Reefs are under a variety of threats in addition to long-term human-caused warming, including diseases and overfishing. In the Caribbean alone, surveys indicate that reef habitats have declined by more than 50% since the 1970s. While some types of coral may be able to grow upward quickly enough to keep up with modest sea level rise, not all species will be able to adapt to fast-warming temperatures. We may end up seeing a few hardy coral species proliferate in our warming climate, while many others, including some of the most delicate and beautiful creatures on Earth, struggle--and sometimes fail--to adapt to our new and evolving normal. An interesting article by Meehan Crist in The Atlantic touches on some of the efforts being made to preserve and strengthen reefs and the ecosystems they support, including the development of artificial reefs.

We’ll have a new post by Tuesday afternoon.

Bob Henson   

Figure 4. Departures from the 1971-2000 seasonal average in sea surface temperature for February 1998 (top) and February 2016 (bottom), just after the peaks of the “super” El Niño events of 1997-98 and 2015-16. Image credit: IRI

Climate Change Coral Reefs Air and Water Pollution

Here Comes La Niña--Or Does It? What History, Models, and Experts Tell Us

By: Bob Henson , 4:28 PM GMT on March 25, 2016

After a superheated few months, the tropical Pacific is starting to cool down, one of several signs that the memorable El Niño event of 2015-16 is nearing its end. The looming question is whether this blockbuster will be followed by a sequel--which, like most sequels, could pale in comparison--or whether La Niña is waiting in the wings, ready to take the stage for what could be an extended run.

It’s not hard to find evidence of El Niño in decline. Sea surface temperatures (SSTs) are steadily dropping in and around the benchmark Niño3.4 region and elsewhere over the central and eastern tropical Pacific (Figure 1). After peaking at 3.1°C above average in late November 2015--the highest weekly value on record--the Niño3.4 SSTs were down to 1.7°C above average last week. Other indicators suggest that El Niño is hanging on by its fingernails. Beneath the veneer of warm SSTs, subsurface waters throughout the tropical Pacific have grown increasingly cooler (Figure 2).

Figure 1. Weekly anomalies (departures from seasonal average) in sea surface temperatures for the period March 13-19, 2016. Warm anomalies persisted over the central and eastern tropical Pacific, although less impressive than at their peak several months ago. Image credit: NOAA/ESRL/PSD.

Figure 2. Vertical cross section of temperatures (top) and anomalies (bottom) across the equatorial Pacific Ocean for the period March 19-23, 2016. Cooler-than-average waters now dominate the top 200 meters (600 feet) of the equatorial Pacific, although the surface layer remains warm. Image credit: TAO Project Office, NOAA/PMEL.

During a strong El Niño event, trade winds weaken, and recurrent periods of westerly wind help push warm water toward the eastern tropical Pacific. Surface winds averaged over a five-day period are now blowing from east to west across the entire tropical Pacific, a sign of rejuvenated trades.

All these indicators line up nicely with the classic mode of decay found in other strong El Niños of the past few decades. According to the official monthly outlook from NOAA’s Climate Prediction Center, issued on March 10, “A transition to ENSO-neutral is likely during late Northern Hemisphere spring or early summer 2016.” What’s less certain is what will happen after the Pacific enters a neutral state, assuming that it does.

“I’m going to say there’s a 99.9% chance we see El Niño conditions break down by this summer,” Michael Ventrice (The Weather Company) told me in an email. All of the five analog years since 1950 analyzed by Ventrice and colleagues bring the Pacific into neutral territory (Niño3.4 SSTs within 0.5°C of the seasonal average) by later in the year. Forecast models are in near-universal agreement that neutral conditions will prevail by this summer, and it looks increasingly likely that the tropical Pacific will continue cooling, with La Niña conditions possible by autumn. However, there’s just enough uncertainty to keep forecasters sweating it out.

Springtime obscures the crystal ball
What’s known as the spring predictability barrier makes this the toughest time of the year to anticipate how the El Niño–Southern Oscillation (ENSO) will behave. ENSO refers to the coupled atmosphere-ocean process that swings between El Niño and La Niña. About half of the time, neutral conditions prevail, with El Niño and La Niña roughly splitting the other 50% of the time. El Niños have been more frequent overall in recent decades, but La Niñas are more likely to recur for two or three years in a row.

Figure 3. El Niño and La Niña events since 1950, as defined by the Oceanic Niño Index, which tracks the events through three-month rolling averages of sea surface temperatures across the Niño3.4 region of the eastern tropical Pacific. “Very strong” or “super” El Niño events are those where at least one three-month average is at least 2.0°C above normal. Image credit: Jan Null, Golden Gate Weather Services, using data from NOAA (see the link for a larger version of this graphic).

In tandem with the seasonal cycle across the tropical Pacific, both El Niño and La Niña tend to strengthen toward the end of a calendar year and weaken during the first half of the next year. Thus, it’s easier to project the evolution of an El Niño or La Niña event as it’s taking shape, during the northern fall, than to anticipate what will emerge by the next fall.

Figure 4 (below) demonstrates the spring predictability barrier in all its glory. After being tightly clustered for the next couple of months, the various models diverge drastically by the coming autumn. If there’s a consensus, it’s for a weak La Niña to emerge by the latter half of the year. Several models have a moderately strong La Niña in place as soon as late summer, while a couple of other models bring back El Niño for a return visit by late 2016. It turns out that at least two of the models favoring El Niño (the CCSM4 and CFSv2 models, seen in Figure 4) were being swayed by an implausibly cold Atlantic--the type of initialization problem where unrealistic starting-point data can lead to unorthodox model behavior down the line. As Figure 4 shows, the LDEO model favors El Niño more strongly than any other, and that model is a fairly simple Pacific-only model without any Atlantic initialization.

Update: NOAA is announcing on Friday that an adjustment to the initialization system used for CCSM4 and CFSv2 is being implemented on Monday, addressing the cold bias in the Atlantic Ocean. Importantly, when it tested this adjustment, NOAA found a major shift: "the long-lead forecasts evolved from the current El Niño event into neutral or La Niña conditions during the next 9 months in the Nino3.4 SST plumes." Here's a NOAA technical briefing on the results. The NOAA/CPC outlook issued last week, which factored in the model initialization concerns, called for a roughly 50% chance of La Niña conditions by fall. I wouldn't be surprised to see those odds going up in April.

Figure 4. Projections of various forecast models for the evolution of SSTs in the Niño3.4 region over the next few months. These forecasts were compiled and released in mid-March. El Niño is in place when SSTs are at least 0.5°C above average for five overlapping three-month periods. La Niña is defined the same way, except that SSTs are below rather than above average. The bottom axis shows abbreviations for three-month intervals (e.g., JJA is June-July-August). Image credit: International Research Institute for Climate and Society.

The classic, but not guaranteed, hand-off from El Niño to La Niña
Our physical understanding of ENSO suggests that the models calling for La Niña may indeed be on the right track. Veteran researcher Anthony Barnston (International Research Institute for Climate and Society, or IRI) lays out the science behind the “delayed oscillator theory” in an easy-to-digest ENSO Blog entry from last January. In a nutshell, strong El Niño events trigger two competing forces: eastward-moving features called oceanic Kelvin waves, which straddle the equatorial Pacific, and westward-moving Rossby waves, located on either side of the equator. Passing each other like ships in the night, the Kelvin waves reinforce El Niño, while the Rossby waves head toward Indonesia and then bounce back eastward. At that point, months after their creation, they can lead to subsurface cooling that eventually shifts the system from El Niño toward La Niña.

One might expect that the stronger the El Niño, the stronger the Rossby waves that help lead to its demise. Indeed, Barnston shows that during the NOAA-favored period of most reliable records (1950 to today), stronger El Niño events tend to correlate with cooler SSTs a year later. The strongest events in this NOAA dataset are the “super” El Niño events of 1997-98 and 1982-83, along with a close runner-up, 1972-73. All three were followed by La Niña conditions a year later. (The cooling in 1983-84 was too brief to qualify as a La Niña event, but it was followed by a bona fide La Niña in 1984-85.) Out of the ten moderate or stronger El Niños analyzed by Barnston, six were followed by La Niña conditions a year later—but two were followed by neutrality, and the other two saw a redevelopment of weak to moderate El Niño conditions.

Figure 5. Scatterplot showing the relationship in ENSO states from one year to the next, for every year since 1950 in which an El Niño occurred. Each dot represents a pair of “year 1 vs. year 2” ENSO states. In general, the stronger the El Niño (higher values on the x-axis), the stronger the subsequent La Niña (lower values on the y-axis). The ENSO states here are drawn from Niño3.4 SSTs (the Oceanic Niño Index) for the six overlapping three-month periods from August-October to January-March. Data are not completely in for 2015-16, but this future dot should end up close to 2.0°C on the x axis, which implies that La Niña is historically likely in 2016-17. For more details and a larger version of the graphic, see the associated ENSO Blog post by Anthony Barnston published on Jan. 28, 2016. Image credit: NOAA, courtesy Anthony Barnston.

Forward into the past
WU member Eric Webb (North Carolina State University, @webberweather) has been digging even further back into El Niño history. Over the last few months, Webb has been refining his own Ensemble Oceanic NINO Index, a product that draws on 26 long-term datasets and analyses created by institutions around the world. Stretching back to 1865, Webb’s index identifies “super” El Niños in 1877-78 and 1888-89 as well as 1972-73 (deemed “super” in Webb’s index), 1982-83, and 1997-98. One motivation behind incorporating multiple datasets is to help alleviate some of the issues with older data that have led NOAA/CPC to focus on the post-1950 period in its own analyses, including the historical ENSO dataset shown in Figure 3. Webb has also been working on a confidence index that assesses how well five leading ENSO definitions agree from period to period.

With the help of Webb’s index, the argument for La Niña in 2016-17 gets even stronger. All five of Webb’s “super” events were followed by La Niña events that lasted two to three years. Yet none of the eight strong El Niño events that fell below the “super” threshold (1896-97, 1902-03, 1965-66, 1991-92, 1957-58, 1940-41, 1987-88, and 1930-31) produced multiyear La Niña events. “In fact, many weren't even followed by a La Nina in the subsequent year,” Webb told me. “This is a very intriguing statistic, and it likely highlights the role for properly initializing ENSO intensity with respect to forecasting its behavior beyond the spring predictability barrier, much less a year or two in advance. This also provides a potential future avenue of research for assessing its behavior in specific ENSO scenarios.”

Although Webb’s work has yet to be peer-reviewed, it points in the same direction as other research: a powerful tendency for big La Niñas to follow big El Niños. “Eric’s statement sounds quite reasonable to me,” said IRI’s Barnston. “I don’t think any expert could disagree with it. Given the inherent limit of predictability, there may not be very good low-hanging fruit, but it doesn’t hurt to keep trying.”

The case for El Niño
“A transition to La Niña is not a done deal,” according to Klaus Wolter (NOAA Earth System Research Laboratory). Wolter and colleague Michael Timlin (Midwestern Regional Climate Center) developed the Multivariate ENSO Index (MEI), which employs both oceanic and atmospheric variables and goes back to 1871, providing yet another perspective. In a 2011 paper, Wolter and Timlin found a close relationship between the strength and longevity of La Niña events. The picture gets a bit more complex for El Niño: “super” events typically last 12 to 18 months, while other strong events have actually persisted for more than two years. “I find it interesting that 1930-31, 40-41, and 1991-92 [all strong El Niño years] were followed by long-lived El Niño conditions,” Wolter said in an email.

One more wrinkle to consider is the Pacific Decadal Oscillation. As we discussed early last year, El Niño events become more likely when the PDO is in its positive mode, which was the case in the 1980s and 1990s. Now that the PDO has been consistently positive for more than two years, we may have entered a longer-term positive mode, which would favor El Niño more often than La Niña.

The upshot: While current observations show El Niño decaying, and the strength of the 2015-16 event argues for a good chance of La Niña in 2016-17 (conceivably lasting more than a year), it’s still a bit too soon to entirely rule out a repeat visit from El Niño later this year.

Figure 6. The Atlantic hurricane seasons that followed the two most recent “super” El Niño events (1982-83 and 1997-98) are a study in contrasts. The 1983 season (left) was the quietest post-1970 Atlantic season on record in terms of accumulated cyclone energy, with only 4 named storms and 3 hurricanes. The 1998 season (right) produced 14 named storms, 10 hurricanes, and more than $3 billion in damage, as well as the catastrophic Hurricane Mitch, which killed more than 10,000 people as it decayed over Central America.

Implications for the 2016 Atlantic hurricane season
It’s well established that El Niño years tend to suppress tropical cyclone action in the North Atlantic, due to increased upper-level wind shear and other factors, while La Niña tends to favor above-average activity in the North Atlantic. Timing makes a big difference: if a transition to La Niña happens late in the year, it’s less likely to influence the Atlantic hurricane season. The forecast team at Colorado State University led by Phil Klotzbach and William Gray will issue their first outlook for the 2016 Atlantic season on April 14. Klotzbach stresses another key factor now in play alongside El Niño and La Niña--the recent apparent switch toward a cool mode of the Atlantic Multidecadal Oscillation (AMO), which we’ll be discussing in a future post. Here’s what Klotzbach had to say when I asked him about the AMO and other factors leading into the 2016 season:

“The far North Atlantic has been quite cold for about three years now. This cold anomaly especially stands out at present, given how warm the remainder of the globe is due in part to the strong El Niño. When the far North Atlantic is cold, it tends to force wind and pressure patterns that then cool the tropical Atlantic. We've seen a significant cooling of the eastern subtropical Atlantic in recent weeks [see Figure 7 below], and there is the potential that these cold anomalies could propagate into the tropical Atlantic for the peak of the Atlantic hurricane season. If this occurs, there is the potential that the hurricane season may not be particularly active.”

We’ll be back with our next post on Monday. In the meantime, have a great weekend, everyone!

Bob Henson

Figure 7. Trend in sea-surface temperatures across the eastern tropical Atlantic for early March 2016 as compared to January 2016. Image credit: NOAA/ESRL/PSD, courtesy Phil Klotzbach.

El Niño La Niña ENSO

Fire and Ice on the Plains: Intense Snow, Raging Blazes

By: Bob Henson , 3:09 PM GMT on March 24, 2016

A tightly wrapped storm system produced a wild array of weather-related impacts over the Great Plains and Midwest on Wednesday, including paralyzing snowfall, severe thunderstorms, and a massive prairie fire. The most widespread problems occurred with late-season snowfall that stretched along a frontal zone from the Colorado Rockies northeast more than 1,000 miles to Michigan. Dubbed Winter Storm Selene by the Weather Channel, the heavy snow and high winds knocked out power to thousands of residents. Snow totals of a foot or more were reported in Iowa, Minnesota, South Dakota, Wisconsin, and Wyoming, according to TWC, with 31.6” falling near the mountain town of Pinecliff, CO.

Figure 1. A lone pedestrian trudges along the westbound lanes of Speer Boulevard in downtown Denver as a spring storm packing high winds and wet, heavy snow blankets the city early Wednesday, March 23, 2016. Image credit: AP Photo/David Zalubowski.

Figure 2. An unidentified exotic creature took shape on the railing of my deck at the height of the snowstorm on Wednesday, March 23, 2016. Image credit: Bob Henson.

