Category 6™

Food System Shock: Climate Change's Greatest Threat to Civilization

By: Jeff Masters , 4:00 PM GMT on April 29, 2016

The greatest threat of climate change to civilization over the next 40 years is likely to be climate change-amplified extreme droughts and floods hitting multiple major global grain-producing "breadbaskets" simultaneously. A "Food System Shock" report issued in 2015 by insurance giant Lloyds of London outlined a plausible extreme shock to global food production that could cause rioting, terrorist attacks, civil war, mass starvation and severe losses to the global economy. Their scenario, which Lloyds gave uncomfortably high odds of occurring--significantly higher than 0.5% per year, which works out to at least an 18% chance of occurrence in the next 40 years--goes like this:

A strong El Niño event develops in the equatorial Pacific Ocean. Severe drought typical of El Niño hits India, eastern and southeastern Australia and Southeast Asia, causing the following crop losses (note that wheat, rice and corn make up over 50% of all agricultural production world-wide):

India (world's #1 rice and #7 wheat exporter): wheat -11%, rice -18%
Vietnam (world's #2 rice exporter): rice -20%
Australia (world's #3 wheat exporter): wheat -50%
Bangladesh, Indonesia, Thailand, Philippines: rice -6% to -10%

Historic flooding hits Mississippi and Missouri rivers, reducing production of corn in the U.S. by 27%, soybeans by 19% and wheat by 7%. Nepal, Bangladesh, northeastern India and Pakistan see large crop losses due to torrential rainfall, flooding and landslides, with Pakistan losing 10% of their wheat crop.


Figure 1. Historic flooding on the Missouri River on July 30, 1993, just north of Jefferson City, Missouri. Midwest floods in 1993 caused a 33% loss in U.S. corn production. Image credit: Missouri Highway and Transportation Department.

On top of the adverse weather, global crops are attacked by two major diseases: Asian soybean rust and Ug99 wheat stem rust, which cause additional 5 - 15% crop losses in Argentina, Brazil, Turkey, Kazakhstan, Ukraine, Pakistan and India. The extreme weather/plant disease double whammy causes global corn production to drop by 10 percent, soybeans by 11% and rice by 7%. Wheat, corn and soybean prices spike to quadruple the levels seen around 2000. Rice prices quintuple as India buys from smaller exporters following restrictions imposed by Thailand. Food riots break out in urban areas across the Middle East, North Africa and Latin America. The euro weakens and the main European stock markets lose 10% of their value; the U.S. stock markets lose 5% of their value. The scenario mentions the possibility of civil war in Nigeria, famine threatening to kill one million people in Bangladesh and Mali becoming a failed state. Terrorist attacks in the U.S., in combination with concerns over heightened military tensions between Russia and NATO, plus conflict between India and Pakistan, cause major stock market losses.


Figure 2. Tourists wear protective face masks as they walk along the Red Square in Moscow, Russia on Aug. 6, 2010. Moscow was shrouded by a dense smog that grounded flights at international airports and seeped into homes and offices, due to wildfires worsened by the city's most intense heat wave in its history. The heat wave and fires during the summer of 2010 killed over 55,000 people in Russia and decimated the Russian wheat crop, causing global food prices to spike. (AP Photo/Mikhail Metzel)

A historical analogue: the extreme weather of 2010
The extreme weather of the year 2010--which I speculated was Earth’s most extreme weather year since the famed “Year Without a Summer” in 1816-- showed us that multiple extreme weather events in major grain-producing areas can indeed cause dangerous shocks to the global food system. This was unexpected at the beginning of 2010, when in its January World Agricultural Supply and Demand Estimates report, the U.S. Department of Agriculture predicted higher global wheat production and lower prices for 2010 - 2011. But extreme weather began a dramatic assault on the world's grain-producing nations in the spring of 2010, when record rainfall in Canada, the world’s second-largest wheat exporter after the United States, cut Canada’s wheat harvest by 14%. As spring turned to summer, the jet stream got "stuck" in an unusual loop that kept cool air and rain-bearing low pressure systems to the north and east of Russia, bringing Pakistan their costliest floods in history and a 12% decline in their wheat production. The "stuck" jet stream pattern allowed a titanic heat wave and extraordinary drought to envelop Russia and Ukraine; Moscow's all-time heat record was equaled or exceeded five times in a two-week period. Over a thousand Russians seeking to escape the heat drowned in swimming accidents, and thousands more died from the heat and from inhaling smoke and toxic fumes from massive wild fires. In all, 55,736 people died in the heat wave--the second deadliest in recorded human history, behind the European heat wave of 2003 (77,000+ deaths). Wildfires in Russia in 2010 scorched more than 1 million hectares, 25% of crop production was lost, and economic losses reached $15 billion--1% of Russian GDP. The drought slashed the wheat harvest by 33% and damaged soils to such an extent that 10% of Russian wheat fields could not be planted in 2011. Russia--the world’s fourth-largest wheat exporter accounting for roughly 14% of the global wheat trade--responded by imposing an export ban on wheat, barley, and rye, as fears of domestic price spikes or shortages increased. Neighboring Ukraine, the world's 6th largest exporter of wheat, saw an 18% decline in their wheat harvest due to extreme drought, heat, and wildfires, and cut wheat exports by 54%.


Figure 3. Tunisians carrying loaves of bread shout slogans 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. Image credit: MARTIN BUREAU/AFP/Getty Images.

The impact: wheat prices double; food riots erupt
As a result of the global extreme weather during 2010, the price of wheat more than doubled from approximately $4 per bushel in July 2010 to $8.50 - $9 in February 2011. These price increases hit the nations of the Middle East and North Africa particularly hard, since they import more food per capita than any other region of the world, due to their scarce water supplies and lack of farmable land. According to a 2013 report, "The Arab Spring and Climate Change"--issued by the Center for American Progress, the Stimson Center, and The Center for Climate and Security--the top nine importers of wheat are all in the Middle East; seven had political protests resulting in civilian deaths in 2011, and the food price increases were identified as a major contributing cause of the societal unrest.

The Lloyds food shock scenario: at least 18% likely in the next 40 years?
Fortunately, many of the extreme weather events envisioned in the Lloyds scenario did not come to pass in 2010: drought in India, drought in Australia, and record flooding in the United States. However, many historical extreme weather events have caused the type of crop losses envisioned in the Lloyds scenario--they just haven't all hit at the same time. The main key to realizing the Lloyds scenario is to have an extreme weather event in the U.S. that causes a major failure of the corn crop, since the U.S. accounts for 40% of global corn production and 50% of global corn exports (FAOSTAT, 2013). The U.S. has seen four extreme weather events over the past 40 years that have caused at least a 25% drop in the production of corn (this is on par with the 27% drop given in the Lloyds scenario):

1983 (drought and economic recession caused a 49% loss in corn production)
1988 (drought caused a 31% loss in corn production)
1993 (Midwest floods caused a 33% loss in corn production)
1995 (heat waves and a corn borer infestation caused a 26% loss in corn production)

A second key to realizing the Lloyds scenario is to have additional significant crop-destroying extreme weather events in at least two other major grain-producing areas. One good candidate would be India, since it is the world's top rice exporter. Over the past 40 years, there have been five droughts in India that have caused at least a 10% decline in India's rice crop, with the worst being the 23% drop in 2002 (the Lloyds scenario envisioned an 18% drop in Indian rice production.) Another good candidate for an extreme weather food system shock event would be a drought in Australia, the world's #3 exporter of wheat. Australia has experienced eight droughts over the past 40 years that have caused at least a 25% loss of wheat production; the worst was in 2002, which caused a 58% decline in wheat production (the Lloyds scenario envisioned a 50% drop in Australian wheat production.)

Now let's do some rough math. Using the past 40 years as a guideline, we'd need to see the 10% chance of a U.S. event, the 20% chance of an Australian event, and the 12% chance of an Indian event all hit in the same year. Multiplying together those probabilities gives a 0.25% chance of the Lloyds scenario happening in a given year--something we would expect to happen only once every 400 years. One could argue that on top of all this would be needed a major crop disease outbreak--potentially making the Lloyds scenario a 1-in-1000 year event or rarer. However, we wouldn’t need the exact locations for the non-U.S. extreme weather specified in the Lloyds scenario--specifically, India and Australia--to occur in order to get devastating global impacts. A serious drought in Europe, China, or South America could just as easily combine with a U.S. event to cause the impacts of the Lloyds scenario to verify. Therefore, my rough estimate is that the Lloyds scenario is in the 1-in-100 to 1-in-200 year probability range. A 1-in-200 year event that has a 0.5% chance of happening in a given year has an 18% chance of happening when summed up over a 40 year period: 100 - 100*(.995)^40 = 18%. Lloyds itself says the odds of a scenario like it outlines coming to pass are "significantly higher" than 1-in-200. If we assume the Lloyds scenario has a 1% probability of happening in a given year--a 1-in-100 year event--there is a 33% chance of such an event happening at least once over a 40-year period.


Figure 4. Proportion of the total calories coming from the main four commodity crops (corn, wheat, rice and soy) by country. The U.S., China, and India are the world leaders. Major crop-damaging droughts or floods hitting all three nations simultaneously would be a major blow to the global food system. Image credit: UK-US Taskforce on Extreme Weather and Global Food System Resilience, 2015.

The Lloyds scenario will be increasingly likely in coming decades
Unfortunately, a serious shock to the global food system will grow increasingly likely in the next few decades. According to an independent 2015 food shock study by the UK-US Task Force on Extreme Weather and Global Food System Resilience, the odds of an extreme weather food shock capable of reducing the production of corn, soybean, wheat and rice by 5-7% will grow from 1% per year to over 3% per year by 2040. The increased vulnerability will occur due to climate change, population growth, decreasing water availability, the alarming reduction in plant-pollinating insects like bees, loss of topsoil and a shift towards more meat consumption globally. About 805 million people worldwide are undernourished, according to the United Nations, and this number will grow as the population increases from 7.3 billion now to a projected 9.6 billion by 2050--mostly in Africa and other developing regions. The Food and Agriculture Organization (FAO) projects that global agricultural production will need to more than double by 2050 to close the gap between food supply and demand. Water scarcity, due in part to unsustainable pumping of groundwater resources for agriculture, is accelerating at such a pace that two-thirds of the world’s population could live under water stress conditions by 2025. While an increase in heat and carbon dioxide will benefit crops in some areas, scientists believe climate change will have a net negative effect overall on crop yields and fisheries in the future. Plant diseases and insect damage are also expected to greatly increase in a warmer climate. In the four largest rice producing countries--China, India, Bangladesh, and Thailand--insects currently cause a loss of 10- 20% of the crop, and this is expected to increase to 20 - 30% by 2100. These nations have 40% of the world's population, and make 60% of the world's rice. For corn, the world's four largest producers--the U.S., China, France, and Argentina--are expected to see insect pest losses double from 6% to 12%. The story is similar for wheat; pest losses are expected to double from 10% to 20% by 2100.


Figure 5. The global price of food between 1990 - January 2016, as measured by the U.N.'s FAO Food Price Index. The FAO Food Price Index is a measure of the monthly change in international prices of a basket of food commodities. It consists of the average of price indices for Cereals, Oils and Fats, Sugar, Dairy, and Meat, weighted by the average export shares of each group. Food prices between 2002 - 2004 are given a benchmark value of "100". Thanks to the Russian drought of 2010, global food prices in early 2011 were the highest since the food crisis of 1972 - 1974. Food prices have decreased in the past few years due to good harvests, though. Image credit: Food and Agriculture Organization of the United Nations.

The Lloyds scenario is less likely than usual this year
The odds of the Lloyds scenario coming true in 2016 are probably lower than average, fortunately, even though we just came out of a strong El Niño event like envisioned in the scenario. The current El Niño event did lead to record flooding in the Midwest U.S. in December, but NOAA's 3-month flood outlook does not call for any major flooding in the primary crop-growing areas of the U.S. this spring, thanks to a relatively meager snowpack in the Upper Midwest left by a mild winter. The 2015 El Niño did cut precipitation in India by 14% in their summer monsoon, but this led to just a 1% decline in their rice production and 7% decline in wheat; the Lloyds scenario envisioned 18% and 11% declines in these crops, respectively (though drought continued in India as of April 2016, with over $600 million in agricultural damages so far in January - March 2016.) Food prices entering 2016 were at a ten-year low, making an extreme weather food price shock less likely than was the case in 2010, when food prices were already high. Still, I have become increasingly mistrustful of the stability of our climate in recent years. Record-warm temperatures far exceeding anything in recorded history have affected the globe over the past three months, and this record heat may lead to some incredible extreme weather events unparalleled in human memory this summer. In its April 2016 forecast, the usually reliable European model predicted a very hot summer in the grain producing areas of the Midwest United States. This forecast was even hotter than the model's April 2012 forecast for the summer of 2012, which ended up being the second hottest summer in U.S. history, with intense drought that led to crop losses exceeding $31 billion. A drought like that coupled with record drought in two other world breadbaskets could well trigger a Lloyds scenario.


Figure 6. The northward wind speed (negative values, blue on the map, indicate southward flow) at an altitude of 300 mb in the mid-latitudes of the Northern Hemisphere during July 2011 and July 1980. July of 2011 featured an unusually intense and long-lasting heat wave in the U.S., and the normally weak and irregular waves (like observed during the relatively normal July of 1980) were replaced by a strong and regular wave pattern. A similar extreme jet stream pattern was observed during the summer of 2010, when catastrophic drought in Russia led to a huge spike in global food prices. Image credit: Vladimir Petoukhov.

Extreme weather capable of triggering the Lloyds scenario is growing more common
If it seems like the weather in recent years has gotten crazier than you remember from 20+ years ago, you are right. As I discussed in a March 2013 post, "Are atmospheric flow patterns favorable for summer extreme weather increasing?", research published by scientists at the Potsdam Institute for Climate Impact Research (PIK) in Germany found that extreme summertime jet stream patterns had become twice as common during 2001 - 2012 compared to the previous 22 years. One of these extreme patterns occurred in the summer of 2010, leading to Russian drought that triggered the steep rise in food prices implicated in the “Arab Spring” uprisings. When the jet stream goes into one of these extreme configurations, it freezes in its tracks for weeks, resulting in an extended period of extreme heat or flooding, depending upon where the high-amplitude part of the jet stream lies. The scientists found that because human-caused global warming is causing the Arctic to heat up more than twice as rapidly as the rest of the planet, a unique resonance pattern capable of causing this behavior was resulting. This sort of jet stream behavior makes a serious extreme weather food shock event much more likely to occur, since extreme weather events affect multiple areas of the planet simultaneously for long periods of time.

I predict that the type of triple-whammy of extreme weather events capable of causing a food shock scenario similar in impact to the Lloyds scenario will increase in probability to become a 1-in-50 year event by 40 years from now--a 2% chance of happening in a given year--due to the increasingly extreme nature of the jet stream, when combined with the ongoing increase in global temperatures, drought intensity, and heavy precipitation events. This means that it is likely we will see something causing the impact of the Lloyds scenario occur in the next 40 years--a significant disruption of the global economy, intense political turmoil, war and the threat of mass famine. The nation's top scientific research group, the National Research Council, had these words of warning in their 2012 study titled, "Climate and Social Stress: Implications for Security Analysis": “expect climate surprises in the coming decade, including unexpected and potentially disruptive single events as well as conjunctions of events occurring simultaneously or in sequence, and for them to become progressively more serious and more frequent thereafter, most likely at an accelerating rate. The climate surprises may affect particular regions or globally integrated systems, such as grain markets, that provide for human well-being.” They further warned that such an event would "produce consequences that exceed the capacity of the affected societies or global systems to manage and that have global security implications serious enough to compel international response." One could argue that such an event has already occurred, as a climate change-related drought was identified as a key cause of the ongoing civil war in Syria.

There is hope that we will overcome, though. The global agriculture system has shown impressive resiliency in more than meeting the demands of a growing population over the last 50 years. The December 2015 Paris Accord--the commitment by the world's nations to de-carbonize our economies--should result in long-term changes to the global food system that should make the Lloyds scenario less likely to occur. 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.

Jeff Masters

Climate Change Drought

Joaquin, Patricia, and Erika Get Their Names Retired From the List of Hurricanes

By: Jeff Masters , 3:32 PM GMT on April 28, 2016

The World Meteorological Organization (WMO) announced last week that three tropical cyclones from 2015 would get their names retired--Hurricane Joaquin and Tropical Storm Erika in the Atlantic, and Hurricane Patricia in the Eastern Pacific. The WMO will replace Erika with “Elsa”, Joaquin with “Julian” and Patricia with “Pamela” when the 2015 lists are reused in 2021.