Snowstruck: A first-hand report
One of the hardest-hit areas was my own neck of the woods, the Denver-Boulder area. As late as Monday night, most computer forecast models had been distinctly lukewarm about the chance of major snow in the populous Front Range corridor, adjoining the Rockies. The classic scenario for big snow here is for an upper-level storm to move slowly from the Four Corners region across southern Colorado, forcing strong, deep upslope flow against the Front Range mountains. Models were on target in projecting that Wednesday’s storm would crank up just east of the Front Range, a setup that often produces blizzard conditions east of the Denver area. As it happened, the storm intensified just close enough to the Front Range to push blizzard conditions into much of the urban corridor, along with extremely heavy snowfall rates that peaked as high as 4”/hour. High-resolution short-range models fell into agreement on this trend Tuesday evening, just a few hours before the storm hit full force.

Roads and yards were still wet at my place in Louisville (just east of Boulder) when the snow began around 2 AM Wednesday. By 9 AM, there was almost a foot of snow on the ground. By the time the storm was wrapping up, around 1 PM, I measured a phenomenal 21” accumulation—all of it having fallen in just 10 hours! Similar readings between 20” and 25” were observed in a swath from just east of Boulder across the north and east Denver suburbs, as well as in many of the often-hard-hit foothills locations to our west. Interstates were closed throughout the region for hours, as was Denver International Airport.

El Niño gives big snow a boost in northeast Colorado
The odds of a big winter storm go up considerably in the Boulder area during El Niño events. An informal study by Boulder cooperative observer Matt Kelsch (University Corporation for Atmospheric Research) found that, since 1950, nearly half of the Boulder snowstorms measuring at least 15” occurred during El Niño. Less than 20% happened during La Niña.

Figure 3. A old train trestle bridge burns near Lake City, KS, on Wednesday, March 23, 2016. The bridge was set afire by a large grass fire burning in Barber County, KS. Lake City is about 15 miles northwest of Medicine Lodge, where at least two homes were destroyed by fire. Image credit: Travis Morisse/The Hutchinson News via AP.

Figure 4. The hourly Air Quality Index briefly reached the “unhealthy for sensitive groups” level (orange) across part of south-central Kansas at 8:00 pm CDT Wednesday, March 23, 2016, as particulate matter from a massive grass fire blew into the area. Image credit:, data courtesy of Kansas Department of Health and Environment.

Fierce fire spreads from Oklahoma to Kansas
To the south of the big snow, warm, bone-dry air and powerful southwest winds gusting above 60 mph kicked off a number of grass fires, including one gargantuan fire that crossed the Oklahoma-Kansas border. In less than 48 hours, this fire tore across a swath estimated by the Oklahoma Forestry Service as spanning an immense 400,000 acres (625 square miles). The fire sent a pall of smoke over much of southern Kansas, including the Wichita area (see Figure 4). At least two homes were destroyed in Medicine Lodge, KS, and the town of 2000 residents was under a voluntary evacuation. With the fire still out of control late Wednesday, Kansas governor Sam Brownback declared a state of disaster. Hundreds of firefighters were reportedly working on Thursday morning along a 30- to 40-mile-long fire line. The fire’s cause is under investigation. NOAA’s Storm Prediction Center (SPC) had warned of extreme fire risk from southeast New Mexico to eastern Kansas on Wednesday. A WU station at Medicine Lodge reported wind gusts of 51 mph on Wednesday afternoon as the relative humidity dipped below 10%.

Figure 5. VIIRS view of the state of Kansas (outlined) at 1946Z (2:46 pm CDT) on Wednesday, March 23, 2016. Thick cloudiness in northwest Kansas is associated with heavy snow, while the streaks of smoke at center are being produced by major grass fires near the KS/OK border. Image credit: USDA Forest Service/Remote Sensing Applications Center.

Figure 6. A MODIS view of the western two-thirds of Kansas at 1948Z (2:48 pm CDT) on Wednesday, March 23, 2016. False color is used to highlight areas of cold cloud tops (top left) and wildfire (bottom center). Image credit: USDA Forest Service/Remote Sensing Applications Center.

Severe weather possible across South on Thursday
A line of severe thunderstorms erupted Wednesday evening ahead of a dry line, with some of the most intense storms extending roughly from Tulsa, OK, to Dallas-Fort Worth, TX. No tornadoes were reported, and there were only a few reports of thunderstorm-related high wind, but large hail up to golf-ball size was widespread. (Update: Storm surveys on Thursday confirmed three tornadoes from Wednesday, one each in Arkansas, Texas, and Missouri.) Another round of severe storms is possible on Thursday from central Kentucky and Tennessee into parts of Mississippi, Alabama, and Georgia, where NOAA/SPC outlined a slight risk of severe weather in its initial Day 1 outlook for Thursday. Wind damage is a particular concern with any squall lines or line segments that emerge. Instability could be somewhat higher across the mid-South late this weekend as another upper-level storm approaches the region. SPC’s long-range convective outlook is calling for a potential risk of severe weather on Sunday, centered on western Kentucky and Tennessee.

We’ll be back with our next post on Friday.

Bob Henson

Fire Winter Weather Extreme Weather Severe Weather

World Meteorological Day: A Hotter, Drier, Wetter World of Weather

By: Bob Henson , 10:37 PM GMT on March 23, 2016

Today is World Meteorological Day, held each year on the date (March 23, 1950) when the treaty creating the World Meteorological Organization went into force. The theme of this year’s World Meteorological Day is a timely one: “Hotter, Drier, Wetter—Face the Future.” Dozens of billion-dollar weather disasters plagued our planet in 2015—many of them involving droughts and floods—and inflicted a total $123 billion in damage (see Figure 1, below). That total came in below the 15-year average of $175 billion. However, the pain was widely distributed in the form of 29 separate billion-dollar disasters, the fourth largest number since accounting began in 1990, according to insurance broker Aon Benfield.

While the economic toll from heat waves occurs largely in the form of agricultural losses related to drought, heat waves also pose a direct risk to human health. A severe pre-monsoonal heat wave took an estimated 2500 lives in India during May 2015, making it the nation’s second deadliest heat wave on record and the fifth deadliest in world records compiled by EM-DAT.

Human-produced climate change is already hiking the odds of the three weather trends highlighted by the WMO. Heat extremes are on the rise both nationally (see photos below) and globally. In many parts of the world, the heaviest precipitation events (such as the top 1% of one-day totals) are becoming even heavier. And when drought strikes, the impact is exacerbated by a warmer atmosphere, which allows more moisture to escape from parched soils and drying lakes; in turn, the ever-drier ground allows temperatures to soar even further. This year’s World Meteorological Day theme reminds us, as does a recent report from the National Academies, that the climate of our future is related to the weather events that we deal with every day.

Bob Henson

Figure 1. (below) The 29 billion-dollar global weather disasters, adjusted for inflation, as compiled by insurance broker Aon Benfield in their Annual Global Climate and Catastrophe Reports. There are several more U.S. severe-weather events in the list than are shown in the accompanying map, due to space constraints: Image credit: Lauren Moyer/WU.

Climate Change

Avoiding a Soylent Green Future by 2040; First Severe Outbreak of Spring Coming

By: Jeff Masters and Bob Henson , 12:51 PM GMT on March 23, 2016

If you want a sobering look at a potential global apocalyptic food shortage scenario, you don’t need to rent a copy of the 1973 sci-fi classic, “Soylent Green”. A non-sci-fi computer model being developed by the Global Sustainability Institute at the UK's Anglia Ruskin University predicts that catastrophic food shortages, triggered by a combination of climate change, water scarcity, energy crisis, and political instability might lead to a virtual collapse of industrial civilization by 2040. The model explores short-term scenarios of policy decisions by simulating social-economical-environmental systems, including the impact of climate-induced drought on crop failures and food prices. The model was successfully used to simulate the multiple factors--including the great Russian drought of 2010--that made the 2011 Arab Spring uprisings more likely. These uprisings caused major unrest in at least twelve nations, and forced rulers from power in Tunisia, Egypt, Libya, and Yemen. Dr. Aled Jones, director of the Global Sustainability Institute, said this in a June 2015 interview with Insurge Intelligence about their model:

"We ran the model forward to the year 2040, along a business-as-usual trajectory based on ‘do-nothing’ trends—that is, without any feedback loops that would change the underlying trend. The results show that based on plausible climate trends, and a total failure to change course, the global food supply system would face catastrophic losses, and an unprecedented epidemic of food riots. In this scenario, global society essentially collapses as food production falls permanently short of consumption."

Figure 1. Food riot from the sci-fi classic, “Soylent Green”.

Figure 2. Tunisians carrying loaves of bread protest high food prices and confront riot police during a demonstration against the country's new government in Tunis on January 18, 2011. Riot police fired tear gas and dispersed the rally. Global food prices spiked in late 2010 and early 2011, leading to widespread unrest and the "Arab Spring" in northern Africa and the Middle East, toppling the governments of four nations. The high food prices were primarily due to Russia's great heat wave and drought in the summer of 2010, which decimated the Russian wheat crop. Image credit: MARTIN BUREAU/AFP/Getty Images.

The good news
The good news is this is a short-term model, and was not designed to run for a period of decades. With the world now committed to de-carbonize its economy as a result of the December 2015 Paris Accord, long-term changes to the global food system are in store, making a “Soylent Green” world less likely than the model might suggest (although there is no telling what the future holds for the trendy, lab-concocted Soylent beverage). According to an October 2015 report by the World Bank, Future of Food: Shaping A Climate-Smart Global Food System, a growing and diverse spectrum of practices called "Climate Smart Agriculture" are showing it is possible to simultaneously deliver higher agricultural productivity, greater climate resilience, and lower greenhouse gas emissions. Important among these are silvo-pastoral livestock systems (blending forests and pastures; "silva" is Latin for forest), agroforestry, intercropping, diversification of production systems toward less water- and emission-intensive crops, improved pasture management, better fertilizer use, minimum tillage, alternative wetting and drying of rice, biogas production from agricultural waste products/livestock manure, improved irrigation and drainage efficiency that includes lowering emissions by reducing energy consumption of pumping stations, and reducing food loss and waste. For example, Uruguay has quadrupled its agricultural production within a decade while significantly reducing greenhouse gas emissions per unit of food production by using some of these techniques. Of course, making these changes will cost money, but the report notes that rates of return to public investment in agricultural research and extension have been very high, averaging at least 40 percent in recent decades. We really have no choice but to make massive changes and investments in the global food system if we want to avoid the fate of the many civilizations and nations that have collapsed because of drought.

Springtime's first severe weather episode is brewing
The nation's first multi-day round of severe weather since the spring equinox will take shape from late Wednesday into Thursday (see Figure 3). A seasonably strong upper-level trough will move across the south-central and southeastern states, pulling up modest amounts of Gulf moisture. The richest moisture has been scoured out of the Gulf by earlier fronts, so instability will be less than impressive, and wind shear in the lowest levels will also be on the weak side. Still, enough total vertical wind shear will be on hand to support a slight risk of severe thunderstorms from northeast Texas to western Illinois by Wednesday evening. Storms will redevelop across the South on Thursday, perhaps extending northward into the Ohio Valley. Damaging winds and hail are the main threat on both days, but a few tornadoes are possible.

Figure 3. Severe weather outlooks for Wednesday, March 23, 2016 (left) and Thursday, March 24 (right), issued by NOAA's Storm Prediction Center late Tuesday night.

As of Monday, March 21, NOAA's Storm Prediction Center had received 202 preliminary tornado reports for the year to date, slightly above the 11-year average (2005-2015) of 184 preliminary tornado reports for the period Jan 1 - Mar 21. Tornado activity and high-wind reports surged last month with the deadly mid-Atlantic outbreak of February 24. The main story in March has been hail--in particular, a destructive hailstorm that pounded the Fort Worth, TX, area on Thursday morning, March 17. The Insurance Council of Texas estimates that insured damages from this storm will top $600 million. That would make it one of the top-20 costliest weather disasters in Texas history. The heavy weather struck the Dallas-Fort Worth region just before and after sunrise, which is one of the least common times of day to get damaging hail in this region.

Jeff Masters (food shock); Bob Henson (severe weather)

Drought Climate Change Severe Weather

Ten Civilizations or Nations That Collapsed From Drought

By: Jeff Masters , 3:15 PM GMT on March 21, 2016

Drought is the great enemy of human civilization. Drought deprives us of the two things necessary to sustain life--food and water. When the rains stop and the soil dries up, cities die and civilizations collapse, as people abandon lands no longer able to supply them with the food and water they need to live. While the fall of a great empire is usually due to a complex set of causes, drought has often been identified as the primary culprit or a significant contributing factor in a surprising number of such collapses. Drought experts Justin Sheffield and Eric Wood of Princeton, in their 2011 book, Drought, identify more than ten civilizations, cultures and nations that probably collapsed, in part, because of drought. As we mark World Water Day on March 22, we should not grow overconfident that our current global civilization is immune from our old nemesis--particularly in light of the fact that a hotter climate due to global warming will make droughts more intense and impacts more severe. So, presented here is a "top ten" list of drought's great power over some of the mightiest civilizations in world history--presented chronologically.

Collapse #1. The Akkadian Empire in Syria, 2334 BC - 2193 BC. In Mesopotamia 4200 years ago, the great Akkadian Empire united all the indigenous Akkadian-speaking Semites and the Sumerian speakers, and controlled Mesopotamia, the Levant, and parts of Iran, sending military expeditions as far south as present-day Oman. In a 2000 article published in Geology, "Climate change and the collapse of the Akkadian empire: Evidence from the deep sea", a team of researchers led by Heidi Cullen studied deposits of continental dust blown into the Gulf of Oman in the late 1990s. They discovered a large increase in dust 4200 years ago that likely coincided with a 100-year drought that brought a 30% decline in precipitation to Syria. The drought, called the 4.2 kiloyear event, is thought to have been caused by cooler sea surface temperatures in the North Atlantic. The 4.2 kiloyear event has also been linked to the collapse of the Old Kingdom in Egypt (see below). The paper concluded, "Geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between Mesopotamian aridification and social collapse, implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the Akkadian empire." In this image, we see Stele of Narâm-Sîn, king of the Akkadian Empire, celebrating his victory against the Lullubi from Zagros. Limestone, c. 2250 BC, Louvre Museum. Image credit: Marie-Lan Nguyen.

Collapse #2. The Old Kingdom of ancient Egypt, 4200 years ago. The same drought that brought down the Akkadian empire in Syria severely shrank the normal floods on the Nile River in ancient Egypt. Without regular floods to fertilize the fields, poor harvests led to reduced tax income and insufficient funds to finance the pharaoh's government, hastening the collapse of Egypt's pyramid-building Old Kingdom. An inscription on the tomb of Ankhtifi during the collapse describes the pitiful state of the country when famine stalked the land: "the whole country has become like locusts going in search of food…" In this image, we see two great structures from the Old Kingdom: The Pyramid of Khafre and the Great Sphinx of Giza. Image credit: wunderphotographer Jeff41.

Collapse #3. The Late Bronze Age (LBA) civilization in the Eastern Mediterranean. About 3200 years ago, the Eastern Mediterranean hosted some of the world’s most advanced civilizations. The Mycenaean culture was flourishing in Greece and Crete. The chariot-riding Hittites had carved out a vast empire encompassing a large part of Asia Minor and the Middle East. In Egypt, the New Kingdom was at its height. However, around 1200 BC, these Eastern Mediterranean civilizations declined or collapsed. According to a 2013 study in PLOS, studying grains of fossilized pollen shows that this collapse coincided with the onset of a 300-year drought event. This climate shift caused crop failures and famine, which "precipitated or hastened socio-economic crises and forced regional human migrations at the end of the LBA in the Eastern Mediterranean and southwest Asia." In this image, we see the fall of Troy (complete with the famed Trojan Horse), an event recounted in Greek mythology at the end of the Bronze Age, as represented by the 17th century painter Kerstiaen De Keuninck. Image credit: Wikipedia Commons.

Collapse #4. The Maya civilization of 250 - 900 AD in Mexico. Severe drought killed millions of Maya people due to famine and lack of water, and initiated a cascade of internal collapses that destroyed their civilization at the peak of their cultural development, between 750 - 900 AD. Haug, G.H. et al., in their 2003 paper in Science, "Climate and the collapse of Maya civilization," documented substantial multi-year droughts coinciding with the collapse of the Maya civilization. In this image, we see the Mayan ruins at Xunantunich. Image credit: wunderphotographer novembergale.

Collapse #5. The Tang Dynasty in China, 700 - 907 AD. At the same time as the Mayan collapse, China was also experiencing the collapse of its ruling empire, the Tang Dynasty. Dynastic changes in China often occurred because of popular uprisings during crop failure and famine associated with drought. The Tang dynasty--a golden age of literature and art in Chinese civilization--began to weaken in the eighth century, and it fully collapsed in 907 AD. Sediments from Lake Huguang Maar in China dated to the time of the collapse of the Tang Dynasty indicate a sudden and sustained decline in summertime monsoon rainfall. Agriculture in China depends upon the summer monsoon, which supplies about 70% of the year's rain in just a few months. A 2007 article in Nature by Yancheva et al. speculated that "migrations in the tropical rain belt could have contributed to the simultaneous declines of both the Tang dynasty in China and the Classic Maya in Central America." In this image, we see the world's largest sitting Buddah, the 71-metre (234-feet) tall Leshan Giant Bubbha, built in 713 AD in the Chinese Tang Dynasty, in China's southwestern city of Leshan, in Sichuan province. Image credit: Liu Jin/AFP/Getty Images.

Collapse 6. The Tiwanaku Empire of Bolivia's Lake Titicaca region, 300 - 1000 AD. The Tiwanaku Empire was one of the most important South American civilizations prior to the Inca Empire. After dominating the region for 500 years, the Tiwanaku Empire ended abruptly between 1000 - 1100 AD, following a drying of the region, as measured by ice accumulation in the Quelccaya Ice Cap, Peru. Sediment cores from nearby Lake Titicaca document a 10-meter drop in lake level at this time. In this image, we see tourists exploring the Tiwanaku archaeological site in Tiahuanaco, Bolivia. Image credit: AIZAR RALDES/AFP/Getty Images.

Collapse 7. The Ancestral Puebloan (Anasazi) culture in the Southwest U.S. in the 11th - 12th centuries AD. Beginning in 1150 AD, North America experienced a 300-year drought called the Great Drought. This drought has often been cited as a primary cause of the collapse of the ancestral Puebloan (formally called Anasazi) civilization in the Southwest U.S., and abandonment of places like the Cliff Palace at Mesa Verde National Park in Colorado. The Mississippian culture, a mound-building Native American civilization that flourished in what is now the Midwestern, Eastern, and Southeastern United States, also collapsed at this time. Cliff Palace image credit: wunderphotographer Amtnspirit.

Collapse #8. The Khmer Empire based in Angkor, Cambodia, 802 - 1431 AD. The Khmer Empire ruled Southeast Asia for over 600 years, but was done in by a series of intense decades-long droughts interspersed with intense monsoons in the fourteenth and fifteenth centuries that, in combination with other factors, contributed to the empire's demise. The climatic evidence comes from a seven-and-a-half century reconstruction from tropical southern Vietnamese tree rings presented in a 2010 study by Buckley et al., "Climate as a contributing factor in the demise of Angkor, Cambodia". They wrote: "The Angkor droughts were of a duration and severity that would have impacted the sprawling city’s water supply and agricultural productivity, while high-magnitude monsoon years damaged its water control infrastructure." In this image, we see the ruins of Baphuon, a temple-mountain dedicated to the Hindu God Shiva in Angkor. Image credit: Jean-Pierre Dalbéra.

Collapse #9. The Ming Dynasty in China, 1368 - 1644 AD. China's Ming Dynasty--one of the greatest eras of orderly government and social stability in human history--collapsed at a time when the most severe drought in the region in over 4000 years was occurring, according to sediments from Lake Huguang Maar analyzed in a 2007 article in Nature by Yancheva et al. Drought experts Justin Sheffield and Eric Wood of Princeton, in their 2011 book, Drought, speculated that a weakened summer monsoon driven by warm El Niño conditions in the Eastern Pacific was responsible for the intense drought, which led to widespread famine. An inscription found carved on a wall of Dayu Cave in the Qinling Mountains of Central China dated July 10, 1596, during the 24th year of the MIng Dynasty's Emperor Wanli, said: Mountains are crying due to drought." In the image above, we see another inscription on the wall of the same cave from a much later drought in 1891. It reads: "On May 24th, 17th year of the Emperor Guangxu period (June 30th, 1891 CE), Qing Dynasty, the local mayor, Huaizong Zhu led more than 200 people into the cave to get water. A fortuneteller named Zhenrong Ran prayed for rain during a ceremony." Image credit: L. Tan.

Collapse #10. Modern Syria. Syria's devastating civil war that began in March 2011 has killed over 300,000 people, displaced at least 7.6 million, and created an additional 4.2 million refugees. While the causes of the war are complex, a key contributing factor was the nation's devastating drought that began in 1998. The drought brought Syria's most severe set of crop failures in recorded history, which forced millions of people to migrate from rural areas into cities, where conflict erupted. This drought was almost certainly Syria's worst in the past 500 years (98% chance), and likely the worst for at least the past 900 years (89% chance), according to a 2016 tree ring study by Cook et al., "Spatiotemporal drought variability in the Mediterranean over the last 900 years." Human-caused emissions of greenhouse gases were "a key attributable factor" in the drying up of wintertime precipitation in the Mediterranean region, including Syria, in recent decades, as discussed in a NOAA press release that accompanied a 2011 paper by Hoerling et al., On the Increased Frequency of Mediterranean Drought. A 2016 paper by drought expert Colin Kelley showed that the influence of human greenhouse gas emissions had made recent drought in the region 2 - 3 times more likely. Wunderground's climate change blogger, Dr. Ricky Rood, has his take on the current drought in Syria in his March 21 post, Ineffective Resolution: Middle East and Climate Change. In this image, we see Kurdish Syrian girls among destroyed buildings in the Syrian Kurdish town of Kobane on March 22, 2015. Image credit: Yasin Akgul/AFP/Getty Images.

Buckley, B.M. et al., 2010, "Climate as a contributing factor in the demise of Angkor, Cambodia," Proc. Natl. Acad. Sci. U.S.A. 107, 6748–6752 (2010).

Cook, B.I. et al., 2016, "Spatiotemporal drought variability in the Mediterranean over the last 900 years," JGR Atmospheres, DOI: 10.1002/2015JD023929

Cullen, H.M., and P.B. deMenocal, 2000, North Atlantic Influence on TIgris-Euphrates Streamflow, International Journal of Climatology, 20: 853-863.

Cullen et al., 2000, "Climate change and the collapse of the Akkadian empire: Evidence from the deep sea," Geology 28, 379 (2000).

deMenocal, P.B., 2001, "Cultural responses to climate change during the late Holocene," Science 292, 667–673 (2001).

Gleick, P., 2014, Water, Drought, Climate Change, and Conflict in Syria, Weather, Climate, and Society, published online 1 July 2014, DOI:

Haug, G.H. et al., 2003, "Climate and the collapse of Maya civilization," Science 299, 1731–1735 (2003).

Hoerling, Martin, Jon Eischeid, Judith Perlwitz, Xiaowei Quan, Tao Zhang, Philip Pegion, 2012, On the Increased Frequency of Mediterranean Drought, J. Climate, 25, 2146–2161, doi:

Kaniewski, D. et al., 2012, Drought is a recurring challenge in the Middle East, PNAS 109:10, 3862–3867, doi: 10.1073/pnas.1116304109

Kaniewski, D. et al., 2013, "Environmental Roots of the Late Bronze Age Crisis," PLOS one, DOI: 10.1371/journal.pone.0071004

Kelley, C.P. et al., 2016, "Climate change in the Fertile Crescent and implications of the recent Syrian drought," PNAS vol. 112 no. 11, 3241–3246, doi: 10.1073/pnas.1421533112

Ortloff, C.R. and A.L. Kolata, 1992, "Climate and Collapse: Agro-Ecological Perspectives on the Decline of the Tiwanaku State," J. of Archaeological Science 1992, 195-221.

Wendel, JoAnna, 2015, Chinese Cave Inscriptions Tell Woeful Tale of Drought," EOS, 1 October 2015.

Yancheva, G. et al., 2007, "Influence of the intertropical convergence zone on the East Asian monsoon," Nature 445, 74–77 (2007).

The next post will be Wednesday.

Jeff Masters


Spring Outlook for U.S. Drought and Flood: Dry to the Southwest, Wet to the Southeast

By: Bob Henson , 4:48 PM GMT on March 18, 2016

An unexpectedly dry Southwest has put a twist on this spring’s prospects for drought evolution and flood risk, according to dual outlooks issued by NOAA on Thursday (see Figures 1 and 2). Mild weather has limited the winter snowpack over the Midwest, but saturated soils and near- to above-average streamflows will heighten the risk of moderate flooding this spring over the middle and lower Mississippi Valley, as well as the far Southeast and recently hard-hit east Texas and north Louisiana (Figure 1). Meanwhile, drought conditions are projected to improve near the intersection of California, Oregon, and Nevada, while holding steady over southern California and southwest Nevada and developing over most of Arizona and southwest New Mexico (Figure 2).

Figure 1. NOAA’s spring flood outlook for 2016, issued on Thursday, March 17. Image credit: NOAA/NWS.

Figure 2. NOAA’s outlook for drought risk through June, issued on Thursday, March 17, 2016. Image credit: NOAA/NWS/CPC.

The trickster El Niño of 2015-16
Normally during a strong El Niño, winters tend to be wetter than average from California across the southern Rockies to the Gulf Coast. One of the strongest El Niños on record has been in play this winter. Every El Niño has its quirks, but this one has gone against the grain in several ways, most notably in U.S. precipitation (Figures 3 and 4). Instead of slathering the southern tier of the U.S. with moisture (Figure 4), this El Niño has aimed its firehose in two distinct paths, as shown in Figure 3. One extends from central California north to Washington, and the other stretches from Texas and the Gulf Coast north and east into the Midwest and Southeast (plus south Florida). At times, these swaths have featured atmospheric rivers often referred to as the Pineapple Express (flowing from the central tropical Pacific to the West Coast) and the Maya Express (streaming from the Gulf of Mexico into the eastern U.S.).

Figure 3. Observed precipitation as a percentage of normal for the 90 days ending at 8:00 am EST Thursday, March 17, 2016. Image credit: NOAA/NWS/AHPS.

Figure 4 (at right). Enhancements in the risk of wet extremes (green) and dry extremes (red) when El Niño is present in the January-to-March period. These estimates are based on more than 120 years of U.S. climate data and the Multivariate ENSO Index, which has been extended back to 1871. Image credit: NOAA/ESRL/PSD.

A puzzling drought threatens to expand

Seasonal prediction is not for the faint of heart. Over much of the country, the rainfall patterns of the past three months (Figure 3) have been directly counter to what’s most likely during El Niño (Figure 4). The unexpectedly soggy Midwest and parched Southwest are especially striking. No major storms are in the immediate forecast for the Southwest, and Pacific storms become much less frequent from late March onward across southern California into Arizona and New Mexico.

At the NOAA/NWS Climate Prediction Center, climate scientist Michelle L’Heureux put together a comparison of anomalies (departures from average) in the 500-mb wind (about four miles above sea level) for the Dec-Jan-Feb period (see Figure 5, below). “What is pretty clear to me is that the Pacific jet is shifted north of its normal position,” L’Heureux told me. “The typical wintertime Aleutian low is weaker than it is normally during an El Nino event. The El Niño wave train is there; it is just not *exactly* where it is located typically. But as we’ve been saying for the past year, no single year perfectly matches the ‘typical’ pattern. These sort of shifts are not unexpected to us, which is why our forecasts are probabilistic.  A strong El Nino doesn't negate the fact there is uncertainty and it is intrinsic to the climate system.”

Figure 5. A comparison of 500-mb height and wind anomalies for the December-January-February period in a typical El Niño (left) and during 2015-16 (right). Blue colors indicate lower-than-average heights (corresponding to upper-level troughiness); red colors indicate above-average heights. Image credit: Courtesy Michelle L’Heureux, NOAA/NWS/CPC.

It sometimes rains in Southern California
I asked Alex Tardy, warning and coordination meteorologist with the National Weather Service in San Diego, to weigh in on how things look from where he sits. “We never told anyone there would be flooding or 100-year storms (though they told us that!),” said Tardy, “but with high confidence, we expected at least average precipitation, with the more likely scenario of 125% of average in our region. While most people expected flooding and torrential rains, we only had small doses of it in early January. In fact, we've had more impact in our region from squall lines and high wind (Jan. 5-6, Jan. 31, Mar. 7, and Mar. 11).”

Mountain snowpack in the Sierra Nevada is running near the seasonal average (Figure 6). By itself, that’s not enough to fully alleviate the impact of four-plus years of drought, but it should help keep the tap flowing at least modestly this year over southern California, which imports a good share of its water from the Sierra. Additional water comes into SoCal from the Colorado River basin, where the snowpack has been reasonably close to average, although powerhouse early storms over this region segued into a largely dry late winter. Meanwhile, the landscape of Southern California has received only a few moistening storms this winter. In its weekly U.S. Drought Monitor report issued Thursday, the National Drought Mitigation Center kept 35% of California in exceptional long-term drought (the most dire category). This area now extends roughly south and west of a line from San Francisco to Reno to Los Angeles.

Figure 6. The amount of water held in snowpack (snow water equivalent) across the western U.S. on Wednesday, March 16, 2016, as a percentage of the median value for the date. Much of the mountain West has near- or above-normal snow water equivalent, but values below 25% are widespread across New Mexico, Arizona, and southern Utah. Image credit: USDA/NRCS.

“Most of our region [far southern California] is going to end up with from 40% to 70% of normal precipitation for the water year, unless we get a couple of April or May anomalies,” Tardy told me. “Given the significant green-up that we saw from the winter rains we did receive, there definitely is a lot more small fuel available for wildfires.” Although San Diego and Los Angeles haven’t gotten the El Niño onslaught they expected, they may get more sultriness than usual again this summer, according to Tardy, as sea-surface temperatures remain unusually warm west of Baja California for the third straight year. Hot temperatures may add to the discomfort: San Diego just notched the warmest February in its 142-year climate record, only the latest in a series of heat records set over the last two years.