The two new retired names in the Atlantic brings the total number of storm names retired since 1953 to 80. Although the Eastern Pacific, on average, has more hurricane activity than the Atlantic, far fewer storms have had their names retired in the Eastern Pacific, since the prevailing steering currents tend to take the storms to the west-northwest, away from land. Patricia is just the 11th storm to get its name retired (the names Adolph and Israel were removed from the Eastern Pacific list in 2001 due to political considerations, bringing the total number of retired names in the basin to thirteen.) Prior to Patricia, Mexico's Hurricane Manuel from 2013 and Hurricane Odile from 2014 both had their names retired, making 2015 the third consecutive year a hurricane has gotten its name retired in the Eastern Pacific--an unprecedented occurrence.


Figure 1. Hurricane Patricia as seen by the MODIS instrument on NASA's Terra spacecraft at 1:30 pm EDT October 23, 2015. Five hours prior to this time, Patricia was the most intense tropical cyclone (for wind) ever observed on Earth, with 215 mph sustained surface winds and a central pressure of 872 mb. Image credit: NASA.

Earth's strongest tropical cyclone ever measured: Hurricane Patricia
Record-warm ocean waters helped Hurricane Patricia explode into a Category 5 storm with 215 mph sustained surface winds and a central pressure of 872 mb off the Pacific coast of Mexico on October 23, 2015. Hurricane Patricia's 215 mph winds officially tie it with the Northwest Pacific's Super Typhoon Nancy of 1961 for strongest winds of any tropical cyclone in world history, and Patricia's lowest pressure of 872 mb makes it the second most intense tropical cyclone in world history by pressure, behind the 870 mb measured in the Northwest Pacific's Super Typhoon Tip of 1979 (Tip's top sustained winds of "only" 190 mph were not as high as Patricia's, since Tip was a large, sprawling storm that did not have a tiny concentrated area of extreme eyewall winds.) Patricia made landfall in a relatively unpopulated area near Cuixmala in Southwest Mexico on October 23 as a Category 4 storm with 150 mph winds, killing fourteen and doing $325 million in damage. For more information, see my post, Hurricane Patricia's 215 mph Winds: A Warning Shot Across Our Bow.


Video 1. Floodwaters rage through a street on Dominica island in the Caribbean on Thursday, August 27, 2015, after Tropical Storm Erika dumped 12+" of rain on the island.

Dominica's costliest storm in history: Tropical Storm Erika
Although Tropical Storm Erika never reached hurricane strength, the storm brought a catastrophic deluge on August 27, 2015 to the Caribbean island of Dominica (population 72,000). Erika killed 30 people on the island and caused $300 million in damage--57% of their GDP of $524 million. Dominica's previous most expensive disaster was the $175 million in damage from Hurricane Marilyn of 1995. Erika is just the second Atlantic tropical storm not to reach hurricane strength to get its name retired. The other was Tropical Storm Allison of 2001, which brought record flooding to Texas, killing 41 and causing over $9 billion in damage.


Figure 2. Hurricane Joaquin as seen by the GOES-East satellite at 7:45 am EDT October 1, 2015. At the time, Joaquin was an intensifying Category 2 storm with 110 mph winds. The last position of the cargo ship El Faro, in the northwestern eyewall of Joaquin, is shown. Image credit: United States Navy and NOAA.

Hurricane Joaquin
Hurricane Joaquin was the strongest Atlantic hurricane since 2007, topping out just below Category 5 strength on October 3, 2015 with 155 mph winds. Joaquin was the second deadliest and second most damaging Atlantic named storm of 2015, causing $100 million in damage in the Central Bahamas, where it lingered for several days. Joaquin's death toll was 34, with 33 of these deaths occurring from the sinking of the ill-fated cargo ship El Faro. Although Joaquin tracked far to the east of the United States, a non-tropical low over the Southeast tapped into the hurricane's moisture, causing record-shattering rains and flooding across North and South Carolina. Several areas of South Carolina saw accumulations exceeding the threshold for a 1-in-1,000-year event. The subsequent floods inundated large areas of the state, killing 21 people and causing over $2 billion in damage.

Jeff Masters

Hurricane

A Twist to Tuesday’s Severe Weather: Tornadoes Missing

By: Bob Henson , 5:15 PM GMT on April 27, 2016

Tornado chasers scanned the skies fruitlessly on Tuesday, while residents of the Southern Plains breathed huge sighs of relief, as a bumper crop of severe thunderstorms produced buckets of large hail and high wind while spinning up only a handful of twisters. By mid-morning Wednesday, NOAA’s Storm Prediction Center (SPC) had received only five tornado reports: two in Texas, and one each in Kansas, Missouri, and Indiana. All of these tornadoes were relatively minor, with no serious damage or injury reported. High wind and large hail were far more plentiful, with more than 200 reports of each. Most of the hail was 1” to 2” in diameter, but several reports of 3” hail (larger than baseball size) came in from Marshall County in northeast Kansas. Winds gusted to 87 mph around 10:30 pm as a fierce squall line tore through Copan, Oklahoma, northeast of Tulsa.


Figure 1. Preliminary reports of severe weather received by the NOAA/NWS Storm Prediction Center for the period from 12Z (8:00 am EDT) Thursday, April 26, 2016, through 12Z Wednesday. Image credit: NOAA/SPC.


Figure 2. Lightning strikes along Interstate 70 near Junction City, Kansas, late Tuesday, April 26, 2016. Image credit: AP Photo/Orlin Wagner.


Figure 3. Susan Goodwyn holds large hail deposited by thunderstorms that swept through Wichita, KS, on Tuesday afternoon, April 26, 2016. Image credit: Susan Goodwyn/SMGPhotos via AP.


What happened to the tornadoes?
Tuesday’s outcome was far better than many residents had feared that morning, when forecasters were calling for widespread severe storms and the potential for strong tornadoes. This shortfall in tornado production wasn’t a total surprise. As we noted in Tuesday’s post, upper-level winds were not ideal for a major tornado outbreak, but it seemed plausible that adequate wind shear would accompany the extreme instability in at least a few locations that would be difficult to pinpoint well in advance. Along these lines, the large tornado watch issued for parts of Texas and Oklahoma was a PDS watch--meaning a “particularly dangerous situation,” with “several tornadoes and a few intense tornadoes likely.”

As it turned out, the upper-level winds were far from optimal during the afternoon, and by the time wind shear had improved, a squall line had formed, making it hard for any isolated supercells to develop and rotate. Thus, it was a day with high-end potential for strong tornadoes, but relatively low confidence as to how many there might be. NOAA’s midday outlook on Tuesday bore this out, with relatively low probabilities for tornadoes (maximum 10%) but much higher odds for severe hail (maximum 45%).

SPC had noted Tuesday’s potential for severe weather, including tornadoes, as far back as last Thursday, April 20. So was the forecast a bust? That depends on your perspective, and how you interpret forecaster guidance. For all time periods beyond 24 hours, the SPC convective outlooks (explained here) indicate only two things:

--the categorical risk of severe weather (from marginal to high)
--the numerical odds of getting any type of severe weather within 25 miles of any spot on the map

“Severe weather” means any or all of these:
--a tornado
--winds of at least 50 knots (58 mph), or lesser winds that inflict damage
--hail at least 1” in diameter

For Days 1, 2, and 3, the outlooks also include a crosshatched area where severe weather might be “significant”, meaning:

--a tornado inflicting at least EF2 damage
--winds of at least 65 knots (75 mph)
--hail at least 2” in diameter

With these definitions in hand, we can see that Tuesday’s outlook was far from a total bust. Figure 3 (below) shows how the outlooks issued at various lead times stacked up against the final outcome (top row, against the midday outlook issued at 12:30 pm EST Tuesday). The tornado count was undeniably low--and two of the day’s five reports were entirely outside the probabilistic risk area, associated with a bow echo across the Midwest--yet the tornado odds were relatively low to begin with, maxing out at just 10%. The hail outlook appears to verify quite well over the Southern Plains, given that about half of the 45% max-threat area (purple) experienced large hail within 25 miles. The Ohio Valley bow echo did produce more large hail than expected.


Figure 3. The progression of guidance issued by the NOAA/NWS Storm Prediction Center leading up to Tuesday, April 26, 2016. At bottom left of each panel is the lead time: Day 7 corresponds to a forecast issued six days prior (in this case, Wednesday, April 20). Day 4-8 outlooks include only the probability of any type of severe weather within 25 square miles of any point. Days 3, 2, and 1 include subjective categorization of the total risk (marginal, slight, enhanced, moderate, or high). Along the top are the Day 1 outlooks issued at 1630Z (12:30 pm EDT) Tuesday for the probability of any severe weather (left), tornadoes (center), and severe hail (right). Crosshatching indicates the forecasted possibility of significant tornadoes (EF2 or stronger) or very large hail (at least 2” in diameter). Symbols on the Day 1 outlooks along the top show actual reports from Tuesday for each category. Image credit: NOAA/NWS/SPC, courtesy James Correia (OU/CIMMS).

The question of lead time
The week-long build-up to Tuesday’s severe weather led to some soul-searching in the meteorological community: what is the value, and potential downside, of giving people five or six days’ notice that an outbreak may occur? An AP analysis by Seth Borenstein and Kelly Kissel, published on Saturday, covers the issues well. WXGeeks host and WU contributing blogger Marshall Shepherd (University of Georgia) also explored the topic thoughtfully in a Forbes essay last Thursday. (Shepherd also has some great perspective on yesterday's presumed forecast bust.]

There is some evidence that specific tornado warnings could be counterproductive if issued well in advance (such as two hours), as people may put themselves at increased risk rather than taking immediate shelter. More general outlooks, issued days ahead of time, may be a different matter. Research is still scant in this area, but long-lead outlooks could give emergency managers and response agencies extra time to raise awareness and assemble resources. Veteran atmospheric researchers such as Lance Bosart (University at Albany, State University of New York) point to the scientific accomplishments that have made such extended outlooks possible. In an email to colleagues, Bosart said:

“The achievement of being able to recognize the potential that a high-impact severe weather event will occur and where it will likely occur a week in advance is testimony to how far numerical weather prediction has advanced, how well new convection-allowing ensemble models have been integrated into the forecast process, how much probabilistic thinking has been incorporated into forecasts of high-impact severe weather events, and how well the dedicated professionals at the SPC have been able to take full advantage of these advances to produce operationally informative and useful guidance well in advance of expected severe weather outbreaks.”


Figure 4. As of mid-morning Wednesday, SPC’s convective outlooks show a slight risk of severe weather on each of Days 1, 2, and 3 (Wednesday through Friday, April 27-29, 2016).

It’s not over yet: more severe weather in the cards
With upper-level troughiness persisting in the West, and plenty of low-level moisture at hand, severe storms are a continuing possibility into this weekend. Wednesday’s threat straddles the Mississippi Valley from eastern Missouri to southern Louisiana. The day should yield mostly garden-variety severe weather, with the tornado risk quite low. More storms are possible over Texas and Oklahoma late Thursday night, with activity building on Friday as the upper-level low recharges and a warm front pushes north. Moderately strong wind shear and very high instability suggest the potential for a tornado threat worth monitoring on Friday across parts of Oklahoma and north Texas. The active pattern shows signs of continuing off and on as we roll into the first week of May and the peak of U.S. tornado season.

Bob Henson


Extreme Weather Tornado Severe Weather

Southern Plains Bracing for Potential Tornadoes, Huge Hail

By: Bob Henson , 4:45 PM GMT on April 26, 2016

Damaging tornadoes--and hailstones larger than baseballs--may crop up later Tuesday along a swath from southern Nebraska to central Texas, as a long-predicted outbreak of severe weather takes shape. NOAA’s Storm Prediction Center (SPC) has draped a moderate-risk area--the second-highest of SPC’s risk categories--from southern Nebraska into northern Texas. Despite the high confidence that widespread severe weather will occur, there remains uncertainty over exactly where the most dangerous convection (thunderstorms) will develop.


Figure 1. The NOAA/SPC outlook for severe weather issued early Tuesday morning shows a large slight risk area over the Great Plains, with increasing levels of threat centered on central KS and OK. A few severe storms are also possible across the mid-Atlantic, including the Washington, D.C., area. In its update at 11:30 am CDT, SPC extended the moderate risk area into northern Texas.


Here are some key points as of midday Tuesday:

--The strongest storms are expected in two zones: one near a warm front that will be moving slowly north across northeast Kansas and northern Missouri toward southern Nebraska, and the other along and ahead of a dry line that should be located roughly 50-100 miles west of the Dallas-Fort Worth, Oklahoma City, and Wichita areas by late afternoon.

--The vertical wind structure of the atmosphere is not ideal for a widespread tornado outbreak. Although winds do strengthen with height, and upper-level winds are somewhat stronger than expected, the upper-level storm moving into the Plains has dug far enough south that winds will have a strong southerly component at all levels. This reduces the amount of directional shear (variation of wind direction with height) that can help enhance storm rotation. In addition, storms that are moving parallel to the dry line will tend to coalesce more quickly over time, rather than being more scattered or isolated supercell storms. Still, there will be local variations in the wind profile, so tornadic supercells are a distinct possibility, including the potential for strong tornadoes. SPC's late-morning tornado outlook reflects the overall picture, with fairly low tornado probabilities spread across a large area. Models were not yet in strong enough agreement to pin down smaller areas of higher tornado probability, but those could emerge later in the day.

--Hail will be widespread, and some pockets of large hail are a near-certainty with this event, thanks to extreme instability (cold air aloft overtopping very warm, moist air at low levels). SPC expects at least a few reports of giant hailstones measuring at least 3” in diameter. This NWS reference list of hail sizes relative to common objects may come in handy. Golf-ball-sized hail is around 1.75” in diameter; baseball size, 2.75”; grapefruit size, 4.00”; and softball size, 4.50”.

--A layer of warm air several miles above the surface should serve as a cap to inhibit thunderstorm development until early to mid-afternoon. Winds above the surface should become more favorable for tornado development over time, so the longer it takes for storms to develop, the greater the risk of tornadic supercells, especially within a window from late afternoon to just after dark.


Figure 2. The high-resolution HRRR model run from 14Z (9:00 am CDT) Tuesday, April 26, 2016, projects a broken squall line to be plowing across parts of MO, KS, OK, and TX by 05Z Wednesday, April 27 (midnight Tuesday night CDT).


--High-resolution short-range models indicate that individual storms should congeal within a few hours into one or more squall lines with severe winds and large hail along the advancing dry line/cold front. This transition may occur just west, just east, or somewhere close to the DFW/OKC/Wichita corridor.

--Additional severe storms, including tornadoes, are possible on Wednesday, especially toward Arkansas and Louisiana, depending on the evolution of this squall line and how quickly the atmosphere recovers ahead of it. Another multiday stretch of severe weather is expected to start late Thursday night over north Texas and extend into the weekend, with excessive rains and flooding very possible around northeast TX, southeast OK, southwest AR, and northwest LA.

25 years ago today: the “overpass video”
Tuesday’s date has added resonance for long-time followers of U.S. severe weather. Tuesday is the 25th anniversary of a major tornado outbreak that pummeled the Southern Plains on April 26, 1991. A total of 55 tornadoes were confirmed, including an F5 twister that moved from near Wichita, KS, to demolish a mobile home community in Andover, KS, killing 13 people there. A subsequent tornado from the same supercell moved over a Kansas Turnpike overpass while a team from Wichita’s KSNW-TV were huddled beneath the girders. The resulting footage--one of the first truly viral tornado videos, even though it preceded smartphones, Facebook, and Twitter--left many with the impression that overpasses were suitable shelter from tornadic storms.


Figure 3. Overpasses are a terrible place to shelter, whether it’s attempting to shield your car from hail or to protect yourself from a tornado. Image credit: NWS/Norman, OK.


As it turns out, the KSWN team was largely lucky: the tornado that struck them was relatively weak, and many overpasses lack the girder structure that helped protect the crew. Subsequently, three people were killed near or beneath highway overpasses by tornadoes in the Oklahoma City area on May 3, 1999. The NWS now strongly advises against using overpasses as shelter, and the case for the danger of this practice is well made in this NWS slide presentation. (Needless to say, parking beneath a highway overpass on the highway to avoid hail, as shown above, is equally ill-advised, as it quickly blocks traffic and could endanger many other people.)