What the year 1992 tells us about today
The weird effects of this El Niño on U.S. precipitation don’t resemble the other two “super” events in recent times (1982-83 and 1997-98). However, there is something of an analog, according to Michael Ventrice (The Weather Company). Ventrice has analyzed the location and strength of the semi-permanent equatorial trough, or standing wave, in the Pacific that corresponds to each strong El Niño of recent decades. In a prototypical El Niño, the most unusually warm water and most concentrated convection (showers and thunderstorms) are in the far eastern tropical Pacific, which tends to bring the subtropical jet stream directly into the California coast. This winter, the most anomalous warm water and convection has been in the central Pacific, close to the Date Line. The associated subtropical jet has occasionally punched into the Southwest but more often headed toward northern California, Oregon, and Washington. This was also the case in April 1992, toward the tail end of the strong El Niño event of 1991-92. Then, as now, the focus of El Niño’s oceanic warming was near the Date Line. “The enhanced precipitation signal in April 1992 looked to have set up further north than what you'd expect in El Nino base states,” Ventrice told me. “The Northwest and northern California saw the bulk of enhanced rainfall. Southern California was fairly dry.”

Ventrice added: “We probably won’t see a repeat of April 1992 for the western U.S. pattern in April, as other external forcing mechanisms [including a recent strong split in the stratospheric polar vortex] are expected to overpower the El Nino base state and drive the pattern across the Northern Hemisphere during April. Long-range sub-seasonal models are indicating highly anomalous warmth and dry weather across the entire western U.S. during the first two weeks of April.”

A parting swipe from winter across the Northeast
A nor’easter developing off the East Coast late this weekend could bring a strip of moderate to heavy snow over or near the major coastal cities from Washington, D.C., to Boston, although much uncertainty remains. Total snowfall could end up as high as 3-6” in D.C. and 10” or more in Boston. There’s been plenty of conflict in the model guidance on the timing, strength, and positioning of this storm, which will make a big difference in snowfall potential. Given the lack of intensely cold air, a nighttime snowfall would be more likely to produce accumulations in the D.C. area, mostly on grassy surfaces. Capital Weather Gang will be tracking the storm closely. Steve Gregory examined the prospects of significant snow, and the longer-range U.S. outlook, in a post on Thursday.

Figure 7. Infrared image of Cyclone Emeraude at peak strength (Category 4, with 145 mph winds), collected by the VIIRS instrument aboard the NOAA/NASA Suomi NPP satellite. Image credit: NOAA.

Emeraude hits Category 4 strength in South Indian Ocean
Tropical Cyclone Emeraude has been putting on quite a show this week across the remote waters of the South Indian Ocean. Emeraude quickly spun up to Category 4 strength, rocketing from peak sustained winds of 65 mph at 06Z Wednesday to 145 mph at 06Z Thursday, according to the Joint Typhoon Warning Center. Emeraude underwent an eyewall replacement cycle later on Thursday, bringing down its intensity. Weak steering currents have allowed Emeraude to linger and pull up cooler water with reduced oceanic heat content, hastening its decline. At 06Z Friday (2:00 am EDT), Emeraude’s peak winds had dropped back to 100 mph. The cyclone could get a final shot at intensification late this weekend or early next week as it begins accelerating toward the southwest. Emeraude is not posing a threat to any land areas.

We’ll be back with our next post on Monday. Have a great weekend, everyone!

Bob Henson

El Niño Drought Flood

NOAA Agrees: February 2016 Was Earth's Warmest Month in Recorded History

By: Jeff Masters , 3:53 PM GMT on March 17, 2016

February 2016 was by far the planet's warmest February since record keeping began in 1880, and was also the warmest month relative to average of any month in the historical record, said NOAA's National Centers for Environmental Information (NCEI) on Thursday. As discussed here on Sunday, NASA also rated February 2016 as the warmest February as well as the warmest month in recorded history (measured as a departure from average.) In the NOAA database, February 2016 came in a full 0.32°C (0.58°F) warmer than the previous record-holder, February 2015--a truly astounding margin to break an all-time monthly global temperature record by (these records are typically broken by just a few hundredths of a degree.) The five warmest months since 1880 (as measured by departure from average in both the NOAA and NASA databases) were the past five months. The impressive global warmth in recent months is due to the steady build-up of heat-trapping greenhouse gases due to human activities, plus a spike due to a large amount of heat being released from waters in the Eastern Pacific due to the strong El Niño event there.

Figure 1. Departure from average for the global February temperature for the years 1880 - 2016. This year had by far the warmest February temperatures on record. Image credit: NOAA/National Centers for Environmental Information (NCEI).

February 2016 also marked the tenth consecutive month that the monthly temperature record has been broken and the fifteenth consecutive month (since December 2014) that the monthly global temperature ranked among the three warmest for its respective month in the NOAA database. Global ocean temperatures during February 2016 were the warmest on record, and global land temperatures were the second warmest on record. Global satellite-measured temperatures in February 2016 for the lowest 8 km of the atmosphere were the warmest in the 38-year record, according to the University of Alabama Huntsville (UAH). This is the fifth consecutive month the UAH database has registered a record monthly high.

Figure 2. Departure of temperature from average for February 2016, the warmest February for the globe since record keeping began in 1880. Record warmth was observed across portions of South America, much of southern Africa, southern and eastern Europe, around the Urals of Russia, most of Southeast Asia stretching to northern Australia, and portions of the Atlantic, Pacific, and Indian Oceans. Image credit: National Centers for Environmental Information (NCEI).

Strong El Niño quickly weakening
February 2016 still featured strong El Niño conditions in the equatorial Eastern Pacific, with sea surface temperatures (SSTs) 1.8°C above average on March 12 in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 1.5°C above average to be considered a strong El Niño. El Niño is weakening quickly--the event peaked in strength in late November 2015, when the weekly Niño3.4 temperature anomaly hit a record 3.1°C. NOAA expects a transition to neutral conditions during late Northern Hemisphere spring or early summer 2016, with a 50% chance of a transition to La Niña conditions during the fall.

Arctic sea ice falls to lowest February extent on record
Arctic sea ice extent during February 2016 was the lowest in the 38-year satellite record, according to the National Snow and Ice Data Center (NSIDC). This is the second consecutive month with a record-low sea ice extent.

Four billion-dollar weather disasters so far in 2016
According to the February 2016 Catastrophe Report from insurance broker Aon Benfield, four billion-dollar weather-related disasters have hit Earth so far in 2016:

1) Drought, Vietnam, 1/1 - 2/29, $6.7 billion, 0 killed
2) Winter Weather, Eastern U.S., 1/16 - 1/18, $2.0 billion, 58 killed
3) Winter Weather, East Asia, 1/20 - 1/25, $2.0 billion, 116 killed
4) Drought, Zimbabwe, 1/1 - 2/29, $1.6 billion, 0 killed

Notable global heat and cold marks set for February 2016
Hottest temperature in the Northern Hemisphere: 45.0°C (113.0°F) at Nguigmi, Niger, February 29: ties highest recorded temperature in February in the Northern Hemisphere
Coldest temperature in the Northern Hemisphere: -61.3°C (-78.3°F) at Summit, Greenland, February 11
Hottest temperature in the Southern Hemisphere: 47.8°C (118.0°F) at Mardie, Australia on February 12 and at Emu Creek, Australia on February 13
Coldest temperature in the Southern Hemisphere: -59.4°C (-74.9°F) at Dome Fuji, Antarctica, February 17
(Courtesy of Maximiliano Herrera.)

Major weather stations that set (not tied) new all-time heat or cold records in February 2016
El Bolson (Argentina) max. 37.5°C, 1 February
Niuafoou (Tonga) max. 35.5°C, 1 February: New National Record High for Tonga
Bauerfield Airport (Vanuatu) max. 35.7°C, 7 February: New National Record High for Vanuatu
Tanna White Grass Airport (Vanuatu) max. 35.2°C, 7 February
Saratata (Vanuatu) Max. 35.3°C, 7 February
Ouloup (New Caledonia, France) max. 35.3°C, 7 February
Ouanamham (New Caledonia, France) max. 34.6°C, 7 February
Lamap Malekula (Vanuatu) max. 36.2°C, 8 February: New National Record High for Vanuatu
Fuaamotu Airport (Tonga) max. 34.4°C, 8 February
Pekoa Airport Santo (Vanuatu) max. 35.0°C, 9 February
Ambon (Indonesia) max. 36.1°C, 10 February
Cilaos (Reunion Islands, France) max. 30.4°C, 11 February
Aneityum (Vanuatu) max. 34.3°C, 11 February
Hanan Airport (Niue, New Zealand) max. 33.9°C, 11 February
Udu Point (Fiji) max. 34.0°C, 14 February
Sola Vanua Lava (Vanuatu) max. 35.0°C, 16 February
Low Isles Lighthouse (Australia) max. 38.8°C, 16 February
Bello (Colombia) max. 36.4°C, 16 February
Bondoukou (Cote d' Ivoire) max. 40.6°C, 16 February
Mangalore City (India) max. 38.4°C, 18 February
Kozhikode (India) max. 37.6°C, 19 February
Kannur (India) max. 38.8°C, 19 February
Dimbokro (Cote d' Ivoire) max. 41.2°C, 20 February
Gagnoa (Cote d' Ivoire) max. 38.9°C, 21 February
Port Harcourt (Nigeria) max. 38.0°C, 21 February
Nabouwalu(Fiji) max. 35.2°C, 23 February
Suva Airport (Fiji) max. 34.9°C, 24 February
Piura (Peru) max. 38.4°C, 24 February
(Courtesy of Maximiliano Herrera.)

Four all-time national heat records and one all-time cold record set through mid-March 2016
So far in 2016, four nations or territories have tied or set all-time records for their hottest temperature in recorded history, and one (Hong Kong) has set an all-time cold temperature record. "All-time" record here refers to the warmest or coldest temperature ever reliably reported in a nation or territory. The period of record varies from country to country and station to station, but it is typically a few decades to a century or more. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. I use as my source for international weather records researcher Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Wunderground's weather historian Christopher C. Burt maintains a database of these national heat and cold records for 235 nations and territories on's extremes page. Here are 2016's all-time heat and cold records so far:

Botswana set its all-time hottest record on January 7, 2016, when the mercury hit 43.8°C (110.8°F) at Maun. The old record was set just the previous day  (January 6, 2016) with 43.5°C (110.3°F) at Tsabong. The record heat in Botswana during the first week of January was part of a remarkable heat wave that affected much of southern Africa, causing at least $250 million in drought-related damages to South Africa in the month. Mr. Herrera noted in an email to me that temperatures in South Africa at elevations between 1000 and 1600 meters were higher than any previous temperatures ever recorded at those altitudes anywhere in the world. The national heat records of Lesotho, Mozambique, Namibia, and Swaziland might all have fallen were it not for the lack of observing stations in the hottest areas. Lesotho has no weather stations anymore that issue the standard "synoptic" weather observations every six hours; Mozambique and Swaziland have closed all their stations in the hottest areas; and Namibia just closed its Noordower station, which was its hottest station.

Wallis and Futuna Territory (France) set a new territorial heat record with 35.8°C (96.4°F) on January 10, 2016 at Futuna Airport. This is the second year in a row that Wallis and Futuna has beaten its all-time heat mark; the previous record was a 35.5°C (95.9°F) reading on January 19, 2015 at the Futuna Airport.

Tonga set its all-time hottest record on February 1, 2016, when the mercury hit 35.5°C (95.9°F) at Niuafoou.

Vanuatu in the South Pacific set its all-time national heat record on February 8, 2016, when the mercury hit 36.2°C (97.2°F) at Lamap Malekula. The previous record was a 35.7°C (96.3°F) reading just the previous day (February 7, 2016) at the Bauerfield Efate Airport. All seven major weather reporting stations in Vanuatu beat or tied their all-time heat records February 7 - 8, 2016.

Hong Kong Territory (China) set its all-time coldest mark on January 24, 2016, when the mercury dipped to -5.7°C (21.7°F) at Tai Mo Shan.

We'll have a new post on Friday.

Jeff Masters

Climate Summaries

Did X Cause Y? A New Look at Attributing Weather Extremes to Climate Change

By: Bob Henson , 4:01 PM GMT on March 15, 2016

In a world filled with high-impact weather events, it’s only natural to wonder exactly why your town was beset with a heat wave, a destructive flood, or a deadly tornado. Today, such events occur in a different global atmosphere--one with more greenhouse gases than at any time in human history, thanks to human activity. A growing branch of atmospheric research is working to quantify the influence of human-induced climate change on various types of extreme weather, and there is real progress being made. “It is now possible to estimate the influence of climate change on some types of specific weather events,” said Rear Admiral David Titley (Pennsylvania State University) at a press briefing in Washington, D.C., last Friday. Titley chaired a U.S. National Academies committee that has just produced an important report, released on Friday. Attribution of Extreme Weather Events in the Context of Climate Change serves as a very useful guide to how this work is carried out, what it can and can’t do, and where the science is heading.

The idea behind attribution research is to provide reasonably satisfying answers to the query so often raised by policy makers and the public: did climate change have anything to do with this event? For years, scientists rightly pointed out that a changing climate doesn’t “cause” any particular event. Often, they added that it was impossible to know exactly what role climate change might have played in a particular weather happening, apart from basic conclusions about how the physics of a warming atmosphere should make certain events increasingly more or less likely.

Things are different now, as pointed out by Titley, the founding director of PSU’s Center for Solutions to Weather and Climate Risk. Attribution research, said Titley, “makes the future of climate real. It brings the future into the present.”

Figure 1. A schematic depiction of the National Academies assessment of the state of attribution science for different event types. The horizontal position of each event type reflects the level of understanding of the effect of climate change on that event type, and corresponds to the rightmost column in Figure 2. The vertical position of each event corresponds to scientific confidence in current capabilities for attributing specific events of that type to anthropogenic climate change; this vertical position draws on all three columns in Figure 2. In all cases, there is potential to increase event-attribution confidence by overcoming remaining challenges that limit the current level of understanding. Image credit: National Academies.

Figure 2. An overall assessment of the state of event attribution science for various event types. In each category, the committee has provided an estimate of confidence, based on the available scientific literature and the results of committee deliberation and judgment. Image credit: National Academies.

A spectrum of understanding
While this report has some fairly technical content, including heavy-duty statistical concepts, most of the terminology is well explained up front. This follows in the tradition of reports from the National Academies that speak to a broad, policy-interested audience on emerging science topics of keen public interest. It was high time for this particular report, said committee member Marshall Shepherd (University of Georgia), a WU contributing blogger and host of the Weather Channel’s popular “WX Geeks” series. In the headline of a Forbes commentary published on Friday, Shepherd heralds “The Death to One of the Most Abused Questions Ever: Was That Caused by Climate Change?” He cites this question as “so abused by ALL sides of the climate discussion.”