April 26: a date of tornadic infamy
As shown in Figure 4 below, a total of 300 tornadoes rated at least F1/EF1 have been recorded on April 26 in SPC records going back to 1954, as compiled by Harold Brooks (National Severe Storms Laboratory). These include the 1991 outbreak as well as more than 50 tornadoes on April 26, 2011--the day before the horrific 2011 Super Outbreak--and a round of tornadoes that caused 11 deaths in Oklahoma on April 26, 1984. The only dates with a larger total than April 26 are April 3 (317 tornadoes, nearly all from the infamous 1974 Super Outbreak) and April 19 (340 tornadoes, the result of major outbreaks in 1973, 1996, and 2011). The two-day total of 457 on April 26-27 is the largest for any two-day period--largely due to the 2011 Super Outbreak, whose worst day by far was April 27. Of course, tornadoes can strike on any day when conditions are favorable, and Figure 4 reveals that every date in April and May has produced dozens of twisters over the years.

Follow the severe weather on our liveblog
We will be tracking today’s events on a WU liveblog accessible from the WU front page and from this direct link.

Bob Henson


Figure 4. The number of F1/EF1 tornadoes reported on each calendar date across the period 1954 to 2015. Image credit: Harold Brooks, NOAA/NSSL; data from NOAA/SPC.

Extreme Weather Severe Weather Tornado

Busy Week of Severe Weather Ahead for Nation’s Midsection

By: Bob Henson , 4:08 PM GMT on April 25, 2016

In classic late-April fashion, the ingredients are coming into play for severe thunderstorms to prowl the central United States across several days over the coming week. The whole gamut of severe threats is likely to materialize before the week is out, from tornadoes to enormous hail, strong downburst winds, and torrential downpours. Residents of Texas and Louisiana hard-hit by flooding in recent weeks face another stretch with the potential for very heavy rain that would add to record amounts observed in the past 12 months. The storminess kicked off on Sunday with dozens of large-hail reports and at least 10 preliminary tornado reports from southern Minnesota to northern Kansas. Two storm chasers were injured, according to the Weather Channel.


Figure 1. Day 2 convective outlook issued early Monday, April 25, 2016, for Tuesday, April 26. The yellow and red colors indicate progressively higher risk for severe weather, with the red (moderate) the second-highest category.


The biggest immediate threat for tornadoes appears to be on Tuesday, when a strong upper-level storm will encounter very rich low-level moisture from Nebraska to Texas. In its early-Monday outlook for Day 2 (Tuesday), NOAA’s Storm Prediction Center placed a strip from southern Nebraska to central Oklahoma in a moderate risk of severe weather, the second highest of five risk categories. Tornadic supercells may cluster along a warm front expected to lie near the KS-NE border, and others may pop further south along a strong dryline that will advance through Kansas and Oklahoma through the afternoon and evening. A second pulse of energy rotating around the upper low will reach southern OK and north TX by late evening, possibly triggering a batch of supercells that could rage well after dark.


Figure 2. Jet-stream flow at the 250-mb level (about 34,000 feet) projected by the 06Z Monday run of the GFS model for 00Z Wednesday (7 pm CDT Tuesday). Winds at this level exceeding 90 knots (105 mph) will be nosing into southwest Oklahoma. Upward motion is enhanced where the contours separate (diffluence) and toward the front left area of highest jet-stream winds. Image credit: Levi Cowan, www.tropicaltidbits.com.


Figure 3. WunderMap depiction of CAPE (a measure of atmospheric instability) projected by the 06Z Monday run of the GFS model for 18Z (1 pm CDT) Tuesday. Just ahead of a dry line across central Kansas and Oklahoma, CAPE values of 3500-4500 J/kg (red and purple) are indicated, denoting extreme instability.

Plenty of atmospheric juice for big hail-makers
Summerlike dewpoints of 70-73°F (21-23°C) were streaming onto the Texas coast on Monday morning. This very humid low-level air mass has plenty of time to be pulled north into the moderate-risk area by Tuesday afternoon. With cold upper-level air overspreading the sultry surface air, lifted indices may get as low as -10 to -12; this would be close to the most extreme levels of instability seen in springtime tornado outbreaks across the Southern and Central Plains. The vertical wind shear (change in wind direction and/or speed with height) will also be more than adequate for tornadic storms, if not exceptionally strong. Wind speeds at 850 mb and 700 mb (about one to two miles aloft) will generally be in the 45 to 55 mph range, whereas they can sometimes top 60 mph in major tornado outbreaks. A strong “cap” (warm layer aloft) at these heights may keep storms from developing along the dry line till late afternoon or early evening. The cap will be weakest and the wind shear strongest near the warm front in northern Kansas and southern Nebraska, which is where I would expect the greatest tornado risk to evolve.


Figure 4. The National Weather Service office in Oklahoma City was warning residents Monday morning of the severe risk on Tuesday.


Given the adequate wind shear and extreme instability, there are likely to be extremely powerful updrafts in Tuesday’s storms that could produce giant hail, the size of baseballs or larger. Figure 4 shows the top-end hail risk expected in the Oklahoma City area. Large hail could extend into north Texas, where a massive hailstorm on March 16 damaged 50,000 cars and 25,000 homes, inflicting more than half a billion dollars in damage. As of April 11, the Dallas-Fort Worth NWS office had received 30 reports of severe hail for the year thus far, already the highest January-to-April total for any year in the last decade (see embedded tweet at bottom).

Looking ahead: more storms on the horizon
Tuesday’s severe weather will greatly affect the state of the atmosphere on Wednesday. As the upper-level storm and dry line push east, conditions should be generally favorable for more severe weather from eastern Missouri to east Texas, where SPC’s Day 3 outlook places a slight risk. The configuration of upper- and lower-winds suggests that the overall tornado risk may be somewhat less on Wednesday than on Tuesday.

Upper-level troughiness in the western U.S. will “reload” by late this week, as another potent upper low enters the Southwest. The Southern Plains will again be targeted for big storms around Friday, and severe weather may continue across parts of the area into the weekend, although it’s too soon to know exactly how the scenario will play out. It does appear that upper-level winds will become more meridional (flowing from south to north) toward the weekend, which would enhance the potential for storms “training” along boundaries and dumping excessive amounts of rain. NOAA’s Weather Prediction Center expects that rainfall amounts for the week starting Monday could hit 3-5” near Omaha, with a larger area of 3-7” rain projected for east Texas, southeast Oklahoma, northwest Louisiana, and much of Arkansas. Unfortunately, this coincides with some areas slammed by all-time record rainfall in March, including Little Rock, AR, and Shreveport, LA.

We’ll be back on Tuesday with an update on the severe weather threat. We are planning a liveblog as well, pending resolution of some technical difficulties that arose on Monday.

Bob Henson


Figure 5. 7-day precipitation outlook for the period from 12Z (7:00 am CDT) Monday, April 25, 2016, through 12Z May 2. Image credit: NOAA/NWS Weather Prediction Center.



Severe Weather

A WunderPhoto-graphic Salute to Earth Day

By: Bob Henson , 4:55 PM GMT on April 22, 2016

Today is the 47th annual Earth Day, a day to celebrate the beauty of the atmosphere, oceans, and biosphere of the planet that sustains us. This week I’ve had the distinct pleasure of picking a few of my favorite WunderPhotos uploaded to our website over the past year, in keeping with the Earth Day tradition established by Dr. Jeff Masters (who’s off today). The photos below are all drawn from our World View Gallery, which is updated weekly with the top WunderPhotos of the week.

Our thanks go out to all of you who have participated in making ours the largest (now 1.9 million!) and best weather photo gallery on the Internet. As someone who enjoys landscape and sky photography, I find it a never-ending treat to peruse the meteorological eye candy our members post each day. It’s also fun to see the shout-outs and high-fives that many of our photos receive in the comments section beneath each image. Thanks again for making WunderPhotos the eye-popping site that it is. Here’s to a meaningful and enjoyable Earth Day, from all of us at WU.

Bob Henson


Figure 1. On a beautiful Friday, April 15, a crew of WU volunteers trekked from the home office in downtown San Francisco to the Presidio, culling more than 100 cubic feet of invasive vegetation from the area near Mountain Lake.

Atmospheric Phenomena

Atmospheric CO2 Leaps into Uncharted Territory: 408 ppm

By: Bob Henson , 5:08 PM GMT on April 21, 2016

Even as it fades, the 2015-16 El Niño has given a big boost to the annual spring peak of carbon dioxide in the atmosphere. Preliminary CO2 data from Mauna Loa, Hawaii, for the week ending April 16 showed a concentration of 408.69 parts per million (ppm), according to NOAA. The weekly value analyzed by NOAA topped 405 ppm for the first time on March 26 (405.62 ppm), which was itself surpassed by 406.57 ppm on April 9. The one-day average concentration hit an eye-opening peak of 409.44 on April 9. That’s close to 4 ppm above any value recorded on Mauna Loa prior to this year.

“We are now witnessing the fastest growth rates of the entire record of CO2 measurements. This record-breaking growth is an expected consequence of the near record-breaking fossil fuel usage combined with the largest El Niño event in several decades.” said Ralph Keeling (Scripps Institution of Oceanography) in a Keeling Curve blog post on Wednesday. Keeling’s father, Charles David Keeling, launched the regular CO2 measurements at Mauna Loa in 1958. NOAA and Scripps now collaborate on the sampling, with slight differences in how they analyze and report the data. Scripps reported a daily value of 407.80 ppm on April 18 (see Figure 2).



Figure 1. A year’s worth of carbon dioxide concentrations measured at Mauna Loa, Hawaii, by NOAA from April 2015 through mid-April 2016. Daily averages are shown as black dots, and weekly averages as red lines. The labeled blue lines show monthly averages. Image credit: NOAA/ESRL Global Monitoring Division.


Carbon dioxide has been accumulating at an unsettling pace for some time now. Preliminary data for last year (2015) showed the biggest annual increase in CO2 concentrations of any year on record: 3.05 ppm. It was also the fourth consecutive year that CO2 levels increased by at least 2 ppm. This occurred for the first time in 1977 (just for that year) and was a rare event until the 2000s. From February 2015 to February 2016, the year-over-year increase in monthly values was 3.40 ppm, according to NOAA.

“Carbon dioxide levels are increasing faster than they have in hundreds of thousands of years,” said NOAA’s Pieter Tans in a March statement. “It’s explosive compared to natural processes.”


Figure 2. Two longer-term perspectives on CO2: the increase since 1958 measured at Mauna Loa (left), and the ups and downs produced by ice-age cycles over the last 800,000 years, as retrieved from polar ice cores. The increase of more than 120 parts per million since the mid-1800s (vertical line at far right of right-hand image) is larger than the typical difference between the frigid depths of ice ages (the dips in the right-hand image) and the relatively mild interglacial periods. Predictable variations in Earth’s orbit help trigger the onset and decline of ice ages. Image credit: Scripps Institution of Oceanography.


Fossil fuels, El Niño, and a touch of variability
The past month’s surge is not unexpected, but its strength is noteworthy. As fossil fuel burning pumps CO2 into the atmosphere, new highs in concentration have been achieved every spring at Mauna Loa since records began in 1958. The annual peaks and dips shown in the sawtoothed pattern in Figure 2 are a result of the seasonal cycle of vegetation growth in the Northern Hemisphere, which holds most of the world’s land areas. CO2 values normally top out in the second quarter of the year, as warming soils release CO2 but just before northern vegetation growth begins to take off. The global CO2 concentration then dips later in the year, as the increasingly lush summer vegetation absorbs huge amounts of CO2. These natural ups and downs occur on top of the inexorable year-by-year increase produced by human activity.

The tendency of a strong El Niño to foster drought and fire across much of the tropics cuts back on the ability of global vegetation to absorb CO2. This means that global CO2 levels tend to be higher during El Niño than they’d otherwise be (and lower during La Niña). The largest one-year jump in CO2 values in the Scripps data from Mauna Loa was the 3.7 ppm observed in 1998, at the tail end of our last “super” El Niño event.

Why such a spike this past month?
It’s not clear exactly what has led to such a big surge in CO2 concentrations at Mauna Loa during the past month. Industrial emissions don’t change quickly enough on a large enough scale to produce this big a spike. According to Keeling, “the levels last week were a bit higher, maybe by a part per million or two, than I would have projected even taking El Niño into account. I’m frankly not sure what is causing this, but I would not expect it reflects anything other than an unusual blob of air that temporarily settled over the central Pacific.”

A number of other sites around the globe also monitor CO2, with their measurements collated through a Global Greenhouse Gas Reference Network coordinated by NOAA. Readings from these sites can be several parts per million higher than those measured atop Mauna Loa, depending on local vegetation and circulation and each site’s proximity to major population centers. At the Harvard Forest site in central Massachusetts, daily CO2 concentrations have been hovering around 408-410 ppm over the last several weeks. This is “not particularly remarkable given the year and season,” said Harvard’s Steven Wofsy in an email.


Figure 3. Daily measurements of carbon dioxide collected atop Niwot Ridge, Colorado. The nighttime readings (red dots) typically run higher than daytime readings (green dots) due to the lack of photosynthesis at night. The Niwot Ridge values run slightly higher than the readings collected at the Mauna Loa site (dark line), which is located many hundreds of miles from any large land masses. Image credit: Courtesy Britton Stephens, NCAR.


Figure 4. Researchers work on a station near Niwot Ridge, Colorado, just west of Boulder, where carbon dioxide and other gases have been measured weekly for some 40 years. Image credit: UCAR/NCAR.


Another CO2 expert, Britton Stephens (National Center for Atmospheric Research), found little evidence of anything too dramatic in the last few weeks of data from a group of three dispersed stations in the U.S. West called Rocky RACCOON (Regional Atmospheric Continuous CO2 Network in the Rocky Mountains). “On that short time scale, nothing jumps out as unusual,” said Stephens. The CO2 values measured at several Colorado and Utah sites did show an uptick of several ppm from about April 14 to April 19, roughly a week after the highest values in Mauna Loa. According to Stephens, it’s possible that a large-scale “blob” of CO2 could have translated east from Hawaii to the central Rockies in that timespan.

The long-term outlook: unchanged
For those of us who have watched CO2 rise for years--the weekly values first passed 400 ppm in 2013--it is more than a bit unnerving to see daily and weekly numbers at Mauna Loa approaching the 410 ppm threshold. Some relief will come later this year, as the typical midyear dip begins. And the expected La Niña event may help tamp down the year-over-year increase in concentrations going into 2017.

Another bright spot: the Paris Agreement on Climate Change will become available for global leaders to sign on Friday (Earth Day). Leaders from 155 nations, including the U.S. and China, have signaled their intent to sign on the first day. That would be a record for any international agreement, and not a moment too soon. Major emission cuts in China may have already led to a decline in global emissions for 2015 (the data aren’t out yet), yet even the ambitious cuts in the voluntary national pledges of the Paris Agreement would not be enough in themselves to stave off the long-feared 2°C in global warming over pre-industrial levels.

That challenge comes into focus at the national level with the EPA’s 2014 inventory of U.S. emissions, released last week. It showed that total U.S. greenhouse emissions climbed 1.0% in 2014 following a 2.8% increase in 2013. Making matters worse, the EPA made a substantial upward revision to its estimates of U.S. methane emissions over the last few years, because research now shows that oil and gas operations were releasing significantly more methane than previously thought. Clearly, the substantial dip in U.S. emissions achieved during the late 2000s and early 2010s--variously attributed to high fuel prices, increased efficiency measures, and the transition from coal to natural gas--has ground to a halt. From this point on, each year in which U.S. emissions are climbing will make it that much harder for the nation to meet its Paris pledge: cutting U.S. emissions by 26-28% in 2025 compared to 2005 levels.


Figure 5. Probability of severe weather for Tuesday, April 26, 2016, as issued by NOAA/NWS Storm Prediction Center on Thursday, April 21. It's quite unusual to have probabilities as high as 30% outlined this far in advance of a severe weather threat. Image credit: NOAA/NWS/SPC.

Major severe weather threat taking shape for next week
We're monitoring the potential for one or more significant rounds of severe weather next week, most likely focused in southern Kansas, Oklahoma, and northern Texas. NOAA’s Storm Prediction Center (SPC) is already highlighting the risk of severe weather on Tuesday, Wednesday, and Thursday. The situation on Tuesday looks especially serious, as models are consistently agreeing that very rich low-level moisture and warm surface air will be juxtaposed with a powerful upper-level storm sweeping into the Great Plains from the Pacific. SPC began highlighting the risk of tornadoes on Tuesday in its Day 7 outlook issued on Wednesday--a very unusual step for SPC to take this far ahead of an event. The tornado threat is again mentioned in today’s Day 6 outlook, and the probabilities of severe weather have been raised (Figure 5], a sign of increasing forecaster confidence. Tuesday happens to be the 25th anniversary of the destructive central U.S. outbreak of April 26, 1991, which produced several violent tornadoes that killed at least 21 people, many of them residents of a devastated mobile home community in Andover, Kansas.

We’ll be back with an (upbeat!) Earth Day post on Friday.

Bob Henson


Climate Change El Niño

Warmest March in Global Recordkeeping; 2016 Roars Ahead of Pack

By: Jeff Masters and Bob Henson , 4:39 PM GMT on April 19, 2016

March 2016 was by far the planet's warmest March 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 Tuesday. In the NOAA database, March 2016 came in a full 1.22°C (2.20°F) warmer than the 20th-century average for March of 12.7°C (54.9°F), as well as 0.32°C (0.58°F) above the previous record for March, set in 2015. This is a huge margin for breaking a monthly global temperature record, as they are typically broken by just a few hundredths of a degree. The margin was just a shade larger than NOAA's previous record for any month of 1.21°C (2.18°F) above average, set in February 2016. NASA also reported the warmest March in its database, with the departure from average in its analysis slightly less than that for February (1.28°C vs. 1.34°C).

The past six months (as measured by departure from average in both the NOAA and NASA databases) all set records for their respective months as the warmest since 1880. 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 powerful 2015-16 El Niño event. This event peaked in December, but the warmest atmospheric readings (relative to average) usually lag the peak oceanic temperatures by a few months. NOAA’s global surface temperature for the year so far (January-March 2016) is an astounding 0.29°C (0.52°F) warmer than the previous record, set in 2015 (see Figure 2).
Figure 1. Departure of temperature from average for March 2016, the warmest March for the globe since record keeping began in 1880. Record warmth was observed over most land areas on Earth, with especially warm readings over much of Siberia, central Asia, northern Africa, the eastern U.S., western Canada, and Alaska. Image credit: National Centers for Environmental Information (NCEI).


Figure 2. Departure from average for the global January-through-March temperature for the years 1880 - 2016. This year has seen by far the warmest temperatures on record for each of the three months. Image credit: NOAA/National Centers for Environmental Information (NCEI).


March 2016 also marked the eleventh consecutive month that the monthly temperature record was broken and the sixteenth consecutive month (since December 2014) that the monthly global temperature ranked among the three warmest for its respective month in the NOAA database. Both global ocean and global land temperatures were the warmest on record for any March. Global satellite-measured temperatures in March 2016 for the lowest 8 km of the atmosphere were the warmest for any March in the 38-year record, and the third-largest warm departure from average any month, according to the University of Alabama Huntsville (UAH). This is the sixth consecutive month the UAH database has registered a record monthly high.

El Niño weakens to moderate strength
Strong El Niño conditions were observed during March in the equatorial Eastern Pacific, but El Niño is weakening quickly. The event peaked in strength in late November 2015, when the weekly sea surface temperatures (SSTs) in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W) peaked at a record 3.1°C above normal. By the week of April 6, 2016, the Niño3.4 SST anomaly had fallen to 1.3°C above average--just below the 1.5°C threshold between "strong" and "moderate”—and it remained at that level on April 13. Temperatures averaged through the upper 300 meters (1000 feet) of the tropical Pacific have already fallen below the seasonal norm, and NOAA expects a transition to neutral conditions during late Northern Hemisphere spring or early summer 2016, with a 65% chance of a transition to La Niña conditions by the August-September-October peak of the Atlantic hurricane season.



Figure 3. Arctic sea ice age for the week of March 4 - 10 from 1985 to 2016. The oldest ice--at least 5 years or older--is at its smallest level in the satellite record, representing only 3 percent of the total ice cover. Image Credit: NSIDC, courtesy University of Colorado Boulder, M. Tschudi, C. Fowler, J. Maslanik, R. Stewart, W. Meier.

Arctic sea ice falls to 2nd lowest March extent on record
Arctic sea ice extent during March 2016 was the second lowest in the 38-year satellite record, just above the record low set in March 2015, according to the National Snow and Ice Data Center (NSIDC). Arctic sea ice reached its annual maximum extent on March 24, 2016, and set a new record for the lowest maximum extent in the satellite record. The previous record was set just last year. However, there is little correlation between the maximum winter extent and the minimum summer extent observed in September. The key to getting a low summer ice extent is to get an earlier-than-average start to surface melting. This allows the snow to darken and expose the ice below earlier, which in turn increases the amount of solar heat absorbed, allowing more ice to melt.

Four billion-dollar weather disasters from late February through March 2016
According to the March 2016 Catastrophe Report from insurance broker Aon Benfield, three billion-dollar weather-related disasters hit the planet in March, and a third disaster from late February accumulated enough damage claims to be rated a billion-dollar disaster by the end of March. All of these disasters were severe weather outbreaks in the United States. From January - March 2016, there were seven billion-dollar weather disasters (this was updated to nine in the April Aon Benfield catastrophe report). This is well ahead of pace of five such disasters in January - March 2013--the year with the most billion-dollar weather disasters on record, with 41. Last year had only two billion-dollar weather disasters through March. Here is the tally of billion-dollar weather disasters so far in 2016:

1) Drought, Vietnam, 1/1 - 3/1, $6.7 billion, 0 killed
2) Winter Weather, Eastern U.S., 1/21 - 1/24, $2.0 billion, 58 killed
3) Winter Weather, East Asia, 1/20 - 1/26, $2.0 billion, 116 killed
4) Drought, Zimbabwe, 1/1 - 3/1, $1.6 billion, 0 killed
5) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 3/4 - 3/12, $1.25 billion, 6 killed
6) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 2/22 - 2/25, $1.2 billion, 10 killed
7) Severe Weather, U.S., 3/17 - 3/18, $1.0 billion, 0 killed

And here are the three disasters from late February through the end of March 2016:


Disaster 1. A powerful spring-like winter storm brought severe thunderstorms and heavy snowfall across much of the Central and Eastern U.S. from February 22 - 25, killing ten and injuring dozens more. The National Weather Service confirmed 59 tornado touchdowns, including four rated EF3. Total damage was estimated at $1.2 billion. In this image, we see damage in Waverly, Virginia a day after a tornado barreled through the small community on February 25, 2016. Tornadoes killed four people in Virginia on February 24. Image credit: Jay Paul/Getty Images.

Disaster 2. A record-strength upper-level low pressure system that stalled out over Northern Mexico and Southern Texas brought widespread severe weather and at least $1.25 billion in damage to the U.S. from March 4 - 12. In this photo, we see flood damage in Haughton, Louisiana, on March 9, 2016, after rainfall in excess of 20" in a four-day period hit the Shreveport area, bringing historic flooding. Image credit: Michael Dean Newman.


Disaster 3.  A stationary front draped over Texas and the Gulf Coast on March 17-18 triggered widespread severe weather. Large hail and damaging winds hit Texas, Mississippi, Arkansas, Louisiana and Florida. The greatest damage occurred in Dallas-Fort Worth, where tennis ball-sized hail pummeled southern Tarrant County. Parts of southern Mississippi recorded baseball-sized hail. Total economic losses were expected to be $1 billion. In this photo, we see menacing mammatus clouds over Boerne Stage Field, Texas, on March 18, 2016. Image credit: wunderphotographer agrant414.


Disaster 4. A strong storm system tracked across central and eastern sections of the United States from March 22 - 25, injuring several people. The storm brought tornadoes, large hail, damaging straight-line winds and heavy snow to portions of the Rockies, Plains, Midwest, and Southeast. The costliest damage resulted from hail and thunderstorm winds in Texas, Oklahoma, Louisiana, Arkansas, Mississippi, Alabama and Florida. Heavy snow and near hurricane-force winds caused property damage and travel delays throughout the Rockies and the High Plains. In this photo, we see an impressive shelf cloud from a thunderstorm over Tampa, Florida, on March 25, 2016. Image credit: wunderphotographer chelina.

Notable global heat and cold marks set for March 2016
Hottest temperature in the Northern Hemisphere: 45.0°C (113.0°F) at Bokoro, Chad, 1 March
Coldest temperature in the Northern Hemisphere: -54.0°C (-65.2°F) at Tsetsen Uul, Mongolia, 8 March
Hottest temperature in the Southern Hemisphere: 47.0°C (116.6°F) at Mardie, Australia, 3 March
Coldest temperature in the Southern Hemisphere: -72.8°C (-99.0°F) at Pole of  Inaccessibility, Antarctica, 27
March
(Courtesy of Maximiliano Herrera.)

Major weather stations that set (not tied) new all-time heat or cold records in March 2016
Ilorin (Nigeria) max. 40.2°C (104.4°F), 2 March
Tabligbo (Togo) max. 41.0°C [105.8°F), 2 March
Caracarai (Brazil) max. 39.6°C [103.3°F], 4 March

Kannur (India) max. 39.0°C, 8 March, followed by 39.1°C [102.4°F] on 11 March
La Macarena (Colombia) max. 39.4°C [102.9°F], 10 March
Cumaral (Colombia) max. 38.0°C [100.4°F], 10 March
Kozhikode (India) max. 38.1°C, 11 March, followed by 38.6°C [101.5°F] on 13 March
Pointe Canon (Rodrigues Island, Mauritius) max. 34.1°C [93.4°F], 18 March  
Attapeu (Laos) max. 41.5°C [106.7°F], 19 March
Dawei (Myanmar) max. 39.0°C [102.2°F], 20 March
Puerto Paez (Colombia) max. 40.4°C [104.7°F], 20 March
El Guamo (Colombia) max. 41.4°C [106.5°F], 23 March
Magangue (Colombia) max. 40.2°C [104.4°F], 23 March
Ahmednagar (India) max. 44.4°C [111.9°F],  23 March
Batu Embun (Malaysia) max. 38.5°C [101.3°F], 25 March
Hanimadhoo (Maldives) max. 34.5°C [94.1°F], 30 March
(Courtesy of Maximiliano Herrera.)

Four all-time national heat records and one all-time cold record set in Jan-Mar 2016
From January through March 2016, four nations or territories 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. Our data source is 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. 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.

April is off to a sizzling start
Widespread, intense heat has afflicted a huge swath of the tropics during the first half of April, from Central Africa to the Philippines. The heat wave across Southeast Asia has been particularly extreme--the worst there since at least 1960--with all-time records set at a number of locations. WU weather historian Chris Burt takes a closer look at the extraordinary heat of April, including two new all-time national records, in his Tuesday blog post. We'll have a complete list of all-time national records for this month in our April climate roundup, coming in mid-May.

Jeff Masters and Bob Henson


Climate Change Climate Summaries

Fantala Tied for Strongest on Record for Indian Ocean; Massive Flash Flood in Houston

By: Bob Henson , 8:47 PM GMT on April 18, 2016

Fierce Tropical Cyclone Fantala stormed to Category 5 strength north of Madagascar over the weekend with an impressive burst of strengthening, making the cyclone as strong as any on record anywhere in the Indian Ocean. Fantala’s estimated peak sustained winds of 150 knots (173 mph), averaged over 1 minute by the Joint Typhoon Warning Center, are tied with those of Tropical Cyclone Agnielle (November 1995 peak 1-minute winds of 150 knots) as the strongest in the Southwest Indian Ocean. Fantala and Agnielle both top the record holder for the North Indian Ocean (Super Cyclonic Storm Gonu, June 2007, peak 1-minute winds of 145 knots). Reliable satellite-based records for the Indian Ocean only go back to 1990, but Fantala’s power is still remarkable, and quite evident in satellite imagery. [Update: An earlier version of this post had stated that Fantala was unrivaled as the strongest in the Indian Ocean. Thanks to Phil Klotzbach, CSU, for bringing Cyclone Agnielle to our attention. Klotzbach also includes Tropical Cyclone Monica as an Indian Basin storm, based on its peak 1-minute winds of 155 knots occurring west of longitude 135°E. Definitions vary on the boundary of the Indian Ocean in this area. Monika reached peak strength north of Australia in the Arafura Sea, which is considered by several sources, including the CIA World Factbook, to be part of the western Pacific Ocean.]


Figure 1. A visible image of Tropical Cyclone Fantala collected at 1025Z (6:25 am EDT) on Monday, April 18, 2016, by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on board the Aqua satellite. The north tip of Madagascar can be seen at bottom. Image credit: NASA Goddard MODIS Rapid Response Team.


Figure 2. An enhanced infrared image of Tropical Cyclone Fantala collected at 1020Z (6:20 am EDT) on Monday, April 18, 2016, by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on board the Aqua satellite. Image credit: RAMMB/Colorado State University.

How Fantala got so strong, and what lies ahead
Conditions were highly favorable for Fantala to intensify. Wind shear has been fairly low over the storm for the last couple of days, around 10 knots, and sea surface temperatures along Fantala’s track have been around 29 - 30°C, plenty warm for tropical development and roughly 1 to 2°C above average (see Figure 3 below). On the other hand, the heat content of the upper ocean has not been particularly large over the last several days (see Figure 4), which implies that a storm as strong as Fantala could easily churn up cooler water. This makes it even more impressive that Fantala has managed to hang onto Category 4/5 strength for more than 48 hours, especially given its relatively slow motion.

After moving northwest for the last couple of days, Fantala is now crawling westward at about 4 knots as it embarks on a tight cyclonic loop that will turn its course around nearly 180 degrees to a southeast bearing. By late this week, Fantala may veer toward the southwest and could eventually approach Madagascar, though the JTWC projects it to be only a Category 1 or 2 cyclone by week’s end.


Figure 3. Departures from the seasonal norm (anomalies) in sea surface temperature across the globe, averaged for the period from March 13 to April 9, 2016. Image credit: NOAA/ESRL/PSD.


Figure 4. Oceanic heat content (OHC) in the upper part of the southwest Indian Ocean as of 06Z (2:00 am EDT) Monday, April 18, 2016. The forecast track of Fantala over the next 120 hours is outlined by hurricane symbols. Over the last several days, Fantala moved northwestward over an area of OHC of less than 35 kilojoules per square centimeter (the blue-green color on the map). Tropical cyclones are more likely to undergo rapid intensification when OHC is greater than 50 kilojoules per square cm. Fantala's initial strengthening from tropical storm to Cat 3 strength (Apr. 12 - 14] occurred around longitudes 65°E - 70°E, while Fantala was passing over heat content between 50 and 100 kilojoules per square cm. Image credit: RAMMB/Colorado State University.


A string of basin records for tropical cyclone strength
Many parts of the tropics have seen record-warm sea surface temperatures in 2015 and 2016, triggered by a strong El Niño on top of longer-term warming caused by human-produced greenhouse gases. These unusual readings have added fuel to the fire of tropical cyclone production. Along with Fantala’s record-setting performance in the Indian Ocean, two other ocean basins have seen their strongest cyclones on record in the past six months, as measured by 1-minute wind speeds confirmed in post-storm analyses. (Many agencies around the world calculate averages based on longer intervals, such as 10 minutes.)

Northeast Pacific: Hurricane Patricia, October 2015, 215 mph
Southwest Pacific: Tropical Cyclone Winston, February 2016, 180 mph



Figure 5. Residents of an apartment complex in the Greenspoint area of north Houston use an air mattress to evacuate their flooded homes on Monday, April 18, 2016. Image credit: AP Photo/David J. Phillip.

Houston walloped by massive flash flooding
At least two fatalities and more than 1200 high-water rescues were reported as the Houston area was socked on Monday morning by a huge mesoscale convective system (MCS) that drifted southeast across the area, dumping eye-popping amounts of rain: 6” - 8” over central Houston, with 12” - 18” common over the far western suburbs (see Figure 7). While individual thunderstorms often weaken after dark, the large mass of thunderstorms that makes up an MCS will often persist overnight and into the next morning, as the MCS cloud tops radiate heat to space and instability is enhanced. Countless roads and homes were flooded throughout the Houston area on Monday morning, and at one point power was out to more than 100,000 customers. City offices and mass transit lines were forced to close.


Figure 6. VIIRS infrared satellite imagery of the intense thunderstorms moving into the Houston area at 0835Z (3:35 am CDT) Monday, April 18, 2016. The Sabine River, separating Texas and Louisiana, can be seen in white against the east edge of the bright red, which denotes very cold cloud tops. Image credit: RAMMB/Colorado State University and Suomi NPP.


Figure 7. Rainfall amounts across Harris County, including the greater Houston area, for the 24 hours ending at 3:37 pm CDT on Monday, April 18, 2016. Image credit: Harris County Flood Control District.