The ideas underlying the new report are summarized nicely in Figure 1, which places a variety of extreme weather events on a twofold spectrum: how well the influence of climate change is understood, and how confidently we can attribute specific instances of that event to climate change. Figure 2 elaborates on Figure 1 for each event category. As one might expect, our confidence in attribution goes up as our understanding increases--but not all events line up on this straight line. Tropical cyclones are a good example. There is a growing body of research concluding that we can expect the frequency of the most intense storms to rise in many parts of the world, a finding reiterated by the IPCC in 2013. Several studies in the last decade have suggested this trend is already under way, especially in the Atlantic. Yet tropical cyclones remain rare enough that it is tough to disentangle natural variability and observational uncertainty from the actual impact of climate change. Top global models are just now gaining the skill and resolution to simulate trends in Category 4 and 5 hurricanes over centuries, or to embed individual storms such as Hurricane Sandy into global-scale models that replicate the climate of the distant past and our greenhouse-warmed future.

Figure 3. Three potential ways in which a warming climate could affect heat and cold extremes: (top) shifting the entire distribution of observed temperatures toward a warmer average; (middle) increasing the variability of the distribution; and (bottom) skewing the curve in one direction or the other. Image credit: National Academies.

Heat waves and cold waves provide the best-understood and most-straightforward links: as climate change proceeds, we can expect more extreme heat and less extreme cold, with occasional exceptions here and there. In many areas, we have a century or more of good-quality temperature data, and this helps smooth the way toward making solid attributions. “Heat waves and cold waves may be the best candidates for assessing the reliability and robustness of attribution methods,” says the report.

Severe convective storms--intense thunderstorms and the hail, wind, and tornadoes they spawn--rank lowest on the spectrum in Figure 1. That’s not to imply that these storms are necessarily immune to the influence of greenhouse gases. The point is that (a) such influences are not yet crystal clear, in part because of sampling and observing issues, and (b) the huge natural variability in severe weather makes it hard to pluck out a climate-change signal for a particular storm. There is intriguing progress being made in these areas, though, some of which I’ll be covering in a future blog based on a meeting I attended last week at Columbia University (the 2nd Workshop on Severe Convection and Climate).

Figure 4. A man walks along the heavily damaged beach on November 2, 2012, in the Rockaway neighborhood of Queens, New York City, following the devastating arrival of Hurricane Sandy. Image credit: Spencer Platt/Getty Images.

Asking the right question
In order to study an attribution problem in a useful way, one needs to know exactly what the goal is. “Statements about attribution are sensitive to the way the questions are posed and the context within which they are posed,” the report notes. “For example, a scientific researcher might re-pose the question ‘was Hurricane Sandy caused by climate change?’ as ‘by how much did human influence on climate increase the odds of a tropical or post-tropical storm with winds greater than 65 knots making landfall in northern New Jersey?’”

Once a well-posed question is in hand, there’s a growing toolbox of techniques for researchers to draw on, amply discussed in the report. Many attribution studies include a mix of observations and model-based simulations, with the goal of determining how much more likely a certain type of event has become (such as a heat wave of a particular strength over the Midwest) due to the presence of human-produced greenhouse gases.

The most familiar source of attribution research for many of us is the dozens of studies compiled each year since 2012 in special issues of the Bulletin of the American Meteorological Society. These studies are useful in many ways, the report notes, but they shouldn’t be taken as a collective assessment of how climate change affects the whole gamut of extreme weather. For example, there is a selection bias at work. These reports focus on the highest-impact weather of a given year, so if a particular type of event has become increasingly rare (say, mammoth citrus-killing freezes in Florida), it’s much less likely to get examined.

Why the cookie crumbles
I helped take a very informal stab at an attribution spectrum in 2012 while part of the communications group at the University Corporation for Atmospheric Research. For this special project, we found ourselves touching on some of the questions of framing, phrasing, and methodology that are dissected much more thoroughly in this report. It’s encouraging to see how much the discipline has been growing, and how much vital knowledge it will be able to generate with the appropriate level of support and focus. The National Academies report should go a long way toward the “mainstreaming” of attribution research. It will also help journalists, educators, and others who need to put this often-esoteric science into terms that people can easily grasp. The links between greenhouse gases and extreme weather are far too important and intricate to be dismissed or broad-brushed.

Consider this tasty analogy provided by David Titley: we can think of a freshly-baked cookie as a weather event, with the ingredients being the factors that aligned to cause the event (i.e., large-scale atmospheric features), and the baking surface and the oven temperature representing conditions in which the event occurred (i.e., increasing greenhouse gases, decreasing sea ice). “When you bite into a cookie and it doesn’t taste right,” said Titley, “it can be hard to determine what went wrong.”

You can download a PDF of the full report at the National Academies website. Jeff Masters will be back on Thursday with coverage of NOAA’s highly anticipated report on global climate for February. See our report from this past weekend on NASA’s blockbuster data.

Bob Henson

Climate Change

February Smashes Earth's All-Time Global Heat Record by a Jaw-Dropping Margin

By: Jeff Masters and Bob Henson , 7:46 PM GMT on March 13, 2016

On Saturday, NASA dropped a bombshell of a climate report. February 2016 has soared past all rivals as the warmest seasonally adjusted month in more than a century of global recordkeeping. NASA’s analysis showed that February ran 1.35°C (2.43°F) above the 1951-1980 global average for the month, as can be seen in the list of monthly anomalies going back to 1880. The previous record was set just last month, as January 2016 came in 1.14°C above the 1951-1980 average for the month. In other words, February has dispensed with this one-month-old record by a full 0.21°C (0.38°F)--an extraordinary margin to beat a monthly world temperature record by. Perhaps even more remarkable is that February 2016 crushed the previous February record--set in 1998 during the peak atmospheric influence of the 1997-98 “super” El Niño that’s comparable in strength to the current one--by a massive 0.47°C (0.85°F).

Figure 1. Monthly global surface temperatures (land and ocean) from NASA for the period 1880 to February 2016, expressed in departures from the 1951-1980 average. The red line shows the 12-month running average. Image credit: Stephan Okhuijsen,, used with permission.

An ominous milestone in our march toward an ever-warmer planet
Because there is so much land in the Northern Hemisphere, and since land temperatures rise and fall more sharply with the seasons than ocean temperatures, global readings tend to average about 4°C cooler in January and February than they do in July or August. Thus, February is not atop the pack in terms of absolute warmest global temperature: that record was set in July 2015. The real significance of the February record is in its departure from the seasonal norms that people, plants, animals, and the Earth system are accustomed to dealing with at a given time of year. Drawing from NASA’s graph of long-term temperature trends, if we add 0.2°C as a conservative estimate of the amount of human-produced warming that occurred between the late 1800s and 1951-1980, then the February result winds up at 1.55°C above average. If we use 0.4°C as a higher-end estimate, then February sits at 1.75°C above average. Either way, this result is a true shocker, and yet another reminder of the incessant long-term rise in global temperature resulting from human-produced greenhouse gases. Averaged on a yearly basis, global temperatures are now around 1.0°C beyond where they stood in the late 19th century, when industrialization was ramping up. Michael Mann (Pennsylvania State University) notes that the human-induced warming is even greater if you reach back to the very start of the Industrial Revolution. Making matters worse, even if we could somehow manage to slash emissions enough to stabilize concentrations of carbon dioxide at their current level, we are still committed to at least 0.5°C of additional atmospheric warming as heat stored in the ocean makes its way into the air, as recently emphasized by Jerry Meehl (National Center for Atmospheric Research). In short, we are now hurtling at a frightening pace toward the globally agreed maximum of 2.0°C warming over pre-industrial levels.

El Niño and La Niña are responsible for many of the one-year up-and-down spikes we see in global temperature. By spreading warm surface water across a large swath of the tropical Pacific, El Niño allows the global oceans to transfer heat more readily into the atmosphere. El Niño effects on global temperature typically peak several months after the highest temperatures occur in the Niño3.4 region of the eastern tropical Pacific. The weekly Niño3.4 anomalies peaked in mid-November 2015 at a record +3.1°C , so it’s possible that February 2016 will stand as the apex of the influence of the 2015-16 El Niño on global temperature, although the first half of March appears to be giving February a run for its money. We can expect the next several months to remain well above the long-term average, and it remains very possible (though not yet certain) that 2016 will top 2015 as the warmest year in global record-keeping.

Lower atmosphere also sets a record in February
Satellite-based estimates of temperature in the lowest few miles of the atmosphere also set an impressive global record in February. Calculations from the University of Alabama in Huntsville show that February’s reading in the lower atmosphere marked the largest monthly anomaly since the UAH dataset began in late 1978. UAH's Dr. Roy Spencer, who considers himself a climate change skeptic, told Capital Weather Gang earlier this month, “There has been warming. The question is how much warming there’s been and how does that compare to what’s expected and what’s predicted.” The satellite readings apply to temperatures miles above Earth’s surface, rather than what is experienced at the ground, and a variety of adjustments and bias corrections in recent years (including an important one just this month) have brought satellite-based readings closer to the surface-observed trends.

Figure 2. Anomalies (departures from average) in surface temperature across the globe for February 2016, in degrees Centigrade, as analyzed by NASA’s Goddard Institute for Space Studies. Image credit: NASA/GISS.

Arctic leads the way
Figure 2 shows a big factor in the February result: a superheated Arctic. As shown by the darkest-red splotches in the figure, large parts of Alaska, Canada, eastern Europe, and Russia, as well as much of the Arctic Ocean, ran more than 4.0°C (7.2°F) above average for the month. This unusual warmth helped drive Arctic sea ice to its lowest February extent on record in February 2016. The tremendous Arctic warmth was probably related to interactions among warm air streaming into the Arctic, warm water extending poleward from the far northeast Atlantic, and the record-low extent of Arctic sea ice. Ground Zero for this pattern was the Barents and Kara Seas, north of Scandinavia and western Russia, where sea ice extent was far below average in February. Typically, the Norwegian archipelago of Svalbard--which includes the northernmost civilian settlements on Earth--is largely surrounded by ice from early winter into spring. This winter, the edge of the persistent ice has stayed mostly to the north of Svalbard, which has helped an absurd level of mildness to persist over the islands for months. Air temperatures at the Longyearbyen airport (latitude 78°N) have been close to 10°C (18°F) above average over the past three-plus months. This is the single most astounding season-long anomaly we’ve seen for any station anywhere on Earth. (If anyone can beat it, please let us know and we’ll add it here!) Update (March 14): It turns out in the winter of 2013-14, Svalbard was even more amazingly mild: the Dec-Jan-Feb average was -4.73°C, compared to the -5.12°C average from this past winter. According to Deke Arndt (NOAA/NCEI), a handful of high-latitude stations in Alaska, Canada, Kazakhstan, Norway, and Russia have racked up full-winter anomalies during past years in the range of 6°C to 8°C above the 1981-2010 average. At least some of these might be large enough to beat out the 2013-14 and 2015-16 Svalbard anomalies of around 10°C if these other readings were recalculated against the generally cooler 1961-1990 base period used by the Norwegian Meteorological Institute.

Figure 3. Daily temperatures (in Celsius, °C) for the past year at the Longyearbyen Airport, Svalbard, Norway, located at latitude 78°N. The black line shows the seasonal average; blue and red traces show the day-to-day readings. The darker blue and red line shows the 30-day running average, which was 10.2°C (18.4°F) above normal in February. Thus far in March, the anomaly (not shown here) has been even larger, close to 12°C (22°F). Image credit: Norwegian Meteorological Institute.

February's heat had severe impacts
It has long been agreed upon in international climate negotiations that a 2°C warming of the Earth above modern pre-industrial levels represents a "dangerous" level of warming that the nations of the world should work diligently to avoid. The December 2015 Paris Climate Accord, signed by 195 nations, included language on this, and the Accord recommend that we should keep our planet from warming more than 1.5°C, if possible. Although the science of attributing extreme weather events to a warming climate is still evolving (more on this in an upcoming post), February 2016 gave us a number of extreme weather events that were made more probable by a warmer climate, giving us an excellent example of how a 2°C warming of the climate can potentially lead to dangerous impacts. And, as we have been repeatedly warned might likely be the case, these impacts came primarily in less developed nations--the ones with the least resources available to deal with dangerous climate change. According to the February 2016 Catastrophe Report from insurance broker Aon Benfield, three nations suffered extreme weather disasters in February 2016 that cost at least 4% of their GDP--roughly the equivalent of what in the U.S. would be five simultaneous Hurricane Katrinas. According to EM-DAT, the International Disaster Database, these disasters set records for the all-time most expensive weather-related disaster in their nations' history. For comparison, nine nations had their most expensive weather-related natural disasters in history in all of 2015, and only one did so in 2014. Here are the nations that have set records in February 2016 for their most expensive weather-related natural disaster in history:

Vietnam has suffered $6.7 billion in damage from its 2016 drought, which has hit farmers especially hard in the crucial southern Mekong Delta. This cost is approximately 4% of Vietnam's GDP, and beats the $785 million cost (2009 USD) of Typhoon Ketsana of September 28, 2009 for most expensive disaster in their history. In this image, we see a boy holding his brother walking across a drought-hit rice field in Long Phu district, southern delta province of Soc Trang on March 2, 2016. Image credit: STR/AFP/Getty Images.

Zimbabwe has suffered $1.6 billion in damage from its 2016 drought. This is approximately 12% of their GDP, and beats the $200 million cost (2003 USD) of a February 2003 flood for most expensive disaster in their history. Zimbabwe's President Robert Mugabe on February 5, 2016 declared a 'state of disaster' in many rural areas hit by a severe drought, with more than a quarter of the population facing food shortages. This photo taken on February 7, 2016 shows the fast-drying catchment area of the Umzingwani dam in Matabeleland, Southwestern Zimbabwe. Image credit: Ziniyange Auntony/AFP/Getty Images.

Fiji suffered $470 million in damage from Category 5 Cyclone Winston's impact in February. This is approximately 10% of their GDP. The previous costliest disaster in Fiji was Tropical Cyclone Kina in January 1993, at $182 million (2016 USD) in damage. In this image, we see how Category 5 winds can completely flatten human-built structures: Fiji's Koro Island received a direct hit from Winston when the storm was at peak strength with 185 mph winds. Image credit: My Fijian Images and Jah Ray.

One other severe impact from February's record heat is the on-going global coral bleaching episode, just the third such event in recorded history (1998 and 2010 were the others.) NOAA's Coral Reef Watch has placed portions of Australia's Great Barrier Reef under their "Alert Level 1", meaning that widespread coral bleaching capable of causing coral death is likely to occur. Widespread but minor bleaching has already been reported on the reef, and the coming month will be critical for determining whether or not the reef will experience its third major mass bleaching event on record.

Figure 4. Annual mean carbon dioxide growth rates for Mauna Loa, Hawaii. In the graph, decadal averages of the growth rate are also plotted, as horizontal lines for 1960 through 1969, 1970 through 1979, and so on. The highest one-year growth in CO2 was in 2015, at 3.05 ppm. The El Niño year of 1998 was a close second. The estimated uncertainty in the Mauna Loa annual mean growth rate is 0.11 ppm/yr. Image credit: NOAA’s Greenhouse Gas Reference Network.

Last year saw Earth’s highest-ever increase in carbon dioxide
Despite efforts to slow down human emissions of carbon dioxide, 2015 saw the biggest yearly jump in global CO2 levels ever measured, said NOAA last week. The concentration of atmospheric carbon dioxide measured at NOAA’s Mauna Loa Observatory in Hawaii jumped by 3.05 parts per million during 2015, the largest year-to-year increase since measurements began there in 1958. In another first, 2015 was the fourth consecutive year that CO2 concentrations grew more than 2 ppm, said Pieter Tans, lead scientist of NOAA's Global Greenhouse Gas Reference Network. “Carbon dioxide levels are increasing faster than they have in hundreds of thousands of years,” Tans said. “It’s explosive compared to natural processes.” The last time the Earth experienced such a sustained CO2 increase was between 17,000 and 11,000 years ago, when CO2 levels increased by 80 ppm. Today’s rate of increase is 200 times faster, said Tans. In February 2016, the average global atmospheric CO2 level stood at 402.59 ppm. Prior to 1800, atmospheric CO2 averaged about 280 ppm.

The big jump in CO2 in 2015 is partially due to the current El Niño weather pattern, as forests, plant life and other terrestrial systems responded to changes in weather, precipitation and drought. In particular, El Niño-driven drought and massive wildfires in Indonesia were a huge source of CO2 to the atmosphere in 2015. The largest previous global increase in CO2 levels occurred in 1998, which was also a strong El Niño year. However, continued high emissions from human-caused burning of fossil fuels are driving the underlying growth rate. We are now approaching the annual peak in global CO2 levels that occurs during northern spring, after which the value will dip by several ppm. It is quite possible that the annual minimum in late 2016 will for the first time fail to get below 400 ppm, as predicted by Ralph Keeling (Scripps Institution of Oceanography) last October. To track CO2 concentrations at Mauna Loa and global CO2 concentrations, visit NOAA’s Greenhouse Gas Reference Network and the Keeling Curve website (Scripps).

For more on Saturday’s bombshell report, check out the coverage from Andrew Freedman (Mashable), Eric Holthaus (Slate), and Tom Yulsman (Scientific American/ImaGeo). We’ll have a follow-up post later this week on NOAA’s global climate report for February and for the Dec-Feb period, along with a roundup of all-time records set in February at major stations around the world. Our next post will be up by Tuesday at the latest.

Jeff Masters and Bob Henson

Climate Summaries Climate Change

Floods From up to 20 Inches of Rain Create State of Emergency in Louisiana

By: Jeff Masters , 4:22 PM GMT on March 11, 2016

A state of emergency has been declared by Governor John Bel Edwards for the entire state of Louisiana after a four-day deluge of rain dumped up to 20" of rain over northern portions of the state. The resulting record flooding has forced a call-up of the National Guard to help evacuate thousands of people from their homes. Five storm-related deaths have been reported since Monday--three in Louisiana and one each in Oklahoma and Texas. Hundreds of roads have been closed, including portions of two major interstate highways. One bridge collapsed on Louisiana Highway 557 in Ouchita Parish.

Figure 1. A bridge collapsed on Louisiana Highway 557 in Ouchita Parish, Louisiana, on March 10, 2016. Image credit: Louisiana DOTD.

Figure 2. Satellite-derived Integrated Water Vapor (the total amount of rain, in centimeters, that would result from condensing all water vapor in a column of air) as of 7 am EST March 11, 2016. Two "atmospheric rivers" of water vapor are seen affecting the U.S.--one from the Eastern Pacific and Western Caribbean flowing across Mexico into the Southern U.S., and one extending from the tropics south of Hawaii to the coast of California. Image credit: NOAA/ESRL.

Figure 3. Observed 72-hour precipitation for the period ending at 10 am EST Friday, March 11, 2016. Portions of northern Louisiana received over 20" of rain, and a large area of 8+" fell over portions of Eastern Texas, Northern Louisiana, Southeast Arkansas and Northwest Mississippi. Image credit: NOAA/NWS.

An upper-level low tapping an atmospheric river of moisture was responsible
The upper low over Mexico responsible for the deluge was able to tap into an atmospheric river of moisture from both the Western Caribbean and the Eastern Pacific, and was still bringing record amounts of water vapor to the Gulf Coast on Friday morning. The 7 am EST Friday March 11, 2016 upper-air balloon sounding from Jackson, MS set a new record for most precipitable water on record for any day during the December - March period: 1.97". New Orleans, LA set a record on Friday morning for most precipitable water of any astronomical winter date: 2.14". The record atmospheric moisture this week has led to rainfall amounts one would expect to occur only once every 200 years (a 0.5% chance of occurrence in a given year) over portions of northern Louisiana. According to the latest NOAA Storm Summary, as of 9 am EST Friday, a rain gauge two miles from the city of Monroe, Louisiana had received 20.90" of rain since Monday, and Shreveport, Louisiana had picked up 19.00" at Barksdale Air Force Base. Over a foot of rain was recorded at several locations in Southern Arkansas.

Figure 4. Total Precipitable Water over Jackson, Mississippi from 1948 - 2016, with the record amount from 7 am EST Friday March 11, 2016 shown. Image credit: NOAA/SPC.

Figure 5. The Sabine River near Burkeville, Louisiana reached its highest water level on record Friday morning, beating the previous record set in February 1999 by over five feet. Water levels for this gauge go back to 1884. Image credit: NOAA.

Figure 6. VIIRS satellite imagery from Thursday afternoon, March 10, 2016, shows the record-strength upper-level low centered over central Mexico that brought torrential rains and record flooding to Louisiana. Image credit: NASA.

Record warmth continues across the Northeast
As if Wednesday’s high of 77°F left any doubt that spring had sprung early in New York City, Thursday doubled up with a high of 79°F.  This broke the previous day’s record as the warmest temperature ever notched so early in the year in 145 years of record-keeping at Central Park. Even more impressive was Thursday’s “low” temperature: a ridiculous 63°F! That’s the warmest daily minimum Central Park has seen during any winter--or for that matter, on any date falling between November 10 and March 28--since measurements began in 1871. For maximum shock value, we can employ Thursday’s average temperature of 71°F [calculated by adding the daily high and low and dividing by 2]. A reading like this would be most likely to occur in New York during late June or late August. The latest such reading in Central Park annals is 71°F on November 2, 1971; the record-earliest value this warm was 71.5°F on March 28, 1998. Many other record highs were again set across the Northeast on Thursday, just a day after dozens of cities set records for the hottest temperatures on record for so early in the year. A weak front will push temperatures back near normal this weekend, but only briefly, before another spell of warmth kicks in next week across most of the central and eastern U.S.

The forecast: more flooding in the South
Thankfully, the stalled-out record-strength upper-level low pressure system responsible for the historic flooding is finally on the move, headed northwards across Texas. The low will still be tapping into the atmospheric river of moisture responsible for this week's heavy rains, and will bring additional widespread heavy rains of 2 - 5" over the Central Gulf Coast states through Saturday, with a few areas up to 10" possible. By Sunday, the heavy rains should end as the upper-level low weakens and the flow of moisture from the Gulf gets cut off.

Figure 7. Predicted precipitation for the 2-day period ending 7 am EST Sunday, March 13, 2016. Heavy rains in excess of 5" are expected over coastal Mississippi and Southeast Louisiana, including New Orleans. Image credit: National Weather Service.

Heavy rains and high winds hit U.S. West Coast
Meanwhile, another storm system with its own atmospheric river of moisture has been hitting the U.S. West Coast, bringing flooding rains and heavy mountain snows to California. Wind gusts in excess of 50 mph swept across much of Washington State on Thursday, causing some impressive damage and knocking out power to 100,000 customers. According to the NWS in Seattle, the top wind gust was 109 mph on top of Mt. Baker.

Wunderblogger Lee Grenci has a post on how the upper-level low over Mexico was not truly a "cut-off" low like we called it in previous posts, but rather a "closed low."

Jeff Masters and Bob Henson


Record-Strength Upper Low Brings Extreme Rains to South U.S., Thundersnow to Mexico

By: Bob Henson and Jeff Masters , 4:51 PM GMT on March 10, 2016

A remarkably rare atmospheric event is unfolding over Mexico and the Southern U.S., where an upper-level low pressure system of unprecedented strength in the historical record for that location has stalled out, bringing multiple days of torrential rain to the Southern U.S. and snow to the mountains of Mexico. The upper low tapped into an atmospheric river of moisture from both the Western Caribbean and the Eastern Pacific, bringing rainfall amounts one would expect to occur only once every 200 years (a 0.5% chance of occurrence in a given year) over portions of northern Louisiana. According to the latest NOAA Storm Summary, as of 9 am EST Thursday, the city of Monroe, Louisiana had received 17.25" of rain since Monday, and Shreveport had picked up 16.70" at Barksdale Air Force Base. The heavy rains led to numerous high water rescues, evacuation of at least 3,500 homes, and closures of hundreds of roads. Portions of two interstate highways in northern Louisiana--I-20 and I-49--were closed on Thursday morning due to flooding, according to Three drownings have been reported since Monday from the storm system--one each in Texas, Oklahoma and Louisiana.

Figure 1. Flood damage in Haughton, Louisiana, on March 9, 2016. Thirty homes near Haughton were inundated by flood waters on Tuesday night, forcing evacuations. Image credit: Michael Dean Newman.

Figure 2. A webcam from Zacatecas, Mexico, catches snow falling on Wednesday, March 9, 2016. Thundersnow was reported at the city’s official reporting site. Image credit:, courtesy Eric Blake.

Figure 3. Observed 48-hour precipitation for the period ending at 10 am EST Thursday, March 10, 2016. Portions of northern Louisiana received over 16" of rain, and a large area of 8+" fell over portions of Eastern Texas, Northern Louisiana, Southeast Arkansas and Northwest Mississippi. Image credit: NOAA/NWS.

Figure 4. Average recurrence interval in years for the 24-hour rainfall amounts that fell ending at 7 am EST Wednesday, March 9, 2016. Rainfall amounts one would expect to occur only once every 200 years (a 0.5% chance of occurrence in a given year) fell over some portions of northern Louisiana just east of Shreveport. MetStat computed the recurrence interval statistics based on gauge-adjusted radar precipitation and frequency estimates from NOAA Atlas 14 Volume 8, published in 2013 ( The real-time analysis (observed) can be monitored for free at: or on their Facebook page.  MetStat also offers a subscription for precipitation interval forecasts and analyses at

Figure 5. The Bayou Dorcheat at Lake Bistineau, Louisiana reached its highest water level on record Thursday morning. The extreme rains in northern Louisiana have poured into local lakes and rivers, sending a few close to or in excess of their highest water levels on record. On Friday, the Sabine River near Burkeville is predicted to exceed its highest crest since 1884. Image credit: NOAA.

Weather weirding par excellence: Strongest upper low ever observed over central Mexico?
This upper low originated from energy that moved across southern California late in the weekend, producing heavy thunderstorms. Rather than barreling across the southeast U.S., the powerful subtropical jet stream carved out a progressively deeper trough into Mexico that cut off from the jet stream, forming a slow-moving closed low. At 00Z (7:00 pm EST) Thursday, this cold-cored upper low was centered in central Mexico, roughly in the vicinity of Guadalajara. Thundersnow was reported on Wednesday in Mexico at Zacatecas (altitude 8010 feet), about 200 miles north of Guadalajara. However, weather records researcher Maximiliano Herrera told us in an email that snow in the mountains of northern Mexico has occurred in April, May and even early June, so is not that unusual. As shown in Figure 7 below, this upper low featured a large 558-decameter contour (the 558 dm, which is 5580 meters, refers to the height at which the atmospheric pressure is 500 mb, or about half of the typical surface pressure). Such a large, strong upper low appears to be an unprecedented event in modern weather observations for Mexico; upper-air analyses dating back to 1948 from the NCEP/NCAR reanalysis project suggest that no previous upper low in this region has been strong enough to generate a 558-dm contour. During the last “super” El Niño, in mid-December 1997, a powerful upper trough extended south from the United States, producing what was reportedly the first snow observed at Guadalajara since February 1881. Low-level temperatures have not been quite as cold this time around, given that it’s now early March rather than mid-December, but the thundersnow reported at Zacatecas indicates the strong instability being produced by the deep cold at upper levels. The gradient between this upper low and a strong upper ridge over the eastern U.S. has also intensified the southerly flow pumping moisture into the south-central states.

Figure 6. GOES satellite imagery from 0245Z Thursday, March 10, 2016 (9:30 pm EST Wednesday), shows the immense swirl of an upper-level low centered over central Mexico, as well as the stream of moisture extending from the waters of the eastern tropical Pacific (still warmed by El Niño) across the western Gulf of Mexico into Texas and Louisiana. Image credit: NASA Earth Science Office and NOAA.

Figure 7. 500-mb map for 00Z (7:00 pm EST) Thursday, March 10, 2016, as initialized in the GFS model. Image credit: NOAA/NCEP.

Figure 8. 500-mb map for 12Z (7:00 am EST) Friday, December 12, 1997, about the time that the upper trough had reached its maximum extent into Mexico. Image credit: NOAA Daily Weather Map.

Premature spring warmth swaddles Northeast
Dozens of temperature records melted like so much gelato beneath sun-filled skies across much of the Northeast on Wednesday. Boston basked in temperatures that topped out at 77°F--not just a daily record, but the city’s warmest official reading on any day in astronomical winter since records began there in 1872. New York City’s Central Park also had its earliest 77°F in records that, likewise, go back to 1872. The uncannily mild air served as a fitting curtain call after New England’s warmest meteorological winter on record (Dec-Feb). The lack of persistent snow cover across New York and New England helped give this week’s warmth an extra boost. Some of the records set on Wednesday, March 9, 2016 included:

Earliest 80°F on record
Albany, NY:  81°F (previous record March 16, 1990)
Hartford, CT: 81°F (previous record March 20, 1945)
Newark, NJ: 82°F (previous record March 13, 1990)Poughkeepsie, NY: 82°F (previous record March 13, 1990)

Earliest 75°F on record
Boston, MA: 77°F (previous record March 14, 1946)
Concord, NH: 77°F (previous record March 18, 2012)

Earliest 70°F on record
Glens Falls, NY 77°F (previous record March 13, 1990)

Earliest 65°F on record
Montpelier, VT: 66°F (previous record March 15, 1990)
St. Johnsbury, VT: 65°F (previous record March 16, 1990)

Figure 9. Spring fever sweeps across the campus of Columbia University in New York City on Wednesday, March 9. Image credit: Bob Henson.

The forecast: more flooding in the South, more warmth for the East
Looking ahead, the atmospheric river of moisture responsible for this week's heavy rains has shifted slightly eastwards, and was still at near-record levels in excess of 200% of normal on Thursday morning. The 12Z Thursday morning balloon sounding at Lake Charles, Louisiana showed an astonishing 2.15" of precipitable water in the atmosphere--the second highest value on record for the months of December - April (thanks go to Peter Mullinax, ‏@wxmvpete, for this stat.) This moisture will continue to feed torrential rains over Louisiana, Arkansas and Mississippi on Thursday and Friday.

Figure 10. Predicted precipitation for the 3-day period ending 7 am EST Sunday, March 13, 2016. Heavy rains in excess of 7" (brown colors) are expected over eastern Louisiana, including New Orleans. Image credit: National Weather Service.