The morning deluge drew some comparisons to Tropical Storm Allison, which devastated Houston as it lingered over Texas for several days in June 2001. Allison’s total rains were far heavier than today’s, topping 30” in places. However, today's flood was "flashier" than Allison, with extremely heavy rains over a short period. As noted by Capital Weather Gang, the 9.92" of rain at Houston Intercontinental Airport as of 3 pm CDT is the second heaviest calendar-day amount since airport record-keeping began in 1969, behind only the 10.34" recorded on June 26, 1989, during the city's "first" Tropical Storm Allison. It is also the second highest calendar-day total for any official Houston location going back to 1889, although it pales next to the nation's astounding 24-hour rainfall record of 43", recorded in Alvin, just south of Houston, on July 25, 1979.

Because the Houston area is so flat, water easily drains off paved areas and collects on the surface during high rainfall rates, so it doesn’t take an Allison-level event to produce widespread flooding. Houston’s west and northwest suburbs have experienced major growth over the last 10-20 years, which may be exacerbating the effect of a given rainstorm. As of midday Monday, the Buffalo Bayou in west Houston (Piney Point Village) was projected to crest at 61 feet, only about 3 inches short of its record 61.2-foot crest from March 4, 1992. However, as shown in Figure 7, it looks unlikely to hit that projection. Downtown, the Buffalo Bayou’s expected crest of 33.1 feet is far below the 42 feet observed in Allison and the 1935 record of 49 feet.

The complex of storms across Houston developed in weak upper-level flow near the edge of a sprawling upper-level low that brought 40” to 50” of snow across the foothills west of Denver, Colorado. At lower elevations, a foot or more of wet snow was recorded across large parts of the Front Range urban corridor. As expected, a rich stream of moist air from Texas to Nebraska led to streaks of very heavy rain throughout the Southern and Central Plains. Amounts over the weekend topped 7” west of Fort Worth, TX, and moderate to major river flooding is occurring over parts of southwest Oklahoma and northwest Texas. Amounts of 4” - 6” were common across southwest Nebraska.

We’ll be back on Tuesday with a new post.

Bob Henson


Figure 8. In west Houston (Piney Point Village), the Buffalo Bayou surged more than 28 feet in less than 18 hours. The floodwaters from Monday morning’s rain will fall short of reaching the 61-foot crest projected earlier Monday morning, although more rain is possible Monday night and later in the week. Image credit: NOAA/NWS Advanced Hydrologic Prediction Service


Figure 9. Kaicee Crowley walks through floodwaters to get belongings out of her stranded car at the North Main Street exit off I-45 in Houston on Monday, April 18, 2016, as White Oak Bayou comes over its banks and floods the freeway. Image credit: Karen Warren/Houston Chronicle via AP.





Hurricane Flood Extreme Weather

Bill Gray: A Towering Figure in Hurricane Science

By: Bob Henson and Jeff Masters , 7:46 PM GMT on April 17, 2016

Famed hurricane research William Gray passed away at his home in Fort Collins, CO, on Saturday, April 16, 2016. His death came just as colleagues were gathering in San Juan, Puerto Rico, for the American Meteorological Society’s 32nd Conference on Hurricanes and Tropical Meteorology, a meeting that Gray had attended regularly since the 1960s. Gray’s best-known research contribution was his founding of seasonal hurricane prediction techniques, which both emerged from and led to a growing understanding of how phenomena such as El Niño and La Niña influence the likelihood of tropical cyclones. Gray published many dozens of peer-reviewed papers, mainly in tropical meteorology. Late in his career, Gray spoke out passionately against the global consensus on climate change science, as noted in a memorial published by Colorado State University (CSU)--Gray’s professional home for more than 50 years.

Figure 1. Bill Gray. Image credit: CSU.

Drawn to hurricanes in the Windy City
As a youth in Washington, D.C., Gray aspired to become a pro baseball player. That career path was derailed by a knee injury while Gray was an undergraduate student at George Washington University. Shifting career paths and locations, Gray joined the U.S. Air Force in 1953 and spent a year studying meteorology at the University of Chicago--then one of the nation’s leading focal points for atmospheric science, a still-small but fast-growing field at the time.

After several years as an Air Force forecaster, Gray returned to Chicago, completing his master’s degree in meteorology in 1959 and his doctoral degree in geophysical sciences in 1964. Gray was introduced to tropical meteorology by his eventual advisor and mentor, Chicago professor Herbert Riehl. Gray completed his dissertation on internal stress characteristics and scales of motion within hurricanes. Data for that project came from reconnaissance flights into three 1958 hurricanes: Cleo, Daisy, and Helene. Gray himself participated in a flight into Helene.

Dr. Riehl left Chicago to found CSU’s Department of Atmospheric Science in 1960. Gray followed in 1961, remaining at CSU for his entire career. The two played a huge role in building CSU’s role--somewhat paradoxical for a campus near the Rocky Mountains--as a major center for tropical meteorology. Much like his Chicago colleague T. Theodore “Ted” Fujita (creator of the Fujita Tornado Damage Scale), Gray was first and foremost an observationalist who paid meticulous attention to data. While Fujita focused on processes within storms, Gray’s career eventually gravitated toward the larger-scale analysis of the regional and global environments that shaped hurricane activity. One of his primary insights was on the role of wind shear in controlling hurricane growth and decay. In his landmark 1968 paper “Global View of the Origins of Tropical Disturbances and Storms,” Gray published a detailed analysis of the globe’s favored regions for tropical cyclone activity, at a time when satellite imagery was in its infancy.


Figure 2. An analysis of origin points for tropical storms around the globe. Image credit: William M. Gray, “Global View of the Origins of Tropical Disturbances and Storms,” Monthly Weather Review 96, October 1968.

Developing the seasonal outlooks
It was the record-strong El Niño of 1982-83 that piqued Gray’s interest in seasonal hurricane prediction. Right from the start, the CSU forecasts were based on correlations among various factors found to be associated with Atlantic hurricane activity. Gray was the first to develop a formula that incorporated such processes into an estimate of how much activity an entire season might produce. Gray launched his technique by taking into account three factors: the quasi-biennial oscillation, the state of the El Niño-Southern Oscillation, and the departure from the seasonal average of sea level pressure across the Caribbean Sea. The technique gradually expanded to incorporate a wide array of other variables.

Gray’s first seasonal prediction--archived online, together with all subsequent outlooks--was published on May 24, 1984. “Until now,” he noted, “there has been no objective and skillful method for indicating whether a coming hurricane season was going to be an active one or not.” Perhaps sensing where the outlooks might lead, he added: “This paper has been prepared for the professional meteorologist, the news media, and any interested layman.” Gray issued forecasts each June and August from 1984 onward, adding April and December outlooks starting in 1995 and bringing in graduate student Phil Klotzbach in 2000. (Dr. Klotzbach became lead author of the outlooks starting in 2006.) The April 2016 outlook was released on April 14.

Despite occasional funding challenges, and questions about the value of seasonal outlooks that cannot pin down individual storms, the CSU outlooks have been a spectacular success in drawing media, public, and stakeholder attention to hurricane risk. They have also inspired more than a dozen other organizations--including NOAA--to issue similar outlooks. CSU’s June and August outlooks have demonstrated significant skill in predicting overall tropical cyclone activity in the Atlantic, as measured by a blend of six indices. Their April outlooks are less skillful, but in 23 out of 33 years they accurately pegged months ahead of time whether the coming season would see above- or below-average activity. One of Gray’s biggest forecast successes was predicting--as far back as 1990--the onset of a very active era of Atlantic hurricanes that began with a bang in 1995 and which may have now drawn to a close. Gray attributed the 1990s shift to a change in the Atlantic Thermohaline Circulation, a conclusion that remains somewhat controversial, although the shift itself is beyond dispute.

Much of the biographical material above was drawn from the excellent chapter-long portrait of Gray in Chris Mooney’s 2007 book “Storm World.”


Figure 3. Dr. Bill Gray at the podium of the American Meteorological Society’s 27th Conference on Tropical Meteorology, held in April 2006 in Monterey, California. Image credit: Jeff Masters.

Reflections from Dr. Jeff Masters on Bill Gray's career
I had the honor of chatting with Bill Gray a number of times at hurricane conferences, and enjoyed his colorful presentations and tremendous insight on how hurricanes work. His death is a tremendous loss for the hurricane research community, and I feel privileged to have known him. Dr. Gray's expertise was primarily data-based observational science and forecasts using statistical models. He was not a climate change specialist--though he did do some theoretical work related to climate change, attempting to link global temperature trends to the Atlantic Thermohaline Circulation. This work was not highly regarded in the scientific community. Dr. Gray did not accept any climate science done using complex computer-based General Circulation Models (GCMs). His belief that "the last century’s global warming of about 1 degree F is not a consequence of human activities" was prominently featured in the media and on the pages of many climate denier websites.

That aside, Dr. Gray's contributions to hurricane science deserve tremendous appreciation. In addition to his huge number of peer-reviewed scientific papers on hurricanes, he has given the hurricane science community perhaps an even greater gift: a plethora of his Ph.D. students have gone on to become formidable hurricane researchers in their own right. Dr. Gray mentored more than 70 master's and doctoral students at CSU. His final graduate student was Phil Klotzbach, who wrote a moving eulogy that highlighted Dr. Gray’s passion and dedication to atmospheric science:

“Even at the end, Dr. Gray was focused on his research. He gave me very clear instructions on various projects I should be conducting over the next few years. He was still sketching clouds using his legal pad and #2 pencils and discussing the intricacies of cumulus convection when I came to see him a few days before his death. He told me several times throughout my time at CSU: ‘The only immortality that you have as a professor is through your graduate students.’”

Bob Henson and Jeff Masters


Figure 4. Dr. William Gray (second from left) at his CSU office in October 2006 with Jonathan Vigh [left], a CSU student of Dr. Wayne Schubert and now at the National Center for Atmospheric Research, and (second from right) Phil Klotzbach (CSU). At far right is Brian McNoldy (University of Miami/RSMAS), who was a close colleague of Dr. Gray’s during his 14 years at CSU. Image credit: Courtesy Brian McNoldy.

Hurricane William Gray Tropical Meteorology

Central U.S. Dousing on Tap; Heavy Spring Snow in CO, WY

By: Bob Henson , 5:52 PM GMT on April 15, 2016

Soon to be abandoned by the jet stream, a strong upper-level low will park near the Four Corners this weekend, pulling in a rich moisture feed from Texas to Nebraska that will dump near-record April rain on the High Plains and tree-challenging wet snow along the Colorado/Wyoming Front Range. The upper low will be marooned for several days near Colorado, which will prolong the precipitation event and lead to some truly impressive totals.

As of midday Friday, winter storm warnings encompassed most of the Colorado high country as well as the urban corridor from near Colorado Springs, CO, to Cheyenne, WY. Snowfall totals predicted by the NWS through Sunday range from 8” - 14” in Denver and 6" - 12” in Cheyenne to a whopping two to four feet in the mountains and foothills just west of Denver, including areas within a few miles of Boulder. The biggest impact may be on local trees, many of which are now flowering and leafing out. The heavy, protracted snowfall is likely to break countless limbs and bring down many power lines. Streets and soil are quite warm around Denver after temperatures soared into the 70s on Thursday; between this and high-angle sunlight filtering through, there may be enough melting to keep snowfall on the ground and on highways well below the totals gleaned from snow measuring boards. Even so, a dense, slushy mess is like to impede travel thoughout the weekend.


Figure 1. WunderMap of projected flow at 300 mb (about 30,000 feet) from the 06Z Friday run of the GFS model, valid for 00Z Sunday (8:00 pm EDT) on April 17, 2016, shows the highly meridional (north-south) configuration of the jet stream, with the upper low near Four Corners largely cut off from the jet.


Figure 2. Precipitable water—the amount of moisture in the atmosphere available for producing rain or snow—will be at extremely high values for the location and season over the central High Plains by 18Z (2:00 pm EDT) Saturday, April 16, 2016. Areas of blue represent precipitable water 4 to 5 standard deviations above average. Also shown are surface highs and lows and winds at the 850-mb level, about a mile above sea level. This projection is from the 06Z Friday run of the GFS model. Image credit: Levi Cowan, tropicaltidbits.com.

An April snow to remember
Cut-off upper lows near the Four Corners are the most common set-up for heavy snow in the Denver area, especially in autumn and spring. The biggest snows in Boulder are several times more likely during El Niño than La Niña. However, a weak La Niña was in place 95 years ago this weekend, when a similar but stronger cut-off low led to the heaviest official 24-hour snowfall in U.S. records: 75.8”, recorded on April 14-15, 1921, at Silver Lake, about 30 miles west of Boulder at an elevation near 10,000 feet. The observer on site reported a total of 95 inches in just 48 hours, according to a Monthly Weather Review analysis cited in a Wasatch Weather Weenies blog post. (Another contender for top 24-hour snowfall is the 78” recorded at Mile 47 Camp, Alaska, on Feb. 7, 1963, according to WU weather historian Christopher Burt).


Figure 3. The snowstorm of March 17 - 19, 2003, was the most intense to strike the Denver area in over 80 years. In some parts of the Rocky Mountain foothills west of Boulder, more than 80 inches (two meters) of snow fell. This photo was taken near Nederland. Image credit: Carlye Calvin/ UCAR Image and Multimedia Gallery.

High Plains drencher
Not to be outdone by the Colorado snow, a strip from western Nebraska to northern Texas will see torrential rain over the weekend. The amount of precipitable water available for rain or snow will be close to record values for so early in the year across the central High Plains (above 1” at North Platte, NE, for example). The NOAA/NWS Weather Prediction Center is calling for widespread rains topping 4-5” by early next week from northern Nebraska to the Texas coast between Friday and Wednesday (see Figure 4). The projected maximum of about 7.5” close to North Platte would break the April precipitation record of 7.10” set in 1915. It would also be more than a third of the city’s typical yearly precipitation (20.19”).

While not as dramatic next to climatology, similar amounts could fall in localized areas toward western Oklahoma and northern Texas. Flood watches are in effect for parts of this area, but overall the moisture should be quite welcome. The CO/WY/NE area is already running well above average in precipitation for the year thus far; in contrast, much of the Southern Plains has seen less than half of its annual average to date (see Figure 5). This is part of a large dry swath--unusual for an El Niño spring--that extends westward all the way to southern California. As of Thursday, Los Angeles had seen less than half of its average precipitation for April (0.24”, vs. average of 0.51”) and little more than half for the water year since October 1 (5.80”, vs. average of 9.86”). Some parts of the area have done better, but overall the 2015-16 El Niño has been a major disappointment for the southern third of California.



Figure 4. Projected 5-day precipitation totals (rainfall and melted snow equivalent) from 12Z (8:00 am EDT) Friday, April 15, 2016, through Wednesday, April 20, 2016. Image credit: NOAA/NWS Weather Prediction Center.


Figure 5. Precipitation for 2016 through April 14 as a percentage of the annual average up to that point. Image credit: NOAA/NWS Advanced Hydrologic Prediction Service.

Severe weather threat over the Southern Plains this weekend
NOAA’s Storm Prediction Center has an enhanced-risk area extending across the central and southern High Plains on Friday, with a slight-risk zone over West Texas on Saturday and South Texas on Sunday. The bulk of the threat on Friday will be large hail, although tornadic storms may develop if the moisture surge from the south is especially robust. After a busy start to the 2016 tornado season in February and March, the pace has slackened in recent weeks, bringing the annual total closer to the long-term average (Figure 6).

Stay safe and have a great weekend, everyone!

Bob


Figure 6. Cumulative tornado counts for 2016 (black) against the distribution of high and low tornado counts for various other years. On each given day, the red curve represents the highest annual total up to that point in records going back to 1950, with the magenta curve showing the lowest total and the green curve showing the median value. The totals have been “inflation-adjusted” to remove the effects of increased tornado observing in recent decades. Image credit: NOAA/NWS Storm Prediction Center.

Winter Weather Extreme Weather Severe Weather

CSU Projects a Near-Average Atlantic Hurricane Season in 2016

By: Jeff Masters and Bob Henson , 4:00 PM GMT on April 14, 2016

The 2016 Atlantic hurricane season started off with a surprising bang in early January, when Hurricane Alex formed in the far Eastern Atlantic. However, a near-average Atlantic hurricane season is likely in 2016, said the hurricane forecasting team from Colorado State University (CSU) in their latest seasonal forecast issued April 14. Led by Dr. Phil Klotzbach, with special contributions from Dr. Bill Gray, the CSU team is calling for an Atlantic hurricane season with 13 named storms, 6 hurricanes, 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 93 (these numbers all take Alex into account.) The long-term averages for the period 1971 - 2010 were 12 named storms, 6.5 hurricanes, 2 intense hurricanes, and an ACE of 92. The CSU outlook also calls for a 50% chance of a major hurricane hitting the U.S. in 2016, with a 30% chance for the East Coast and Florida Peninsula and a 29% chance for the Gulf Coast. The Caribbean is forecast to have a 40% chance of seeing at least one major hurricane. All of these probabilities are very close to the long-term numbers from the last century.

Six years with similar pre-season February and March atmospheric and oceanic conditions were selected as “analog” years that the 2016 hurricane season may resemble:

1941 (6 named storms, 4 hurricanes, and 3 intense hurricanes)
1973 (8 named storms, 4 hurricanes, and 1 intense hurricane)
1983 (4 named storms, 3 hurricanes, and 1 intense hurricane)
1992 (7 named storms, 4 hurricanes, and 1 intense hurricane)
1998 (14 named storms, 10 hurricanes, and 3 intense hurricanes)
2003 (16 named storms, 7 hurricanes, and 3 intense hurricanes)

These six years all featured El Niño conditions transitioning to neutral or La Niña conditions. The average activity for these years was 9.2 named storms, 5.3 hurricanes, and 2 major hurricanes, all fairly close to the long-term average. However, as shown in the list above and in Figure 1 below, there is a great deal of variation among the six analog years chosen by CSU.


Figure 1. Two of the analog seasons cited in the new CSU hurricane outlook 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. The 1983 and 1998 seasons followed the two strongest El Niño events on record, which were roughly on par with the 2015-16 El Niño event.


Figure 2. Hurricane Alex approaching the Azores Islands in the far Eastern Atlantic on January 14, 2016. Alex peaked as a Category 1 storm with 85 mph winds on January 14, then weakened to a tropical storm with 70 mph winds when it made landfall on Terceira Island in the Azores on January 15. The storm caused minimal damage and was responsible for one indirect death. Alex was the first Atlantic hurricane in January since Alice in 1955, and the first to form in January since 1938. Image credit: NASA.

A boost from El Niño’s departure
The CSU team cited two main reasons why this may be an average hurricane season:

1) The El Niño event now fading in the eastern tropical Pacific is expected to transition toward neutral conditions this summer and either neutral or La Niña conditions by autumn (see the discussion below). If La Niña conditions are present this fall, this would tend to favor a busier-than-usual Atlantic hurricane season due to a reduction in the upper-level winds over the tropical Atlantic that can tear storms apart. Sea surface temperatures were 1.3°C above average over the past week in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for a weak El Niño event to be declared. By August-October, most dynamical models are calling for either cool-neutral conditions (Niño3.4 anomalies between 0 and -0.5°C) or La Niña conditions (Niño3.4 anomalies of -0.5°C or greater). The European Centre for Medium-Range Weather Forecasts (ECMWF) shows the best prediction skill of the various El Niño/Southern Oscillation (ENSO) models, and the average of the various ECMWF ensemble members is calling for a Nino 3.4 SST anomaly of approximately -0.4°C, just short of weak La Niña conditions. Several other models, including the NOAA Climate Forecast System (CFSv2), are projecting somewhat stronger La Niña conditions by the August-October period. In its monthly ENSO Diagnostic Discussion released on Thursday, NOAA's Climate Prediction Center issued a La Niña Watch, with the new CPC/IRI probabilistic outlook calling for a 65% chance of La Niña during the August-October period.

2) A fairly unusual pattern in sea surface temperature (SST) is present across the North Atlantic, leading to some uncertainty about how this factor will evolve later in the year. SSTs are now above average in the Northwest Atlantic and well below average in the far North Atlantic, a pattern that the CSU group has associated with the negative phase of the Atlantic Multidecadal Oscillation. Typically this pattern also leads to colder-than-normal water in the tropical Atlantic. However, SSTs in the Main Development Region (MDR) for hurricanes, from the Caribbean to the coast of Africa between 10°N and 20°N, were near to slightly above average in March 2016, with the exception of cooler-than-average waters just off the coast of Africa. SSTs have cooled across both the tropical and far northern Atlantic since late October, largely due to a persistent positive phase of the North Atlantic Oscillation (NAO) since November 2014. A positive phase of the NAO is associated with a strengthened Bermuda-Azores High and faster trade winds across the tropical Atlantic. The faster winds increase mixing of cool water to the surface. These cooler SSTs are associated with higher-than-normal sea level pressures, which can create a self-enhancing feedback that relates to higher pressure, stronger trades and cooler SSTs during the hurricane season. Virtually all African tropical waves originate in the MDR, and these tropical waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely. The April outlook concludes: “There are some hints of [cold water] emerging in the tropical Atlantic, but it remains to be seen if these cold anomalies will push further across the tropical Atlantic.”

As always, the CSU team included this standard disclaimer:

"Coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them. They should prepare the same for every season, regardless of how much activity is predicted."


Figure 3. Departure of sea surface temperature (SST) from average for March 2016, as computed by NOAA/ESRL. SSTs in the hurricane Main Development Region (MDR) between Africa and Central America (red box) were near average in the eastern Atlantic, and slightly above average in the Caribbean. Image credit: NOAA/ESRL.

How good are the April forecasts?
April forecasts of hurricane season activity are low-skill, since they must deal with the so-called "predictability barrier." April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season (although there is a fairly strong model consensus this year on a transition from El Niño toward La Niña). For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due on June 1, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years. NOAA issues its first seasonal hurricane forecast for 2016 in late May.

TSR predicts a below-average Atlantic hurricane season
The April 5 forecast for the 2016 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for a below-average Atlantic hurricane season about 20% below the long-term (1950-2015) norm and about 15% below the recent 2006-2015 ten-year norm. TSR is predicting 12 named storms, 6 hurricanes, 2 intense hurricanes and an Accumulated Cyclone Energy (ACE) of 80 for the period May though December. The long-term averages for the past 65 years are 11 named storms, 6 hurricanes, 3 intense hurricanes and an ACE of 101. TSR rates their skill level as low for these April forecasts--just 9 - 15% higher than a "no-skill" forecast made using climatology. TSR predicts a 29% chance that U.S. landfalling activity will be above average, a 27% chance it will be near average, and a 44% chance it will be below average. They project that two named storms will hit the U.S., with one of these being a hurricane. The averages from the 1950-2015 climatology are three named storms and one hurricane. They rate their skill at making these April forecasts for U.S. landfalls just 3 - 7% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects one named storm and no hurricanes. Climatology is one named storm and less than 0.5 hurricanes.

TSR’s two predictors for their statistical model are the forecast July - September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August - September sea surface temperatures (SSTs) in the tropical North Atlantic. Their model is calling SSTs 0.03°C below average and trade winds 0.15 m/s faster than average during these periods. Both of these factors should act to decrease hurricane and tropical storm activity. The July-September 2016 trade wind prediction is based on an expectation of near-neutral El Niño ENSO conditions in August-September 2016. They add: "Should the TSR forecast for 2016 verify it would mean that the ACE index total for 2013-2016 was easily the lowest 4-year total since 1991-1994 and it would imply that the active phase of Atlantic hurricane activity which began in 1995 has likely ended. However, it should be stressed that the precision of hurricane outlooks issued in April is low and that large uncertainties remain for the 2016 hurricane season." One factor to keep in mind: TSU’s outlook drew in part on NOAA CFSv2 model projections that conflicted with other major models in calling for El Niño to continue this autumn. NOAA has now corrected an initialization error in the CFSv2, and this month the model has made a major switch, now consistently pointing toward La Niña. CSU was able to this switch into account in developing its April outlook. The next TSR forecast will be issued on May 27.


Figure 4. The departure of tropical cyclone activity from average for the five years 2013, 1988, 1973, 1970, and 1954 (tropical cyclones include all tropical depressions, tropical storms, and hurricanes). These five years had ocean temperatures in the Western Hemisphere similar to what is predicted in the summer of 2016 by NOAA's North American Multi-Model Ensemble. During these five analog years, above-average activity was observed in the western Gulf of Mexico, along the U.S. East Coast, and along the Pacific coast of Mexico. Image credit: WU member Levi Cowan (tropicaltidbits.com)

Analog years from Levi Cowan
WU member Levi Cowan (tropicaltidbits.com) has come up with his own list of analog years for Atlantic and Eastern Pacific hurricane activity, based on the predicted pattern of ocean temperatures this summer from NOAA's North American Multi-Model Ensemble (NMME): 2013 (which featured 14 named storms, 2 hurricanes, and 0 intense hurricanes); 1988 (12 named storms, 5 hurricanes, and 3 intense hurricanes); 1973 (8 named storms, 4 hurricanes, and 1 intense hurricane) ; 1970 (10 named storms, 5 hurricanes, and 2 intense hurricanes); and 1954 (16 named storms, 7 hurricanes, and 3 intense hurricanes). Above-average activity was observed in the western Gulf of Mexico, along the U.S. East Coast, and along the Pacific coast of Mexico during these five years. The average activity for these years was 12 named storms, 4.6 hurricanes, and 1.8 major hurricanes.

We’ll have a post by Friday afternoon looking ahead to the major spring storm that's likely to bring severe weather and excessive rain this weekend to parts of the Southern and Central Plains and heavy snow to the Central Rockies.

Jeff Masters and Bob Henson

Hurricane

NWS LOWERS ITS VOICE: All-Caps Phaseout Starts in May

By: Jeff Masters and Bob Henson , 8:59 PM GMT on April 12, 2016

NOAA’s two operational supercomputers for weather prediction can carry out 5,000 trillion calculations per second. Until now, though, forecasters at the National Weather Service (NWS) could use only a measly set of 30 characters to translate that prodigous model output into the worded watches, warnings, advisories, and discussions that millions consult each day. A new era of commas, colons, parentheses, and lower-case letters--and maybe even the occasional question mark?--starts in May, when local NWS offices begin converting to mixed-case products. As NOAA put it in a news release on Monday: “LISTEN UP! BEGINNING ON MAY 11, NOAA’S NATIONAL WEATHER SERVICE FORECASTS WILL STOP YELLING AT YOU.”


Figure 1. A NOAA montage illustrates the evolution of communication technology at the National Weather Service.


As a 24/7 operational agency, the NWS is by nature cautious and deliberate when making changes that could affect how its work is disseminated in life-or-death situations. The agency’s shift to mixed case has been even more gradual than one might expect, mainly to ensure that its variegated user base can deal with the newly introduced character set. Many users (including WU--see below) feed NWS products into a wide variety of software.

Testing of the mixed-case format has been unfolding for most of this decade. At the National Hurricane Center, tropical weather outlooks and tropical cyclone discussions have been issued in mixed case beginning with the 2014 season. Four local NWS offices--Kansas City, MO; Louisville, KY; Spokane, WA; and Tallahassee, FL--have served as experimental testbeds since August 2011 for three mixed-case products: area forecast discussions, public information statements, and regional weather summaries. The national changeover in May involves all local offices switching to mixed case for these three products, with watches and warnings going mixed-case by August and most other NWS products by the end of the year.


Figure 2. Staff at the U.S. Weather Bureau office in Washington, D.C., prepare a forecast in July 1943, using data received by teletype from across the nation and plotted on maps. Image credit: Photo by Esther Bubley/Library of Congress, via Circuitous Root.


Figure 3. A Teletype Model 33 with paper tape reader and punch, on display at the National Museum of Computing. Many thousands of these models were sold in the 1960s and 1970s. Image credit: AlisonW/Wikimedia Commons.


A relic goes on the shelf
The practice of using a limited character set for NWS bulletins is a byproduct of the telegraph era. Telegrams were in all caps from the very first telegraph message ("WHAT HATH GOD WROUGHT", 1844]. As far back as the mid-1800s, telegraph machines were able to convert typed messages into Morse code and vice versa. By the early 1900s, these had evolved into hybrid printer/typewriter units called teleprinters. The most successful producer of these was a company founded in 1906 and renamed the Teletype Corporation in 1928, shortly before it was acquired by AT&T. Teletype machines were the standard mode of transmitting weather data when meteorology went through its enormous growth phase during and after World War II. They remained in common use as late as the 1980s, until personal computers became widespread.

The all-caps format of NWS bulletins emerged from the limits of the teletype keyboard, together with standards set by the World Meteorological Organization designed to accommodate nations with widely varying technological capabilities. No capital letters were allowed, and the only punctuation permitted was periods (.), ellipses (…), forward slashes (/), dashes (—), and pluses (+). These conventions went largely unseen by the public until the NWS website was established in the 1990s. Before that point, NWS text products were reformatted by newspapers or read aloud on TV and radio, including NOAA Weather Radio.

Forecasters found many ways to be creative within the old all-caps format, especially in forecast discussions that were originally designed for internal consumption and then opened to the public during the Internet era. You can find a rich set of classics archived in the Forecast Discussion Hall of Fame, including the best all-caps example of “talking like a pirate” you’re likely to encounter on land or sea.


Figure 4. The wide world of 95 characters now available to NWS forecasters to include as part of mixed-case messages.


From the front lines of mixed case
I asked Parks Camp, science and operations officer (SOO) at NWS/Tallahassee, about his office’s experience as a mixed-case testbed. “We received very little feedback one way or the other when we switched to mixed case,” Camp said. “Probably the biggest adjustment was internal. For example, with the area forecast discussion, forecasters have had to adjust how they write, taking advantage of the full suite of punctuation (not just periods and ellipses). When you spend most of your career writing in a particular style, it can take a little time to make the adjustment.”

Ron Miller, the SOO in Spokane, also chimed in: “Going with mixed case took a little getting used to, for both the meteorologists (who weren't used to typing mixed-case products) and the users,” he told me. One radio station commented that the mixed-case bulletins were harder to read and that the upper-case format was standard in the media world. However, says Miller, “In our digital world, upper-case is shouting. As such, many of the NWS upper-case products didn't sit well with web-savvy folks who saw this as poor etiquette. So it was nice to adhere to the societal norm.”

NWS meteorologist Art Thomas, who has been overseeing the national mixed-case changeover, said that about 20 out of 325 comments in a user survey advocated against making the change. “They fell into two broad categories: those that felt it was just easier to read upper case products (matter of personal preference) and those who felt upper-case letters added importance to our products.” Using all-caps will remain an option when forecasters truly want or need to emphasize something, said Thomas.

Jeff Masters on the Weather Underground solution: using hashtables to convert to mixed case
Back in 1998, two of Weather Underground's co-founders, Chris Schwerzler and Alan Steremberg, got tired of seeing the ALL CAPITAL LETTER ADVISORIES OF THE NATIONAL WEATHER SERVICE and decided to implement a clever programming trick to convert the files to mixed upper and lower case. Their solution: put every possible place name that could appear in the advisories into a giant 5 MB hash table, then write software that would search the hash table to recapitalize the text. They got their hands on a geographical database for the U.S. that had the names of every city and geographical feature, and used that as the starting point. For example, here are the entries in the hash table for everything Ann Arbor-related:

Ann Arbor
Ann Arbor Gulch
Ann Arbor Municipal Airport
Ann Arbor Township

It was then a matter of adding a few more items that needed recapitalization, like the rotating list of all hurricane names in the Atlantic. When a storm got its name retired, I would have to add all the potential variants of the new storm name to the hash table; when the hurricane season of 2005 rolled around, and we got into the Greek alphabet, I had to add a whole slew of new entries, like this:

Tropical Storm Alpha
Tropical Depression Alpha
Hurricane Alpha
Alpha
Alpha's

As the years went by, I noted over 1500 phrases that were not being recapitalized properly, and edited the hash table to add/delete these items. There were a few things that could never be properly handled this way: for example, the word "Orange" should be capitalized when it refers to Orange County, but not when it refers to the color orange. Likewise, the abbreviation for Sunday (Sun) should not be capitalized when it refers to our faithful star, the sun. It will be nice to have things in mixed case from the source, instead of trying to do the job ourselves!

Jeff Masters (WU perspective) and Bob Henson

Communication

New Re-Analysis Sheds Lights on the Mysteries of Hurricane Camille

By: Jeff Masters , 1:45 PM GMT on April 11, 2016

On the night of August 17, 1969, mighty Category 5 Hurricane Camille smashed into the Mississippi coast with incredible fury, bringing the largest U.S. storm surge on record--an astonishing 24.6 feet in Pass Christian, Mississippi (a record since surpassed by Hurricane Katrina's unimaginable 27.8' storm surge in Pass Christian in 2005.) Camille barreled up the East Coast and dumped prodigious rains of 12 - 20 inches with isolated amounts up to 31" over Virginia and West Virginia, with most of the rain falling in just 3 - 5 hours. The resulting catastrophic flash flooding killed 113 people, bringing Camille's total death toll to 256, making it the 15th deadliest hurricane in U.S. history. But just how strong was Camille at landfall? In NHC's original historical database, Camille was assumed to have become a Category 5 storm in the southern Gulf of Mexico, with steadily intensification occurring during the final 24 hours before landfall. This database had Camille making landfall with 190 mph winds, tying the storm with Super Typhoon Haiyan (in 2013 in the Philippines) for the strongest winds at landfall of any tropical cyclone in recorded history. However, Camille's landfall intensity was based on visual observations of the sea state from a hurricane hunter aircraft--a technique that is very inexact. Furthermore, comparison with other Category 5 hurricanes called into question Camille's assumed intensity during this final 24-hour period. So, just how strong was Camille?


Figure 1. Hurricane Camille as seen on Sunday, August 17, 1969, about eight hours before making landfall on the Mississippi coast. At the time, Camille was a peak-strength Category 5 storm with 175 mph winds. Image credit: NOAA/NCDC.

Thanks to a reanalysis effort by Margie Kieper of Florida International University and Chris Landsea and Jack Beven of NHC, published last week in the Bulletin of the American Meteorological Society, Camille has now been officially downgraded to 175 mph winds at landfall. The re-analysis puts Camille in second place for the strongest landfalling hurricane in U.S. history, behind the Great 1935 Labor Day Hurricane that hit the Florida Keys, which reanalysis showed had 185 mph winds and a central pressure of 892 mb at landfall. (The only other Category 5 hurricanes on record to hit the U.S. were 1992's Hurricane Andrew--165 mph winds and a 922 mb central pressure--and the 1928 “San Felipe” Hurricane in Puerto Rico--160 mph winds, 931 mb central pressure.) Category 5 hurricanes have maximum sustained winds of 157 mph or greater.


Figure 2. Ships beached by Hurricane Camille's record storm surge in Mississippi. Image credit: NOAA photo library.


Figure 3. The most intense world tropical cyclones at landfall, using the advisories taken from the National Hurricane Center in the Atlantic and Eastern Pacific, and the Joint Typhoon Warning Center (JTWC) for the rest of the world's oceans. Both agencies use 1-minute averaging times for their advisories, as opposed to the 10-minute averaging time used to report wind speeds by most international weather agencies and at most international airports. Note that Super Typhoon Haiyan was originally assessed to have 195 mph winds at landfall by JTWC, but these were reduced to 190 mph after a post-season reanalysis. Also, Hurricane Camille's winds at landfall have also been reduced in a recent reanalysis, from 190 mph to 175 mph.

Revised understanding of a superstorm
The track of Camille had only minor changes due to the re-analysis; the big changes were all to the storm's intensity. Revisions to Camille were accomplished by obtaining the original observations from ships, weather stations, coastal radars, Navy/Air Force/Environmental Science Services Administration (ESSA, now called NOAA) Hurricane Hunter aircraft reconnaissance planes, satellite imagery, and by analyzing Camille based upon our understanding of hurricanes today. The satellite imagery of 1969 was only marginally of use for knowing Camille’s exact position and intensity, because of poor navigation, coarse resolution, and spotty temporal coverage.

Camille is now thought to have reached its peak intensity of 150 knots (175 mph) shortly after a three-day period of steady intensification as the storm moved through the Western Caribbean, crossed the western tip of Cuba, then moved northwards to a position due west of Key West, Florida. As the storm closed in on the Mississippi coast, it is now realized that Camille underwent an eyewall replacement cycle (ERC)--a common occurrence in intense hurricanes whereby the eye of the storm contracts and grows unstable and collapses. The importance of the ERC—the cycle of temporary weakening followed by reintensification as the ERC completes and the new outer eyewall contracts—was not fully understood back in 1969, and would not be until a 1982 paper by Willoughby et al. Camille could no longer support its tiny 11-mile diameter eye when the storm was over the central Gulf of Mexico, and a concentric larger-diameter eye formed around the inner eyewall, resulting in a weakening of the hurricane to a high-end Category 4 storm with 135 knot (155 mph) winds. A hurricane hunter flight during this period reported a clear area that was possibly a moat that separated the inner and outer eyewalls: "Just as we were near the [eye] wall cloud we suddenly broke into a clear area and could see the sea surface below," the copilot, Robert Lee Clark, wrote in 1982. The concentric eyewall structure was also clearly seen on radar images.


Figure 4. WSR-57 radar image of Hurricane Camille from New Orleans at 1732 UTC 17 August 1969. Concentric eyewalls are seen, indicating an eyewall replacement cycle was underway. Check out this impressive 78-frame radar animation of Hurricane Camille's landfall the authors put together as part of the Supplementary Materials for the article. This is probably the earliest radar animation of a hurricane ever constructed.

As Camille approached landfall in Mississippi, the storm apparently was able to recover from the completion of the eyewall replacement cycle, taking advantage of light wind shear and very warm waters to re-intensify to a Category 5 storm with 150 knot (175 mph) winds in the 12 hours before landfall. These winds were concentrated over a small area, about 15 - 20 miles in diameter. According to the paper, "A pressure of 909 mb was measured by Mr. Charles Breath at the onset of the eye in his home just west of the bridge in Bay St. Louis, Mississippi, which was about 3 - 4 miles east of the landfall point. This marine aneroid barometer was subsequently tested and determined to be accurately calibrated. The 909-mb value had been the accepted central pressure value at landfall….However, Mr. Breath also measured a 904-mb pressure at a later point in the eye passage a short distance west of the first measurement….Given that the 904-mb pressure reading was taken near the eastern edge of the eye, a 900-mb central pressure is analyzed at landfall." In an email, lead author Margie Kieper told me: "In providing portions of the interview with Charles Breath Jr, I particularly wanted to show his understanding of barometric pressure, how it related to the intensity of the storm, how important it was to keep the barometer calibrated, and his reaction upon seeing it drop dramatically when Camille's eye approached.  I wanted to show the authenticity that gave to the readings--how similar his understanding was to that of a meteorologist."


Figure 5. The Breath home in in Bay St. Louis, Mississippi three days after Camille, August 20, 1969. Camille's lowest landfall pressure of 904 mb was measured by Mr. Charles Breath at this home. Workers are seen moving surge debris and replacing the roof--minus the Queen Anne dormer that was blown off. Photo courtesy of the Hancock County Historical Society, Bay Saint Louis, MS and the Bulletin of the American Meteorological Society.

Camille a rare hurricane that intensified up until a Gulf Coast landfall
While the re-analysis showed that Camille was not as strong at landfall as originally thought, it did strengthen from a Category 4 storm with 155 mph winds to a Category 5 storm with 175 mph winds in the twelve hours before landfall. This behavior contrasts with many other major hurricanes that have made landfall along the northern Gulf Coast, which weakened prior to landfall. The paper notes that "All 11 hurricanes—most notably Hurricane Katrina in 2005—during the period from 1985 to 2005 having a central pressure less than 973 mb 12 h before landfall in the northern Gulf of Mexico weakened during these last 12 h (Rappaport et al. 2010)." While the paper does not go into the reasons why Camille showed this unique behavior, I speculate that it was because of the storm's relatively small size, which meant that the storm was not able to suck in a large amount of air pollution particles from the Gulf Coast prior to landfall. Hurricanes that approach land are prone to weakening if they pull in large amounts of air pollution particles, which invigorate thunderstorms in the outer spiral bands, causing heavy rain that drags down cold air from aloft to the surface, creating pools of cold air near the surface that act to block the inflow of warm, moist air into the hurricane's core, thus weakening the storm. A 2015 post of mine, Air Pollution and Dust Credited With Weakening Hurricanes Irene and Katrina, describes the process in more detail.

Kudos to Margie Kieper
The first author of the paper, Margie Kieper, is a name long-time readers of this blog will recognize. Margie got her start in hurricane science thanks to this blog and Hurricane Katrina, whose storm surge she analyzed in a series of articles that appear in our storm surge pages. At my encouragement, Margie gave up her career in database management and enrolled in Ph.D. school in Tropical Meteorology at Florida International University three years ago. She has completed her prelims, and is working on her thesis project. The Hurricane Camille re-analysis paper showcases her thorough research methodology--Margie found a large amount of data on Camille that had previously been unknown, and doggedly slogged though the material to come up with what should be the authoritative final scientific analysis of the storm's track and intensity.

Jeff Masters

Hurricane

The North Atlantic Blob: A Marine Cold Wave That Won’t Go Away

By: Bob Henson , 6:01 PM GMT on April 08, 2016

When you look at a map of global surface temperatures for 2015, the first impression you might get is a planet with a bad sunburn. Almost every part of the globe saw above-average temperatures during Earth’s warmest year on record, and there was unprecedented warmth across many parts of the tropical and subtropical oceans (Figure 1). The next thing you’d probably notice is a blue blob in the North Atlantic, sticking out like a frostbitten thumb. No one knows exactly why, but this blob of unusually chilly water, roughly half the size of the United States, has taken up what seems like semi-permanent residence in the North Atlantic Ocean.

It’s normal for ocean temperatures to wax and wane on all kinds of time scales. What’s more uncommon is for a cold anomaly this large and strong to persist for so long, especially when the rest of the planet is trending ever warmer.


Figure 1. Surface temperatures for 2015 were at record cold values for part of the far North Atlantic, even as most of the globe was unusually warm. Image credit: NOAA/NCEI.


Heat waves and cold waves at sea
The North Atlantic’s cold blob once had a hot-headed cousin. Thousands of miles away, on the other side of North America, a zone of above-average sea surface temperatures (SSTs) in the northeast Pacific gained fame as “The Blob.” While it was in place, from about 2013 through most of 2015, The Blob was closely linked with intense upper-level ridging over and near it. The Pacific jet stream arced northward, away from California, which helped strengthen the fierce multiyear drought still plaguing much of the state. Once it became clear last autumn that a strong El Niño was on its way, experts predicted that a juiced-up storm track in the Northeast Pacific would churn up the waters enough to dilute and vanquish The Blob. Sure enough, The Blob eroded to near-nothingness in just a few weeks during late 2015, and the West Coast from San Francisco northward got drenched by wet Pacific storms throughout the subsequent winter.

One way to think of The Blob is as a “marine heat wave,” according to Hillary Scannell. Now a graduate student at the University of Washington, Scannell analyzed the full spectrum of these oceanic warm spots in a Geophysical Research Letters paper, written with colleagues at the University of Maine, NOAA, and the Gulf of Maine Research Institute and published in March. Scannell is also coauthor on a new Progress in Oceanography paper, led by Alistair Hobday (CSIRO), that lays out suggested metrics for defining marine heatwaves. Such events can have big impacts on ocean ecology: marine heatwaves have been implicated in hundreds of years of coral-reef damage, and record-warm ocean temperatures have caused extensive damage this year to the Great Barrier Reef.


Figure 2. 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 globalcoralbleaching.org.


Just like atmospheric heat waves, oceanic heat waves come in all sizes and shapes, typically defined by SST anomalies (departures from the seasonal average). But while a heat wave over land is ultimately doomed by the arrival of autumn, marine heat waves can recur for two or more years, because of what’s known as the reemergence mechanism: warm anomalies that stay just below the surface during the placid flow of summer can return to the surface in winter by the deeper mixing brought about by strong storms. As one might expect, large, long-lived oceanic heat waves lasting a year or more are less common than briefer ones.

Using this analogy, we might picture the North Atlantic’s blob as a “marine cold wave.” Although such cold waves weren’t addressed in the GRL paper, Scannell has analyzed them. As with marine warm waves, she told me that brief, smaller, and/or weaker marine cold waves are more common than large, long-lived, stronger ones.

Once a marine heat wave or cold wave takes shape, its blob of above- or below-normal SSTs may feed back into the atmosphere, helping to intensify and reinforce the circulation patterns that brought it to life. There is one important distinction: cold surface blobs are easier than warm blobs to disrupt. This is because the ocean is more likely to mix (convect) when colder water sits astride warmer water, just as the atmosphere is more prone to intense storminess when cold upper level air moves atop warm, moist surface air. When you consider this instability, it’s even more impressive that the North Atlantic’s cold blob has outlived the Northeast Pacific’s warm blob.

“The persistence--the staying power--of this anomaly is really pretty remarkable,” noted Michael Mann (Pennsylvania State University) in an email. “It is particularly striking that during the warmest year on record globally [2015], this region saw its coldest year on record.”

Putting the brakes on Atlantic circulation
Might the cold blob be a sign of something else going on--in particular, a long-term slowdown in the Atlantic Meridional Overturning Circulation? The AMOC transports heat northward through the North Atlantic, via the Gulf Stream and related currents. Completing the loop, dense surface water--generated near the surface in the frigid Labrador Sea, southwest of Greenland--sinks and flows southward.


Figure 3. A schematic of the Atlantic ocean circulation, with surface currents in red, deep currents in blue, and winter sea-ice cover in white. NADW denotes North Atlantic Deep Water. Image credit: Stefan Rahmstorf, “Risk of sea-change in the Atlantic,” Nature 1997.


Scientists have warned for years that the AMOC is likely to slow down in the coming decades due to human-induced climate change. Estimates in the latest IPCC assessment (2013) range from an 11% to 34% slowdown during this century, depending on the pace of global greenhouse emissions. A warming planet would produce this slowdown in several ways, such as increased melting from the Greenland Ice Sheet or increased export of sea ice out of the Arctic Ocean. Either or both of these mechanisms could send additional fresh (non-salty) water around southern Greenland and into the Labrador Sea. Because fresh water is less dense than salty water, this could inhibit the formation of bottom water and slow down the AMOC. (Fortunately, atmospheric warming should more than offset AMOC-related cooling, even on a regional basis, so the shift this century is not expected to bury New York in mountains of snow as depicted in the 2004 film “The Day After Tomorrow.”)

A number of leading scientists believe that meltwater from Greenland has already produced an AMOC slowdown. Mihai Dima and Gerrit Lohmann (Alfred Wegener Institute for Polar and Marine Research) argued in a 2010 paper that the global conveyor belt has been weakening since the 1930s, with a dramatic shift around 1970. In a 2015 Nature Climate Change paper, Stefan Rahmstorf (Potsdam Institute for Climate Impact Research) and colleagues, including Mann, made this case by using 1000 years of paleoclimate proxy data. They estimate that the AMOC actually began slowing in the 20th century--and especially since the 1970s, when the slowing has no precedent in their millennial-scale analysis. “Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC,” they warned. The paper also presents NASA data for the 20th century that show a cold trend in SSTs in roughly the same location as the current North Atlantic cold blob. In a 2015 RealClimate article, Rahmstorf noted that the location of the current cold wave “happens to be just that area for which climate models predict a cooling when the Gulf Stream System weakens.” 

To gauge the strength of the AMOC more directly, a project called RAPID has been using an array of buoys and other instruments straddling the subtropical northwest Atlantic for the last decade-plus. “RAPID does show a declining decadal trend in the AMOC since 2004, which is consistent with our data,” Rahmstorf said in an email. More data will soon arrive from a new project called OSNAP (Figure 4), which is in the process of deploying an observational network close to Greenland to measure the undersea flow in the critical north end of the AMOC.


Figure 4. The observational array being installed by OSNAP (Overturning in the Subpolar North Atlantic Program) will monitor surface and subsurface flow at several points over the far North Atlantic. Image credit: OSNAP.


The NAO at work
On top of longer-term climate change, there is some interesting decadal-scale variability in the mix. I checked in with oceanographer Steve Yeager (National Center for Atmospheric Research), who serves on the U.S. AMOC Science Team. Yeager agreed with Rahmstorf that the AMOC will tend to slow down over coming decades as a result of human-produced climate change. However, he added, “on the decadal time scale, you have the role of the North Atlantic Oscillation in slowing down or enhancing the AMOC.”

Although the North Atlantic Oscillation is notoriously variable from week to week, month to month, and year to year, it can lean toward one phase or the other for as long as 10 or 15 years (see Figure 5 below). When the NAO trends positive during the winter, as it did during most of the 1990s and early 2000s, it favors colder air staying cooped up in the polar and subpolar regions. This would tend to enhance the formation of bottom water in the Labrador Sea and boost the AMOC, and in fact the AMOC did strengthen in the 1990s. The NAO turned largely negative in the late 2000s and early 2010s, and this transition to more neutral/negative NAO conditions may have caused the AMOC to weaken substantially in the last decade, as suggested by RAPID data. In addition, the NAO-driven slowdown in ocean heat transport could have contributed to the extremely cold conditions observed recently in and near the North Atlantic blob, as discussed by Yeager in a recent paper in Geophysical Research Letters. The NAO has again averaged positive in three of the last four winters. Alas, Yeager noted, “we can’t predict the NAO. That’s the missing part of our predictability.”


Figure 5. The North Atlantic Oscillation (NAO), standardized and averaged across the January-to-March period for each year from 1950 to 2015. The black line is the five-year running mean. Based on monthly data, the 2016 value (not shown) will end up somewhere between 0.5 and 1.0. Image credit: NOAA/CPC.


What about the tropics?
Hurricane watchers may be wondering what all this means for the frequency of Atlantic tropical cyclones. In general, as demonstrated by Phil Klotzbach (Colorado State University) and colleagues, a stronger AMOC tends to lead to a more robust Atlantic hurricane season. There is typically a lag of several years before a switch in the AMOC influences sea-surface temperatures and hurricane activity. For example, the AMOC began strengthening in the early 1990s, followed by the spectacular onset of enhanced Atlantic hurricane activity in the mid-1990s. Likewise, the decline in the AMOC over the last decade has been followed by a ramp-down in Atlantic hurricane activity since 2013. In a Nature Geoscience paper last September, Klotzbach and colleagues argued that we may have already seen the end of the active cycle that began in the mid-1990s.

The potential arrival of La Niña later this year could prove favorable for Atlantic hurricanes, but the resilient cold blob may work in the opposite direction, according to Klotzbach. “When the far North Atlantic is cold, it tends to force wind and pressure patterns that then cool the tropical Atlantic,” he told me. “We've seen a significant cooling of the eastern subtropical Atlantic in recent weeks, 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 take a closer look at what 2016 may have in store next Thursday, when CSU issues its outlook for Atlantic hurricane activity.

Bob Henson


Climate Change Oceans Hurricane

March in the U.S.: Crazy Mild, Inconsistently Wet

By: Bob Henson , 4:51 PM GMT on April 06, 2016

After the mildest winter in U.S. history, March kept the theme going. Last month ended up as the 4th warmest March in records going back to 1895, according to the monthly analysis released on Wednesday by NOAA’s National Centers for Environmental Information. The warmth was much more consistent than usual for a strong El Niño year (see Figure 3), and more extensive than had been projected in February’s outlook for March. All 48 contiguous states (plus Alaska) were substantially milder than average. Every state from the Northern and Central Plains east to New York notched a top-ten warmest March (Figure 1), although only Alaska (not shown) had its warmest March on record. The nation’s most impressive burst of early-spring warmth arrived in Alaska on the last day of the month, when southeastern parts of the state basked in summerlike readings. A high of 71°F on March 31 at Klawock set a state record for March.


Figure 1. State-by-state temperature rankings for March 2016. Image credit: NOAA/NCEI.


Figure 2. State-by-state precipitation rankings for March 2016. Image credit: NOAA/NCEI.

Precipitation: big winners, big losers
For the nation as a whole, it was a reasonably moist month overall--the 26th wettest March on record for the 48 contiguous states--but the precipitation map itself is a checkerboard of anomalies (Figure 2). The most striking was in the Southwest: New Mexico had its driest March on record (the statewide average was just 0.06”), while its next-door neighbor, Texas, had its 12th wettest March (2.85”). This juxtaposition is a bit artificial, because most of the heavy rains in Texas were focused in the state’s eastern reaches, next to Louisiana (2nd wettest March on record) and Arkansas (3nd wettest). Likewise, although California had its 24th wettest March, most of that liquid gold fell in the northern and central parts of the state, with precious little in Southern California.

Some of the other impressively wet and dry states included Wisconsin (2nd wettest), Mississippi and Michigan (4th wettest), Washington (8th wettest), Virginia (7th driest), New Jersey and Arizona (9th driest), and Pennsylvania (10th driest).



Figure 3. March departures from average temperature (left) and precipitation (right) following the strongest El Niño events in the NOAA record, dating back to 1950: March 1958, 1966, 1973, 1983, and 1988. Image credit: NOAA/ESRL/PSD.


Drenched and parched: our pick locations for March
When it comes to dryness last month, it’s hard to top Arizona. Both Phoenix and Yuma failed to record a single drop of measurable rain--not even a trace. Phoenix’s last measurable rain was on January 31, although the city is a long way from toppling its record-long dry stretch (160 days, set in 1972).

Meanwhile, Memphis, TN, racked up 16.20” for the month. This smashes 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. Little Rock, AR, also got its wettest March by far since records began in 1875, with 12.33” this month beating out 10.43” (1897). And the 12.83” in Shreveport, LA, beat out 11.99” from March 1945, in records going all the way back to 1871. One of the hardest-hit areas was the Sabine River, which separates Louisiana and Texas. A record flood crest of 33.24 feet at Deweyville, TX--beating a record set in 1884--inundated the town of about 1200 residents for days. Deweyville schools have now been closed for several weeks, as the school system finds itself facing more than $10 million in uninsured losses.

Bob Henson


Figure 4. Homes in Deweyville, TX, are surrounded by floodwaters from the nearby Sabine River on March 15, 2016.

Climate Summaries

California’s Water Supply for 2016: Context is Everything

By: Bob Henson , 4:15 PM GMT on April 04, 2016

The pivotal end-of-March snow survey results are in from California’s Sierra Nevada--and whether the results are good or bad depends largely on your point of view. The current snowpack is about average when viewed from long-term climatology, bountiful against the backdrop of four years of punishing drought, and paltry next to what other “super” El Niño events have produced. Manual measurement on March 30 at Phillips Station, near Echo Summit (elevation 7382 feet), found that the snow water equivalent--the amount of water held in the soggy 58.4-inch snowpack--was 26 inches, or 97% of the long-term average for the date. Manual readings are collected each month at Phillips Station, largely as a ceremonial exercise and media event, with the end-of-March numbers closely watched because the snowpack typically peaks in late winter or early spring. A much more comprehensive picture of snowpack emerges from daily monitoring by more than 100 automated snow gauges across the entire Sierra Nevada. As of March 30, the statewide snow water equivalent was 24.4 inches, or 87% of average for the date. The percentage was down to 82% as of Monday.


Figure 1. What a difference a year makes: the Sierra snow survey being conducted at the Phillips course on April 1, 2015 (left), with California governor Jerry Brown, and on March 30, 2016, with Frank Gehrke, chief of the California Cooperative Snow Surveys Program for the California Department of Water Resources. Image credit: California Department of Water Resources (left); AP Photo/Rich Pedroncelli (right).

The two states of California, drought edition
There is no question that California’s water supplies are in far better shape now than a year ago. The April 1, 2015, snow survey took place on bare ground (Figure 1), with no snow at all present. Statewide, the snow content was only 5% of average, the lowest value since records began in 1950. Water supply agencies across the state faced their first-ever mandatory water restrictions in 2015. This February, the state water board extended those restrictions through October, although they will be re-evaluated later this month. Some users aren’t waiting. Citing the above-average water levels of Folsom Lake, the San Juan Water District has removed water restrictions for its 160,000 customers in central California as of March 23. The district is now calling only for a 10% voluntary reduction rather than the state-mandated 33% reduction.

Meanwhile, as of March 17, agricultural users in California are projected to receive 30% of water requested from the State Water Project supply this year. This compares to 20% in 2015 and 0% in 2014. Despite the improvement, we can expect many farmers and ranchers to continue drawing from California’s largely unregulated groundwater, a practice that has led to subsidence so dramatic--up to 2 inches per month in some areas--that it is detectable by NASA satellites.


Figure 2. Percent of average precipitation for the 180-day period from 12Z October 6, 2015, to April 3, 2016. For the Pacific states, the water year is commonly measured starting on October 1. Image credit: NOAA Advanced Hydrologic Prediction Service.


Where it’s been wet
The 2015-16 El Niño has produced buckets of rain and snow; it’s just that they’ve fallen a few hundred miles north of where one might have expected. Precipitation this winter has broken all-time records in Seattle (43.33” from October through March, already just a half-inch away from setting an October-April record). As seen in Figure 2, it’s been considerably wetter than average in far northern California and slightly above average through much of the San Francisco-to-Reno corridor. An unusually large fraction of northern California’s rain and snow either fell as rain or melted during midwinter warm spells, which has led to healthy replenishment of the state’s large northern reservoirs.

Toward Los Angeles and San Diego, the winter’s moisture has been much more disappointing. Los Angeles is currently sitting just below half of its typical total rainfall for the water year to date, with a mere 6.59” recorded from October 1 through April 3. The four climatologically wettest months of the year--December through March--actually came in drier for downtown L.A. in 2015-16 than in 2014-15 (6.13” vs. 6.67”). Late-summer rains helped give a boost to the full water-year totals if we extend them back to July 1, as noted by Chris Burt in his recent round-up of March and water-year precipitation across California. (The U.S. Geological Survey defines October 1 as the water-year start nationwide, but there are variations across California.) From this point into summer, a typical water year produces another 1.5” or so in Los Angeles and another 1” or so in San Diego. With models suggesting that an active subtropical jet stream will move into Southern California next week, it’s quite possible April will end up wetter than average--although L.A. would need close to its wettest April and/or May on record just to have a shot at an average water year for 2015-16.

The caveats of probability
Because there have been so few strong El Niños in modern records (1950 onward), and only two “super” events (1982-83 and 1997-98), experts stressed that a wet winter in California was highly probable but not guaranteed. The biggest surprise is that Southern California got the short end of the stick, as strong El Niños tend to be most reliably wet toward the south. In a study led by Andrew Hoell (NOAA Earth System Research Laboratory), published in Geophysical Research Letters in January, a multimodel ensemble of climate simulations keying off a century’s worth of data found that strong El Niño events significantly raise the odds of a wetter-than-average year statewide, but particularly across Southern California. The study found a more-than-90% chance of getting above-average precipitation in Southern California during a strong El Niño, which we’ve had in place this winter.

We should see this winter’s SoCal outcome juxtaposed against Hoell’s study as a reminder that even unlikely events do happen, a point emphasized by NOAA seasonal forecasters last month. “The results for 1982-83 and 1997-98 were probabilistic,” Hoell told me in an email this morning. Within the 130 simulations of the period 1979-2014 carried out for his study, Hoell added, “there were model simulations for 1982-83 and 1997-98 that resulted in exactly the same precipitation patterns that we saw this season. Assuming 1982-83 and 1997-98 are appropriate analogs (which is up for debate) then this event fell within the realm of possibility.” Preliminary model-based studies by Hoell and colleagues suggest this winter’s sea-surface temperature anomalies from El Niño were not as effective as those in 1982-83 and 1997-98 in generating wet conditions in California. It will be fascinating to see what insights emerge from the data collected by the El Niño Rapid Response Field Campaign, which spanned much of the February-March period that left Southern California largely high and dry.

The surprising aridity of the last few weeks has extended well into the Southwest U.S. Phoenix hasn’t seen a drop of measurable rain since January 31, although the city is a long way from its record-long dry stretch (160 days, set in 1972). Near Las Vegas, Lake Mead has recorded its lowest water levels for any January, February, and March since the lake was filled in the late 1930s. Further up the Colorado River, Lake Powell was at just 46% of full capacity on March 17. The snowpack upstream was at 94% of average, reflecting heavier winter snowfall in southwest Colorado than in neighboring areas.


Figure 3. The ruins of the Hannig Ice Cream Parlor are shown in the ghost town of St. Thomas on August 3, 2015, in the Lake Mead National Recreation Area, Nevada. The town was founded in 1865 by Mormon pioneers at the site where the Muddy River flowed into the Colorado River. At one point, it had about 500 settlers. The town was abandoned in 1938 after the construction of the Hoover Dam caused the Colorado River to rise. The area was once submerged in 60 feet of water but became entirely exposed as severe drought over the last 15 years has caused Lake Mead to drop to historic low levels. Image credit: Ethan Miller/Getty Images.


Figure 4. Departures from average in the height of the 500-mb surface for the three months from January through March 2016. The northeast Pacific is dominated by upper-level troughing (purple)--typical of an El Niño winter--while hints of a weak ridge (yellow) extend from the eastern tropical Pacific through the southwestern United States. Image credit: NOAA/ESL/PSD Map Room.

How California is going to extremes: a new analysis
A paper published last weekend in Science Advances shows that the upper-level features that drive California’s highly variable water-year precipitation have trended toward greater extremes in recent decades, with the patterns leading to dry years on the increase while wet patterns have held steady (or perhaps even increased as well). Led by Daniel Swain (Stanford University), the study analyzes October-to-May circulation patterns over the northeast Pacific for the years 1949 through 2015, examining how each water year compares to the five wettest, driest, coolest, and warmest. One ominous signal is a robust increase in the strength and persistence of upper-level ridging along the West Coast. The most dramatic recent example is the Ridiculously Resilient Ridge (RRR) that helped intensify California’s drought and record warmth. The RRR is gone, at least for the time being, but a lower-key, lower-latitude version may have played a role in this winter’s Southwestern dryness.

“It is definitely interesting that this winter featured some relatively subtle but persistent subtropical ridging between California and Hawaii,” Swain said in an email. “This is what kept Southern California so unexpectedly dry during this very strong El Nino winter, and prevented Northern California from being even wetter than it was.” Swain added: “Even though there were many more periods of active storminess in Northern California this winter than during recent drought winters, there were still some remarkably, unusually long stretches of dry and inactive weather caused by full-latitude West Coast ridging--even if it lacked the "resilience" of the RRR.”

The full paper is available through open access at Science Advances. There’s also a summary at the California Weather Blog. We’ll be back with a new post by Wednesday at the latest. Meanwhile, if you’re in the Midwest or Northeast, bundle up--it looks like a very chilly week ahead. Millions of people are under freeze warnings that extend across much of the Ohio Valley and a large chunk of the I-95 corridor from Washington, D.C., to New York.

Bob Henson

El Niño Drought

Maybelline to Sponsor Hurricane Eye Flights in 2016

By: Jeff Masters , 1:12 PM GMT on April 01, 2016

NOAA's Hurricane Hunters will have a new mission when they fly into the eyes of hurricanes this summer: issue plugs for their new corporate sponsor, eye makeup manufacturer Maybelline. At a joint NOAA/Maybelline press conference on April 1st, NOAA administrator Dr. Kathryn Sullivan lauded the agency's new sponsor, who outbid eyedrop manufacturer Visene for the exclusive sponsorship: "This remarkable partnership between NOAA and Maybelline is worth $1.23 million per year, which will enable the Hurricane Hunters to perform critical upgrades to their aging instrumentation, allowing them to continue to take the data crucial for predicting and understanding these most dangerous storms." Maybelline president David Greenberg added, "Maybelline's sponsorship of hurricane eye flights is a perfect public-private partnership blend. From Maybelline's perspective, what better way to draw attention to the power and beauty of eye makeup than to advertise Maybelline products from inside one of the most powerful and impressive eyes on the planet--the center of a mighty hurricanus maximus?"


Figure 1. NOAA's P-3 Orion hurricane hunter aircraft show off their new paint job for sponsor Maybelline.

New paint jobs for the hurricane hunters, and new additions to hurricane eye reports
The new sponsorship means that NOAA's two P-3 Orion hurricane hunter aircraft will be sporting new paint jobs. No longer will the aircraft carry NOAA's logo with the words, "U.S. Department of Commerce" on the sides; instead, the aircraft will carry the Maybelline logo, and sport lushly illustrated eyes done with Maybelline makeup on their tails. The sponsorship will also allow Maybelline to insert plugs for their products in the "Vortex" data messages that the aircraft transmit each time they penetrate the eye of a storm. A sample of Maybelline's new "Item Q" a hurricane hunter Vortex message is shown below:

URNT12 KWBC 102341
VORTEX DATA MESSAGE AL122015
A. 10/23:23:33Z
B. 33 deg 18 min N
071 deg 19 min W
C. 700 mb 3078 m
D. 42 kt
E. 059 deg 3 nm
F. 199 deg 56 kt
G. 060 deg 43 nm
H. 1000 mb
I. 8 C / 3070 m
J. 14 C / 3056 m
K. 8 C / NA
L. NA
M. NA
N. 1345 / 7
O. 1 / 4 nm
P. NOAA3 WB12A KATE OB 07
Q. ADD A SUBTLE SHIMMER, OR DARE TO GO BOLD WITH A FULL GLITTER MAYBELLINE EYE SHADOW

COMMENTS: MAX FL WIND 72 KT 113 / 49 NM 22:17:38Z
CNTR DROPSONDE SFC WIND 140 / 31 KTS

The new Item "Q" enhancements will be included for hurricane with both male and female names, since "we want to encourage people of all genders to experiment with Maybelline makeup", Maybelline president Greenberg said.

Happy April Fool's Day!

We'll have a new post by Monday--no fooling'.
Jeff Masters

Humor


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™

About

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