A solid week of unusually mild air lies in store for most of the nation east of the Rockies. Though we can expect dozens if not hundreds of daily record highs to be set between now and then, it looks highly unlikely this mild spell will dislodge the Great Warm Wave of March 2012 from its place of pride in our late-winter/early-spring climate annals. That phenomenal stretch of warmth brought close to a week of temperatures topping 80°F from the Midwest to the Northeast. The town of Lapeer, Michigan, hit 90°F on March 21 (setting a state record for March). Readings that would have broken records for April, much less March, extended into the Canadian Maritimes.

Video 1. Drone footage of flooding in Bossier City in Northern Louisiana on March 9, 2016. Thanks go to wunderground member Skyepony for posting this video in the blog comments.

Bob Henson and Jeff Masters


Flash Flood Emergency in Northern Lousiana: Over a Foot of Rain in 24 Hours

By: Jeff Masters , 4:26 PM GMT on March 09, 2016

A Flash Flood Emergency has been declared in Northwest Louisiana, including the city of Shreveport, where over a foot of rain fell in just 24 hours, from Tuesday morning through Wednesday morning. At Shreveports's Barksdale Air Force Base, 13.16" had fallen as of 10 am EST Wednesday, and over 14 inches of rain fell just to the southeast of Shreveport near Bossier City. The heavy rains have led to numerous high water rescues and flooded homes and streets. Near Shreveport, up to 80 homes were flooded and a nursing home had to be evacuated due to rising waters, according to the Associated Press, and evacuations have been ordered in Greenwood, Haughton, Homer, Minden and Rayville, Louisiana. The flooding problems extend into Eastern Texas, where multiple bridges have been washed out northeast of Marlin, Texas. Although the heaviest rains moved out of Eastern Texas and Northern Louisiana late Wednesday morning, near-record levels of atmospheric moisture for this time of year--more than 200% of average--remain in place over the region, and renewed rounds of heavy rain are likely through Friday. Extreme flooding rains were spreading into Southern Arkansas on Wednesday morning, and rainfall amounts of a foot in 24 hours are possible there, as well. Additional major flash flooding over the next few days is also possible in Houston, San Antonio, Austin, Shreveport, Little Rock, Memphis and New Orleans.

Figure 1. Flooding in Bossier Parish, Louisiana on March 9, 2016 submerged some houses up to their roofs. Numerous water rescues were made Tuesday night as high water started to pile up in parts of Louisiana after heavy rainfall. (CBS News Correspondent @DavidBegnaud) 

Although flooding is the major concern from this slow-moving storm system, severe thunderstorms and a few tornadoes are also expected through Thursday in some of the same parts of the Lower Mississippi Valley and Gulf Coast. So, far, the storm had spun up three tornadoes since Monday. An EF1 tornado caused damage near Cool, Texas Monday evening, and an EF1 tornado touched down near Tolar, Texas, southwest of Ft. Worth Tuesday morning. An EF1 tornado also left a narrow path of damage in Stephenville, Texas early Tuesday. Severe thunderstorms hit the Ft. Worth, Texas region, with a 66 mph gust at the Ft. Worth Meacham Airport. Baseball size hail pounded Voca, Texas Tuesday evening, while hail to the size of golf balls covered the ground in both Evant and Jonesboro, Texas. Two drowning deaths have been attributed to the storm system: a man in Broken Bow, OK that drove across a flooded bridge and got swept away, and a man in a canoe on Dickinson Bayou near Hwy 3 in Dickinson, TX where the wind blew him into the water. Thanks go to wunderground members RitaEvac and Skyepony for this info.

Figure 2. Storm damage from early Tuesday in Frisco, Texas. (@NTXStrmTrackers/ 

A "cut-off" low is responsible
A large low pressure system (a "cut-off" low) has separated from the jet stream, and will stay parked over the U.S./Mexico border region during the next few days. The counter-clockwise flow of air around this low is bringing up plenty of warm, moisture-laden air from the tropics along the east side of the low, causing the heavy rains we've observed. By this weekend, when all of this rain has had time to flow into area rivers, expect to see several rivers crest at near-record flood levels. Sea Surface Temperatures (SSTs) are near average over the Gulf of Mexico, which will keep the amount of moisture available to this week's storms lower than would be the case if SSTs were unusually warm. However, the cut-off low has tapped into a moisture source in the deep tropics over the Eastern Pacific where SSTs are record warm. An "atmospheric river" of water vapor can be seen on satellite images extending from the record-warm El Niño-heated waters south of Mexico directly into the Southern U.S. This warm, moist air is very unstable, which will help contribute to severe thunderstorms with a few tornadoes over the Southern U.S. today through Friday.

Figure 3. Observed 24-hour precipitation for the period ending at 9 am EST Wednesday, March 9, 2016. Portions of northern Louisiana received over a foot of rain, and a large area of 8+" fell over portions of Eastern Texas and Northern Louisiana. Image credit: NOAA/NWS.

Figure 4. Lots more rain on the way: predicted precipitation for the 3-day period ending 7 am EST Saturday, March 12, 2016. Image credit: National Weather Service.

Jeff Masters


U.S. Has its Warmest Winter on Record; Major Deluge Coming to TX, AR, LA

By: Jeff Masters , 5:31 PM GMT on March 08, 2016

The contiguous U.S. just experienced its warmest winter on record, said NOAA's National Centers for Environmental Information on Tuesday, with the three-month meteorological winter period of December 2015 through February 2016 coming in tops for the 121-year period of record that began in 1895. Every state had above-average temperatures, and 36 states had a top-ten warmest winter on record. The most notable warmth was in the Northeast, where all of New England had their warmest winter on record. The record-warm U.S. winter was made possible by very warm conditions in December and February: December 2015 was the warmest December on record for the contiguous U.S., and February 2016 was the 6th warmest February. January 2016 was a bit cooler, ranking as the 33rd warmest January. NOAA will release its winter temperature rankings for the entire globe on March 17. I expect that we will see Earth set a new record for warmest winter on record globally, since December 2015 and January 2016 were the two warmest months in recorded history (expressed as a departure from average.) The record warmth is due to the steady accumulation of heat-trapping gases in Earth's atmosphere due to human activities, plus an extra approximately 10% bump in temperatures due to the slowly waning record-strength El Niño event in the Eastern Pacific.

Figure 1. State-by-state temperature rankings for the winter period December 2015 through February 2016. Every state had above-average temperatures, and 36 states had a top-ten warmest winter on record. The most notable warmth was in the Northeast, where all of New England had their warmest winter in the 121-year period of record. Image credit: NOAA/NCEI.

Figure 2. State-by-state precipitation rankings for the winter period December 2015 through February 2016. Only two states had below-average precipitation, and ten states had a top-ten wettest winter on record. One state--Iowa--had their wettest winter on record. Image credit: NOAA/NCEI.

Major deluge headed for Arkansas, Louisiana, and East Texas
A large low pressure system (a "cut-off" low) has separated from the jet stream, and will stay parked over the U.S./Mexico border region during much of the week. The counter-clockwise flow of air around this low will bring up plenty of warm, moisture-laden air from the tropics along the east side of the low, resulting in an extended period of very heavy rains over Arkansas, Louisiana, and East Texas this week. With rainfall amounts in excess of 7" expected over this region, flash flooding will be the main concern this week. By this weekend, when all of this rain has had time to flow into area rivers, expect to see several rivers crest at near-record flood levels. Sea Surface Temperatures (SSTs) are near average over the Gulf of Mexico, which will keep the amount of moisture available to this week's storms lower than would be the case if SSTs were unusually warm. However, the cut-off low has tapped into a moisture source in the deep tropics over the Eastern Pacific where SSTs are record warm. An "atmospheric river" of water vapor can be seen on satellite images extending from the record-warm waters south of Mexico directly into the Southern U.S. (Figure 3.) This warm, moist air will be very unstable, helping contribute to severe thunderstorms with a few tornadoes over the Southern U.S. today through Thursday. As of noon EST Tuesday, one tornado had been reported in Texas, along with fourteen reports of severe thunderstorm winds.

Figure 3. Satellite-derived Integrated Water Vapor (the total amount of rain, in centimeters, that would result from condensing all water vapor in a column of air) as of 8:55 am EST March 8, 2016. Two "atmospheric rivers" of water vapor are seen affecting the U.S.--one from the Eastern Pacific flowing across Mexico into the Southern U.S., and one extending from the tropics past Hawaii towards the coast of California. Image credit: NOAA/ESRL.

Figure 4. Predicted precipitation for the 3-day period ending 7 am EST Friday, March 11, 2016. Image credit: National Weather Service.

Jeff Masters

Climate Summaries Flood

Moisture at Last for California; Severe Storms, Heavy Rain for TX/LA/AR/MS

By: Bob Henson , 6:57 PM GMT on March 07, 2016

Rain lovers across central and northern California--and snow lovers across the Sierra Nevada--were equally pleased at the storminess that enveloped the region over the last several days. Multiday rainfall totals of 1” to 4” were widespread across the Bay Area, with larger amounts toward the north and at higher elevations. Several points along the Coast Range racked up 10” to 12” totals. Snowfall was also generous across the Sierra Nevada mountains to the east (see below). All told, the weekend storms gave a big boost to a region that had gotten only scant precipitation during February--usually one of the wettest months of the year, and often a prodigiously stormy month during strong El Niño events, such as the one now in place. The precipitation wasn’t as abundant toward Southern California, but even this drought-scarred area got an encouraging dose of precipitation during the weekend and into Monday morning.

Figure 1. Webcam photo of snow atop Frazier Mountain in far northern Ventura County, CA, on Monday morning, March 7, 2016. Image credit: NWS/Los Angeles.

Figure 2. WunderMap interactive radar shows a line of intense thunderstorms moves across the San Diego/Tijuana area at around 9:15 am PST on Monday, March 7, 2016.

Thunderstorms raged off the southern California coast on Sunday night, producing ample lightning and paving the way for a dark and stormy Monday morning over coastal Southern California. Several potent lines of thunderstorms moved across the region’s coastal metropolitan areas, bringing lightning, hail, and brief heavy rain. Severe thunderstorm warnings were in effect for most of San Diego County as one line approached.

Sierra snowpack clawing its way back toward average
The crucial Sierra Nevada snowpack, which stores about a third of the water used by Californians, has improved over the last few days. As of Sunday, March 6, the Sierra Nevada had pushed back above its long-term average values for accumulated precipitation in the water year to date, starting July 1 (see Figure 3). A good portion of that moisture has run off or melted off, helping to replenish downstream reservoirs and aquifers. The actual amount of water held in the snowpack--the snow water equivalent--is between about 75% and 85% of average for the wet season to date, according to daily analysis from the California Department of Water Resources. With several storms still in the pipeline over the next few days, that percentage is likely to climb.

Figure 3. Precipitation totals for the three regions of the Sierra Nevada from July 1 through March 6 (green bars), compared to the last four years (tan, grey, yellow, and red bars) and to average long-term values for the same period. Image credit: Jan Null, Golden Gate Weather Services.

L.A. still lacking; Seattle still soaked
Even after this weekend’s storms, Southern California remains on the low side when it comes to 2015-16 winter precipitation. As of midnight Sunday night, Los Angeles had racked up 0.64” for the month, with another half inch or so on Monday morning. Yet the total through Sunday night of 5.64” remained far below the average wet-season total to date (October 1 – March 6) of 11.61”. As of midnight Sunday, San Diego had garnered just 0.33” of rain this month. That left its total since October 1 (3.91”) almost 7” below the average rainfall received by this point in the year. Additional rain on Monday will help, but it appears that the bounty of heavy rain over the next week-plus will be aimed primarily north of the LA-San Diego area, with the possible exception of another weekend storm around Friday/Saturday. On the plus side, there remains a chance of additional rain heading toward the region over at least the following week or so, as more impulses travel along the subtropical Pacific jet stream.

Most folks in Seattle would probably be happy to see the El Niño rain belt focusing further south. The winter of 2015-16 is already the wettest in Seattle’s 123-year weather history--an utterly unexpected result during a strong El Niño year--and the downpours show no sign of abating. As of Sunday night, Sea-Tac Airport had racked up 39.44” of moisture in the wet season that began on October 1, 2015. Measurable rain has occurred at Sea-Tac on each of the first seven days of March. The only time March began in Seattle with a longer streak of rain was March 1-8, 1919. That record appears likely to tumble, as there is rain in Seattle’s forecast every day this week.

Figure 4. The 500-mb forecast from the 12Z Monday run of the GFS model, valid at 72 hours (12Z or 7:00 am EST Thursday, March 10), shows a deep, slow-moving upper low centered over southern Texas, with a strong, warm ridge over the northeast U.S. Image credit: Levi Cowan,

Severe weather, heavy rain still heading for south-central U.S.
The powerful upper jet plowing across California this weekend will soon carve out an unusually deep upper low extending far south into Mexico. Near-record low temperatures (especially cool daytime highs) can be expected across northern Mexico, with snow falling atop some of the higher Sierra Madre peaks. The upper low will help channel copious amounts of tropical moisture northward into the south-central U.S., setting the stage for a multi-day period of torrential rain and severe weather. With the atmosphere so moist at all levels, and with upper- and lower-level winds all blowing more or less from the south, this doesn’t look like a classic spring outbreak with isolated supercell thunderstorms. Instead, we’re likely to see many clusters and lines of intense storms dumping extremely heavy rain, with some severe weather embedded in the mix. Short-lived circulations and brief tornadoes may crop up as the storms multiply, making for a tough week for local forecasters. As of midday Monday, the NOAA Storm Prediction Center was not highlighting any areas of significant severe weather for the next several days, another sign that most of the storms are unlikely to be especially destructive. For most areas, SPC is dubbing the event a “long duration-low probability tornado risk.”

Figure 5. Convective outlooks issued by NOAA’s Storm Prediction Center as of midday Monday, valid for the 24 hours until 6:00 am CST on (left to right) Tuesday, March 8; Wednesday, March 9; and Thursday, March 10.

The very moist air mass expected to flow into the south-central states will approach or exceed precipitable water records for March at some locations. Together with the powerful upper low, this means the potential for extreme rainfall, gradually spreading from Texas and Arkansas into Louisiana and Mississippi as the week unfolds. The details will depend on how each night’s showers and thunderstorms evolve; it’s likely that the zones of highest rainfall will get shunted southeastward each day as rain-cooled air pushes a surface front in that direction. When all is said and done by week’s end, we may see totals of more than a foot of rain in some locations, with widespread 6-12” amounts.

Bob Henson

Figure 6. 7-day precipitation forecast for the period from 12Z (7:00 am EST) Monday, March 7, though Monday, March 14, 2016. Image credit: NOAA/NWS Weather Prediction Center.

Extreme Weather

El Niño-Related Rains Take Aim on California--and Arkansas

By: JeffMasters, 2:19 PM GMT on March 04, 2016

The Pacific wave train set to bring a much-anticipated storm to the West Coast this weekend looks like it has a second destination in mind. Parts of the south-central U.S., especially Arkansas, are in line for what could be some of their heaviest March rains on record next week, once the Pacific storm cuts off and settles in for a spell.

Lower-elevation rains and mountain snows will push inland on Friday and Saturday from Washington to central California as the powerful Pacific jet stream slams into the coast. Initially, snow levels will be on the high side across the Sierra Nevada--above 7000 feet on Saturday--but as colder air filters in, the snow level will drop to the 3500-5000 foot range, which is good news for replenishing the critical Sierra snowpack. Many parts of the Sierra will receive one to two feet of snow by Monday, with even more across the higher peaks. As the jet stream continues plowing inland, a second wave at its base should goose the rains and mountain snows across southern California, which has missed out on many of this winter’s wet storms. Coastal SoCal can expect widespread 1-2” amounts, with 2-4” possible in the San Francisco Bay area.

Figure 1. The latest weekly U.S. Drought Monitor shows that as of March 1, more than 38% of California remains in exceptional drought (D4, the worst category). This is only marginally better than the 40% coverage from one year ago this week. Some improvement can be expected over the next week or two. Image credit: National Drought Mitigation Center.

The Los Angeles area needs more than 6” of rain just to catch up to what an average wet season would have produced by now, much less a strong El Niño winter. In a blog post late Thursday, Daniel Swain (California Weather Blog) was cautiously optimistic: “…it appears increasingly likely that March will at least be able to make a dent--even though it’s quite clear that California’s multi-year drought will persist through the summer.”

The follow-up storm for late next week that we discussed in our Wednesday post isn’t looking quite as potent in recent model runs, but as Swain noted, “Present model solutions still suggest a storm that would be quite impressive by the low standards set during recent drought winters.”

Figure 2. Rainfall projected for the 7-day period ending at 7:00 am EST Friday, March 11, 2016. Image credit: NOAA/NWS Weather Prediction Center

Next stop: Southern Plains
In classic El Niño fashion, the Pacific jet stream will dip to uncommonly low latitudes as it move inland. By midweek, the jet will have carved out an upper-level low in northern Mexico (see Figure 3 below). At that point, its progress will be halted by strong upper ridging over the eastern U.S. In between, this will allow for extremely rich tropical moisture to flow northward from the Caribbean and Gulf of Mexico into the lower Mississippi Valley. The amount of precipitable water in this air mass is projected to surpass record levels for March in some areas.

A stationary front expected to lie from Texas toward Illinois will become the focus of multiple rounds of heavy showers and thunderstorms over several days. Some severe weather could emerge, including tornadoes, although the set-up looks less like a prolific twister producer and more like a torrential rainmaker. The focal point is likely to be Arkansas, where the stationary front should be aligned near or just east of the Ozarks. This would help enhance uplift and set the stage for what could eventually pose a serious flooding threat. The 00Z Friday run of the GFS model dumped 8” to 12” of rain over most of the southeast half of Arkansas over the ten days ending on Sunday, March 13. A secondary peak of 8" or more could develop in parts of Louisiana. Such a forecast is quite plausible, given the very moist air mass expected and given the fact that upper-level lows often move even more slowly than expected. March is the most common month for river floods across the southeast U.S., and heavy spring rains are a hallmark of El Niño in this region.

In records going back to 1876, Little Rock, AR, has never seen a March with more than 10.43” of rain (set in 1897). If the ingredients come together as models suggest, Little Rock could approach that record before the month is even half over.

Figure 3. WunderMap depiction of upper-level flow at the 200-mb level (around 34,000 feet) from the 0Z Friday GFS model projection valid at 10:00 am EST Thursday, March 10. Wind speeds are shown in knots; multiply by 1.15 for mph.

Mexico could also see unusual weather next week as the strong upper low dives into place. An upper-level trough extended far into Mexico during mid-December 1997, near the peak of the “super” El Niño of 1997-98. That month brought Guadalajara its first snowfall since 1881 and Monterrey its first snow in 30 years. Next week’s upper-level low may be even stronger over northern Mexico than the one in December 1997. Lower-level temperatures won’t be as cold with this event, now that it’s early March, but at least some dabs of higher-elevation snow are possible.

Bob Henson

PS from Jeff and Bob: Last call for blog-name suggestions!
We’ve had great fun sifting through more than 100 potential new names for this blog submitted in the comments section for last Friday’s post. As we explained, we’re renaming the blog to better reflect our joint authorship. The ideal would be a cool, pithy name that reflects the spirit of the blog in covering both weather and climate, with particular emphases on tropical meteorology, severe weather, and climate change. Our full names will serve as a subtitle, so they needn’t be part of the new blog name. Please feel free to chime in with your suggestions in the comments section of this post, or in last Friday’s post. If you’re a WU member, you can drop us a line via WU Mail. All suggestions made by March 10 will be considered. Thanks again for your creativity and enthusiasm--it is much appreciated!

Figure 4. A word cloud produced by using the titles of all 3200-plus entries posted to this blog since it was launched in 2005. Image credit: Dr. Jeff Masters.

El Niño Extreme Weather

El NIño’s Long-Awaited Grand Performance Is On Its Way to California

By: Bob Henson , 6:07 PM GMT on March 02, 2016

After a crushingly dry February, it looks as if early to mid-March is likely to bring California some of the serious moisture it needs from the 2015-16 El Niño event--and perhaps some unwanted flooding and mudslides. Long-range models are increasingly confident that the low-latitude jet stream that’s been dodging the California coast for weeks will finally plow into the state over the next 10 to 15 days, hauling copious amounts of Pacific moisture inland with it. The last few runs of the GFS and ECMWF models have become especially bullish on the development of one or two atmospheric rivers (ARs) heading into California over the next week or two. Roughly 30% to 50% of annual precipitation in the West Coast states occurs from just a few AR events per year.

The first significant storm should plow into northern and central California this coming weekend, followed by a stronger series of storms affecting most of the state during the following week. The 0Z Wednesday operational run of the GFS model doused parts of the central and northern California and Sierra Nevada with 10” to 20” of precipitation over the ten-day period ending at 7:00 pm EST Friday, March 11. The GEFS and ECMWF ensembles, though less dramatic than individual runs, still paint a very wet picture for the state. It remains unclear how far into southern California the biggest rains and mountain snows will extend. The outlook for very heavy precipitation is a bit more confident from central California all the way north to Washington. Already, some California reservoirs are releasing water: though this may seem odd while the region is still in drought, it’s a long-employed strategy to help reduce the odds of flooding when torrential rains are predicted.

The stormy weather is coming just in time for the close of the El Niño Rapid Response Field Campaign being conducted by NOAA’s Earth System Research Laboratory. The project includes flights from a NOAA Gulfstream IV hurricane-hunting aircraft, as well as hundreds of radiosonde and dropsonde launches profiling the remote Pacific atmosphere. An extra week has been added to the project’s flight schedule, which will now run through March 10. See our blog post from January 12 for more on this project.

Figure 1. The 7-day forecast for precipitation from 12Z (7:00 am EST) Wednesday, March 2, 2016, through Wednesday, March 9. Another round of intense precipitation may also affect California late next week, just beyond the range of this forecast. Image credit: NOAA/WPC.

With a little help from the MJO
The Madden-Julian Oscillation can be credited, at least in part, for the precipitation prospects over California. This recurrent cycle of tropical showers and thunderstorms has an active phase that has recently pushed eastward to the eastern Pacific, with a suppressed phase on the opposite side of the global tropics, over the Maritime Continent. Acting in tandem with the state of El Niño itself, the active MJO phase will enhance the moisture available to be drawn from the tropics into the subtropics, where the juicy air can be entrained into midlatitude storms and any atmospheric rivers approaching California. By later in March, when the active phase has moved to the Maritime Continent, a suppressed phase should follow on its heels over the eastern Pacific. “This could temper the favorable intraseasonal/seasonal state that drives California precipitation,” said Michael Ventrice (The Weather Company). As a result, West Coast rains and mountain snows may well decrease again in the latter half of March, at least for a week or two.

Figure 2. Integrated water vapor transport (IVT) projected to be heading toward California by the 00Z Wednesday GFS model run at 00Z Sunday, March 6 (7:00 pm EST Saturday). IVT incorporates the amount of moisture in the atmosphere as well as how quickly it’s moving. The channel of moisture heading toward central California includes IVT of greater than 750 kg/m/s. IVT is used by many researchers and forecasters to identify and track the evolution of atmospheric rivers. Image credit: NOAA/ESRL.

The flop that was February in California
Only a month ago, there was good reason for drought-stricken Californians to believe that the state was on its way to at least partial recovery after four years of punishing drought. Several major storms had pushed snowpack just above the seasonal average in the crucial Sierra Nevada range, which supplies about a third of the state’s water supply through snowmelt. The hope was that February and March would consolidate these early gains with at least a few more wet-but-not-damaging storms.

Then came February--a disappointingly dry month for any winter, much less an El Niño one. The month was dominated by an upper-level ridge that blocked Pacific storms and allowed temperatures to hit record levels beneath clear, sunny skies. It wasn’t quite the winter-long Ridiculously Resilient Ridge that marked the last couple of years, but it was enough to tamp down the modest precipitation surpluses across many areas. Most parts of the state got only a paltry 10-20% of average precipitation in February, as noted by Jan Null (Golden Gate Weather Services). Four major cities--San Diego, Los Angeles (Downtown), Sacramento (Executive Airport), and San Jose--saw their warmest February on record. By month’s end, the Sierra snowpack had dwindled to 85% of its typical water equivalent for the date.

What’s especially striking is how the November-to-February period turned the West Coast precipitation pattern typical of strong El Niño events on its ear. Seattle gets about twice the moisture of Los Angeles between November and February in an average year--roughly 21” vs. 10” (see Figure 3). Strong El Niño events tend to boost LA’s rainfall substantially, with little effect on Seattle’s. This time around, Los Angeles netted just 4.54” from November through February, while Seattle racked up an amazing 32.91”. In fact, by some measures, Seattle is having the wettest winter in its history, and even more heavy rain is on the way (see Figure 1 above). WU weather historian Christopher Burt takes a closer look at the precipitation to date across California in his latest post.

Figure 3. November-February precipitation totals for Seattle, San Francisco, and Los Angeles for each of the El Niño seasons classified as “strong” or “very strong” by NOAA since 1950. Image credit: Christopher Burt.

What kept the rain away?
It’s not uncommon to get a two- or three-week break between winter storms over California, especially toward the south, but the duration of the February mini-drought in the midst of a powerful El Niño was a puzzler for experts and everyday Californians alike. Data gathered throughout the month by NOAA’s field project may help shed light on what happened. One obvious factor: a change in the equatorial showers and thunderstorms (convection) that typically lead to El Niño impacts on a broader scale. Instead of the convection shifting to the eastern tropical Pacific, as is typical during a strong El Niño, most of the storminess in February was centered over the central Pacific. The downstream effects of this dislocation likely played a role in the West Coast ridging and the dearth of major California storms.

Figure 4. Sea surface temperatures (relative to seasonal average) for February 15, 1998 (top) and February 15, 2016 (bottom). Image credit: NASA.

Along with the displaced convection, the west-to-east gradient in sea-surface temperature across the tropical Pacific has been substantially weaker than it was during other strong El Niño events of modern times. The eastern tropical Pacific has been plenty warm: sea surface temperatures in the crucial Niño3.4 measuring region were 3.1°C (5.6°F) above average in the week of November 18. That’s the warmest weekly departure in NOAA records going back to 1990. What’s been absent, for the most part, is the horseshoe-shaped region of cooler-than-average water that typically cradles the west end of the El Niño equatorial warming, extending from Indonesia toward the northeast and southeast (see Figure 4, top, from February 1998). “These anomalies just never materialized, perhaps due to the background warming trend, or some other currently unknown reason,” said Klaus Wolter (NOAA/ESRL).

Likewise, the east-to-west trade winds across the tropical Pacific have not weakened or reversed as much as in previous strong El Niño events. “In January 1983 and 1998, it was very cool west of the Date Line, especially in the Northern Hemisphere,” pointed out Kevin Trenberth (National Center for Atmospheric Research). “This year it’s at least 1°C warmer. The gradients along the equator are much less. So the reversal in the trade winds is nowhere near as extensive or as strong as it was in those two events.”

All of these factors have thrown sand in the cogs of the El Niño machine, cutting back on its ability to synchronize ocean and atmosphere across the tropical Pacific. “Every El Niño has its own character and gets modulated by other effects,” Trenberth noted. Despite its idiosyncrasies, the El Niño machine of 2015-16 is far from broken right now. Although the West Coast response to this El Niño hasn’t followed the playbook, many other parts of the world have seen prototypical El Niño conditions over the last few months. These include:

Drought, fires and severe air pollution over Indonesia late last year
—A reduced summer monsoon over India, plus catastophic autumn rains in far southeast India (both consistent with El Niño)
Increasing heat and drought across northeast Brazil, along with significant drought relief over the hard-hit Sao Paolo region
—The exacerbation of a severe multiyear drought in southern Africa
—Warmer-than-average winter temperatures across Canada and the northern U.S. (in fact, virtually all of the contiguous U.S. saw a warmer-than-average winter)
—Wet conditions and enhanced severe weather across the Gulf Coast and Florida

Figure 5. The mean value of model-generated departures from average precipitation for each month from November through April during strong El Niño events. The maps are based on an ensemble of 130 simulations of weather from 1979 to 2014. Image credit: Andrew Hoell, NOAA/ESRL.

It’s the whole wet season that counts
Ever since last autumn, when it became clear this El Niño was likely to be among the biggest on record, experts warned not to expect an entire winter chock-full of heavy rain over California. Seasonal forecasts from the NOAA Climate Prediction Center trended toward a wet winter, to be sure, but they were amply caveated with the small but real chance that precipitation could wind up below average. The importance of El Niño’s strength in determining the California outcome was highlighted in a paper published this winter in Geophysical Research Letters. To get around the problem of small sample size, lead author Andrew Hoell (NOAA/ESRL) and colleagues classified each winter from 1979 to 2014 based on its Niño3.4 temperatures through that period. Then they simulated the weather over that 35-year period a total of 130 times, using three different models primed with the actual evolution of SSTs, sea ice, greenhouse gases, and ozone. The resulting ensemble thus offered 130 different takes on how a given series of El Niño events might influence California rain and snow.

Not too surprisingly, strong El Niño events are most likely to make California wet. During a strong event, the study found that Northern California is roughly five times more likely to get a winter with 150% of average precipitation, with a near-zero chance of getting less than 50% of average. The less intuitive outcome is that moderate and weak El Niños showed only a small (and less reliable) ramp-up in average precipitation. In southern California, the effect of a strong El Niño was even greater: for such events, the models showed a near-zero chance of getting less than 75% of normal November-to-April precipitation.

If it were to stay most dry in southern California this March and April, that near-zero chance would become a reality. However, it appears that March is just as climatologically likely as any other month to produce a bumper crop of rainfall relative to average across the region during a strong El Niño (see Figure 5 above). There is still plenty of room for a “Miracle March” to boost the entire water-year outlook, as this month just might manage to do.

We’ll be back with our next post on Friday.

Bob Henson

Figure 6. Panorama of the scanning X-Band radar installed in San Francisco in support of the NOAA 2016 El Niño Rapid Response Field Campaign Image credit: Francesc Junyent, CSU/CIRA.

Figure 7. Participants confer at NOAA’s Earth System Research Laboratory in Boulder at a daily forecast briefing for the NOAA 2016 El Niño Rapid Response Field Campaign. Image credit: Barb DeLuisi.

El Niño Extreme Weather

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Category 6™


Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather