Category 6™

Crunch Time Ahead for California Drought Relief

By: Bob Henson , 6:25 PM GMT on February 27, 2015

Californians are watching anxiously to see if a “Miracle March” or “Awesome April” salvages the worst snowpack season on record thus far in parts of the Sierra Nevada. Snow that piles up across the mountain range from autumn through spring furnishes more than 60% of the state’s water for consumer and agricultural use. Winter precipitation across California hasn’t been too far from average, but even more than usual, most of it has fallen in a relatively small number of wet storms, mainly in the first half of December and early February. The San Francisco Bay area saw its first bone-dry January in more than a century of weather records. Outside of December, which brought 17 wet days, San Francisco (downtown) has seen just 14 days of measurable rain since October 1.

Figure 1. Departures from normal for the height of the 500-millibar surface (in meters), averaged for the period Nov. 1 - Feb. 14 in 2013-14 (top) and 2014-15 (bottom). The positive departures (red) correspond to the location of the “Ridiculously Resilient Ridge”. Image credit: NOAA/ESRL, via California Weather Blog.

In many ways this winter resembles 2013-14, when the “Ridiculously Resilient Ridge” just offshore steered wet systems well north of California. This year’s upper-level features (Figure 1, right) have tended to park a little bit east of last year’s, enough to extent record warmth to the Great Basin and allow the occasional big storm to push its way onshore while smaller, weaker storms spin across Southern California. Upper-level ridging has strengthened over the past month, leading Daniel Swain (California Weather Blog) to proclaim the arrival of the Ridiculously Resilient Ridge, Redux.

A cardinal feature of this winter’s storms from California to Washington is their unusual warmth, which means that much of the water ran off from the Sierra as rain rather than accumulating as snow. Reservoirs in northern California got a healthy boost, now running from 70% - 100% of average for this time of year, but central California reservoirs are still hurting, most of them holding half at best of the seasonal average. The “reservoir” of water within snowpack is in far worse shape from the Sierra Nevada north through the Cascades, with most sites reporting 25% or less of the amount of water typically stored in snowpack at this time of year. Figure 2 illustrates the depleted state of snowfall in Yosemite National Park at elevations of more than 8,000 feet.

Figure 2. On February 19, the NWS office in Hanford, CA, tweeted this photo of a nearly snowless landscape, taken in Yosemite National Park at an elevation of 8,100 feet. Image credit: Elizabeth Christie.

California is entering its fourth consecutive year of widespread drought, as measured by the U.S. Drought Monitor, which takes into account soil conditions and streamflow as well as precipitation. This is the third multiyear drought in California since 2000, and as Figure 3 shows, it’s the worst of the three in terms of the geographic extent of the most dire drought categories. Each year of consecutive drought magnifies the impact, as progressively tougher adaptations must be called on. Last month, California’s State Water Project anticipated being able to meet only 15% of the contracted water needs of its customers (which include 25 million Californians) in 2015. Most of the burden will fall on agriculture, the main user of water in California, but cities will be affected as well. David Behar (San Francisco Public Utilities Commission) told me that his agency has asked customers to cut 10% from their total water use. “That’s happened across our service area in a very solid way. I think we’re seeing people take this drought very seriously,” he said. "Even a 20% cut would be tough, but we could weather it.” The bigger question is what might happen in a drought lasting a decade or longer: ”Every drought we live through this century will be a dry run, no pun intended, for what we might see in the future.”

Bob Henson

Figure 3. The percent of California’s land area at various stages of drought over the last 15 years, as defined by the U.S. Drought Monitor. Image credit: NWS/Hanford and


Memorable Snowfall Hits Deep South, Skirts Big Cities

By: Bob Henson , 6:48 PM GMT on February 26, 2015

A quick-moving snowstorm zipped from northeast Texas to southern Virginia in little more than 24 hours, leaving some parts of the Deep South with more snow than they’ve seen in decades. Rather than carving a deep trough in the eastern U.S., the upper-level energy that generated the snow tracked along the base of a broad pre-existing trough. This channeling of energy helped lead to a storm that had a vast extent from southwest to northeast but a narrow north-south gradient from substantial snow to little or no accumulation. The transition zone happened to fall across or near some of the largest cities of the South, which led to tough forecast challenges, just as we saw in the nor’easter last month that left New York City on its west edge.

Here are some of the broad variations in snowfall reported in and near metro areas across the South from the Wednesday/Thursday storm.

Little Rock, AR: 0 - 2”
Memphis, TN: 0 - 2”
Birmingham, AL: 0.5 - 4.0”
Atlanta, GA: 0 - 1”, with several inches across far northern suburbs
Charlotte, NC: 1 - 3”
Raleigh-Durham, NC: 3 - 5”
Norfolk, VA: 3 - 8”

Numerous cancellations and closures occurred across the Atlanta area on Wednesday night into Thursday, yet the storm produced less than an inch across the city, with larger amounts limited to the far north end of the metro area. When you zoom out and look at the big picture for northern Georgia (see Figure 1), the storm was very well forecast--but variations on the order of 15 miles, which are well within the error of current modeling systems, can make or break the outcome when they happen to fall across a city as populous as Atlanta. According to the University of Georgia’s Marshall Shepherd, this was a “great forecast, given where our capability currently lies . . . but if you expected something and didn’t get it, you may be upset.” Shepherd recently covered the ins and outs of snow prediction in the South in his Weather Underground blog.

Figure 1. A comparison of snow amounts predicted by the NWS/Atlanta office on Wednesday morning, Feb. 25 (left) and preliminary amounts as of Thursday morning (right). Although the forecast as a whole was quite accurate, the south edge of the heavier snow ended up just north of Atlanta instead of on top of the city. Image credit: NWS/Peachtree City, GA, courtesy Marshall Shepherd, University of Georgia.

Figure 2 (right). A youngster in Oxford, MS, savors a rare snowfall of significance. Image credit: wunderphotographer OxfordWeatherGeek.

The most impressive amounts for location and time of year occurred across central and northern Alabama and Mississippi. Tupelo, MS, saw 7.3”, its second-largest one-day snowfall on record (topped only by 8.0” on January 24, 1940). Huntsville, AL, also saw its second-snowiest day on record, with 8.1”; on Dec. 31, 1963, the city reported 15.7”. The region between Birmingham and Huntsville saw amounts exceeding 10” in spots, the heaviest observed there since the Superstorm of March 12-14, 1993. Weather Underground historian Christopher Burt discussed the greatest snows in the history of the South in this 2011 blog post.

A February to remember (or forget!)
Next week we’ll take a close look at national and regional statistics for February as a whole, which are bound to be impressive. In the meantime, here are a couple of samplers from the temperature realm:

--Syracuse, NY, is wrapping up its first month in 103 years of recordkeeping without a single measurement above freezing. The city touched 32°F only on February 4, with the next-warmest reading to date a mere 28°F. To make matters worse, Syracuse has dipped below 0°F a total of 21 days this winter, beating the record of 19 days set in 1947–48.

--Boston, MA, averaged 18.8°F for the period Feb. 1 - 25. That’s considerably lower than the February average so far in Aspen, CO (31.0°F), Anchorage, AK (24.9°F), and Moscow, Russia (26.1°F). All three of those cities are running well above their normal February temperatures, whereas Boston is usually about 10°F warmer than those three cities in February.

--In Salt Lake City, UT, the average daily high for Feb. 1 - 25 was 55.2°F. That’s the city’s long-term average high on the spring solstice in late March.

This week’s WunderPoster: Snow rollers
This week’s entry in our WunderPoster series (Figure 3, right) features snow rollers, one of the quirkiest phenomena observed in snow-prone regions. Sometimes up to two feet in diameter, these features are formed when a thin layer of wet snow atop ice or powdery snow gets disrupted by a windblown chunk of snow that pulls up some of the underlying snow in a cinnamon-roll-on-its-side fashion. All WunderPosters can be downloaded in formats suitable for posters or postcards.

Bob Henson

Figure 4. This fleet of snow rollers was captured on January 27, 2014, at Green Camp, Ohio. Image credit: wunderphotographer Gordanian.

Winter Weather

Are We Entering a New Period of Rapid Global Warming?

By: Bob Henson , 5:04 PM GMT on February 24, 2015

Residents of New England may understandably look back at 2015 as the year of their never-ending winter. For the planet as a whole, though, this year could stand out most for putting to rest the “hiatus”— the 15-year slowdown in atmospheric warming that gained intense scrutiny by pundits, scientists, and the public. While interesting in its own right, the hiatus garnered far more attention than it deserved as a purported sign that future global warming would be much less than expected. The slowdown was preceded by almost 20 years of dramatic global temperature rise, and with 2014 having set a new global record high, there are signs that another decade-plus period of intensified atmospheric warming may be at our doorstep.

The most compelling argument for a renewed surge in global air temperature is rooted in the Pacific Decadal Oscillation (PDO). This index tracks the fingerprint of sea surface temperature (SST) across the Pacific north of 20°N. A closely related index, the Interdecadal Pacific Oscillation (IPO), covers a larger swath of the entire Pacific. Both the PDO and IPO capture back-and-forth swings in the geography of Pacific SSTs that affect the exchange of heat between ocean and atmosphere (see Figure 1). We’ll use PDO as shorthand for both indexes in the following discussion.

The PDO typically leans toward a positive or negative state for more than a decade at a time. The positive phase, which features warmer-than-average SSTs along the U.S. West Coast, was dominant from the mid-1970s to the late 1990s. The PDO then flipped to a negative phase between about 1999 and 2013, with cooler-than-average SSTs along the West Coast. Figure 2 shows that even when a particular mode is favored, the PDO can still flip back to its opposite mode for periods of a few months or so.

Figure 1. Departures from average sea-surface temperature (degrees C) and wind (arrows) that typically prevail when the Pacific Decadal Oscillation is in its positive mode (left) and negative mode (right). Image credit: University of Washington.

It’s not clear exactly what drives the PDO, but in some ways it can be viewed as a geographically expanded version of the SST patterns created by El Niño and La Niña, averaged over a longer time period. (See Figure 2.) It’s well-established that El Niño can raise global temperature for a few months by several tenths of a degree Celsius, as warm water spreads over the eastern tropical Pacific and mixes with the overlying atmosphere. Likewise, La Niña can act to pull down global average temperature, as cooler-than-average water extends further west than usual across the tropical Pacific. The PDO mirrors these trends, but over longer periods. When the PDO is positive, there are more El Niño and fewer La Niña events, and heat stored in the ocean tends to be spread across a larger surface area, allowing it to enter the atmosphere more easily. When the PDO is negative, SSTs are below average across a larger area, and global air temperatures tend to be lower.

Figure 2. Typical warm and cool anomalies in sea-surface temperature during positive PDO years (left) and El Niño years (right). The patterns are similar, though with differences in intensity over some regions. The anomalies are reversed for negative PDO and La Niña years. Image credit: University of Washington Climate Impacts Group.

Figure 3 shows a striking connection between favored PDO modes (top) and global air temperature anomalies (bottom). The vast majority of atmospheric warming over the last century occurred during positive PDO phases, with negative PDOs tending to result in flat temperature trends. It’s easy to see how an atmospheric warming “hiatus” could occur during a negative PDO phase.

Figure 3. PDO values (top) and global air temperature anomalies (bottom). Gray shading indicates positive PDO periods, when atmospheric warming was most evident. The NOAA PDO values shown here vary slightly from those discussed in the article, which are calculated by the University of Washington. Image credit: Jerimiah Brown, Weather Underground. Data sources:NOAA (top) and NOAA/NCDC (bottom).

From the AMS meeting
The hiatus was discussed at length in a series of talks during the annual meeting of the American Meteorological Society last month in Phoenix. Jerry Meehl, from the National Center for Atmospheric Research (my former employer), gave a whirlwind 15-minute overview of hiatus-oriented research conducted over the last six years. Meehl’s talk can be viewed online. More than 20 papers have studied the hiatus and its links to the PDO/IPO, according to Matthew England (University of New South Wales). Most of the flattening of global temperature during the hiatus can be traced to cooler-than-average conditions over the eastern tropical Pacific, which pulled down global averages. An emerging theme is that natural, or internal, variability in the tropical Pacific can explain at least half of the hiatus. NCAR’s Clara Deser presented new modeling evidence along these lines (see video online). Other factors may be involved as well, including a series of weak volcanic eruptions that could explain a small part of the hiatus, according to a recent analysis by Ben Santer (Lawrence Livermore National Laboratory).

One crucial point is that global warming didn’t “stop” during the hiatus: the world’s oceans actually gained heat at an accelerated pace. Trade winds blew more strongly from east to west across the Pacific, consistent with the tendency toward La Niña conditions, as described in this open-access article by NCAR’s Kevin Trenberth and John Fasullo. Over parts of the central tropical Pacific, trade winds averaged about 3 mph stronger during 1999-2012 compared to 1976-1988. These speeds are higher than for any previous hiatus on record, bolstering the idea that other factors may have joined this negative PDO/IPO phase. The faster trade winds encouraged upwelling of cooler water to the east and helped deepen and strengthen the warm pool to the west—enough, in fact, to raise sea level around the Philippines by as much as 8 inches. Other parts of the deep ocean warmed as well. A new study led by Dean Roemmich (Scripps Institution of Oceanography) maps the areas of greatest ocean heating from 2006 to 2013 and finds that significant warming extended to depths of greater than 6600 feet.

What next for the PDO?
The PDO index, as calculated at the University of Washington, scored positive values during every month in 2014, the first such streak since 2003. By December it reached +2.51, the largest positive value for any December in records that go back to 1900. The January value from UW was 2.45, again a monthly record. (NOAA calculates its own PDO values through a closely related methodology.)

Because the PDO can flip modes for a year or more within its longer-term cycle, we don’t yet know whether a significant shift to a positive PDO phase has begun. If trade winds weaken throughout this year, and positive PDO values persist, that’ll be strong evidence that a new cycle is indeed under way. The last time we saw a two-year streak of positive values was in 1992-93. If this occurs, and assuming no spikes in major volcanic activity, we could expect greater rises in global temperature over the next 10 to 15 years than we’ve seen during the hiatus. In addition, we should watch for El Niño to make its presence known more often.

“I am inclined to think the hiatus is over, mainly based on the PDO index change,” NCAR’s Kevin Trenberth told me. While Matthew England isn’t ready to offer such a prediction, he emphasized that any post-hiatus global temperature rise is likely to be fairly rapid. Trenberth also commented on an interesting NOAA analysis (see Figure 4): “If one takes the global mean temperature from 1970 on, everything fits a linear trend quite well except 1998.”

Figure 4. When looking at global temperature over a full PDO cycle (1970s to 2010s), the overall rise becomes evident, despite the flattening observed in the last 15 years. Image credit: NOAA.

A record-strong El Niño occurred in 1998, providing an unusually powerful boost to global temperature and fueling years of subsequent declarations that “global warming stopped in 1998.” The record warmth of 2014 made it clear that global warming has no intention of stopping, and the next few years are likely to reinforce that point. Nevertheless, snowbound New Englanders, and millions of other easterners now dealing with record cold for so late in the year, may be wondering why eastern North America has seen so much cold and snow in the past few winters--especially this one--and how long that climatic quirk might continue. Stay tuned for a separate post on that topic.

Bob Henson

Climate Change

Reviewing Last Week's Remarkable Cold Wave

By: Bob Henson , 4:53 PM GMT on February 23, 2015

Unusually cold air will prevail across most of the Eastern U.S. for yet another week, making some inroads into the central states. Snow and ice continue to plague parts of the South and Atlantic: significant sleet and freezing rain are possible today from northeast Texas into Mississippi. Another round of wintry precipitation is likely midweek across parts of the mid-South, with the focus beginning to shift westward in a long-awaited pattern change by next weekend.

Apart from these events--and the record snow burying most of New England--it’s the cold that’s made its mark on the eastern United States this winter. A growing number of locations are within reach of their coldest February on record, and the last several days have been one of the most intense periods of cold on record for so late in the winter season in the Ohio Valley, Michigan, and the Southeast. A preliminary total of 398 daily record lows were set and 60 tied on Friday, February 20, according to NOAA’s Daily Weather Records site. That’s one of the largest single-day swarms of record lows in recent memory. (January 6, 2014, saw a similar number in its final tally, but that was after data had been received by 4007 sites, about twice as many as in Friday's preliminary total.) Saturday racked up another 209 daily record lows broken and 23 tied.

Figure 1. Sunshine illuminates icicles in the winter-swathed landscape of Plainville, Massachusetts, on Friday, February 20. Image credit: wunderphotographer PvilleGuy.

Did we just witness the most intense U.S. cold wave so late in the winter? At some locations, that may be true, according to Weather Underground’s weather historian, Christopher C. Burt. He points out that if you examine the month of February as a whole, there are some strong challengers that occurred only a few days earlier in the month than the cold wave just experienced. “Concord, New Hampshire set its all-time record low of –37°F on Feb. 16, 1943, as did Portland, Maine with -39°F on the same date,” Burt said. Then there was February 1936, when all-time state record lows were set at Parshall, North Dakota (–60°F on the 15th) and McIntosh, South Dakota (–58° on the 17th). More recently, Alpena, Michigan set its all-time record of –37° on Feb. 17, 1979, as did Escanaba (–32°F), and Marquette (–34°F). The next day, Old Forge, New York, set the all-time state record with –52°F, and Syracuse set an all-time low with –26°F. Burt’s take on the “coldest so late” debate: no matter whether it's early or late in February, you're still in meteorological winter. “I really don’t think one should talk about record-breaking late season cold for any event that takes place in February. I would posit that not until March should such discussions become relevant.” Burt adds that a close look at region-wide anomalies, rather than individual stations, is the way to find the rightful place for last week’s event next to other frigid February periods.

One challenge with assessing local records is that many of the nation’s oldest reporting stations have moved one or more times in their history. NOAA has made an effort to “thread” these datasets into continuous long-term records, but not all databases are complete and some aspects of station history can be difficult to unearth. Last Friday, we reported that Flint, MI, had tied its all-time record on Friday of -25°F, originally recorded on Jan. 18, 1976. Weather records expert Maximiliano Herrera wrote me to note that the records at the Flint airport go back to 1948, not 1921 as is commonly stated. Measurements were taken at a different location 7 miles from town from 1921 to 1948, and it turns out that Flint dipped to –28°F on Feb. 14, 1916, at another, still-earlier reporting site. Also, Jamestown, NY, tied rather than broke its all-time high, since the town reached –31°F on Jan. 5, 1904. More details pertaining to these and other records can be found at Herrera's comment (#1041) on Friday's blog post. Herrera maintains a comprehensive list of extreme temperature records for every nation in the world on his website.

Visit this week’s Portlight Strategies workshop via livestream
Portlight Strategies, Inc. and the Hampton Roads Regional Catastrophic Planning Team will present the Getting It Right Workshop this Tuesday and Wednesday, Feb. 22 - 23. The workshop will provide tools to facilitate full integration and inclusion in all aspects of emergency preparedness and response. Speakers include representatives from FEMA, the American Red Cross, and disability stakeholder organizations. The proceedings will be livestreamed starting at 9:00 AM EST on Tuesday. Founded and staffed by members of the Weather Underground community, Portlight Strategies is a 501(c)(3) organization that facilitates a variety of projects involving people with disabilities, including post-disaster relief work. Portlight's longest-running disaster recovery effort unfolded over 18 months following the devastation of Superstorm Sandy in the shore communities of New Jersey and parts of New York City.

Figure 2. The iconic Flatirons of Boulder, Colorado, on Monday morning, February 23. Although much of the western U.S. is dealing with drought, Boulder is having a record-snowy February, with 38.4" recorded through Monday morning at the local COOP observing station on the NIST/NOAA campus. Boulder snow records go back to 1899, with reliable COOP station data beginning in 1990. Image credit: Joshua Wurman, Center for Severe Weather Research.

Winter Weather

A Nation Divided: Heat and Cold Records Split the U.S.

By: Bob Henson , 5:50 PM GMT on February 20, 2015

This winter’s persistent U.S. gap between western warmth and eastern cold grew into a chasm this week. While unseasonable, unsettling mildness continues to bathe much of the West, one of the strongest February cold outbreaks in U.S. weather history--perhaps the worst and most widespread for so late in the winter--has taken hold from the Mississippi Valley eastward. Freezing temperatures pushed into parts of central Florida on Friday morning, with readings diving below the 0°F mark as far south as Tennessee. Cleveland, Washington, Baltimore, and Philadelphia all reported their coldest air since the 1990s. At least 500 daily record lows have been set or tied since Sunday, including several record lows for so late in the winter (including 9°F in Norfolk, VA, and –18°F in Lexington, KY, both on Friday) and a number of monthly lows. Crowning the list are the all-time record lows set or tied this week in four states:

Erie, PA: –18°F (tie], old record –18°F on Jan. 19, 1994; records began in 1873
Jamestown, NY (COOP station 4 miles ENE of town]: –31°F, old record –30°F on Feb. 17, 2015, and Feb. 12, 1979; records began in 1960
Lynchburg, VA: –11°F, old record –10°F on Jan. 21, 1985, and Feb. 5, 1996; records began in 1893
Flint, MI: –25°F [tie], old record –25°F on Jan. 18. 1976; records began in 1921

Gaylord, MI set an all-time lowest daily high at –5°F on Thursday, breaking the record of –4°F from January 27, 1986. Two unofficial lows of –39°F came in on Friday morning from automated reporting stations at Roscommon and Spincich Lake, Michigan.

Many cities in the Great Lakes and Northeast, and perhaps some entire states, are on target for the coldest February on record. Below is an update on three spots we examined in Monday’s blog post. With deep snow cover firmly in place, and the cold expected to persist through most if not all of next week, Bangor and Caribou should easily cruise to record-low monthly readings, while a brief warmup in Boston will likely kill its chances at a record-cold month.

Figure 1. A deep snowpack remained over New York and New England at 0600 GMT Friday, February 20, with lesser amounts prevailing from Missouri northeastward. Image credit: NWS/National Operational Hydrologic Remote Sensing Center.

A dangerous ice threat for the weekend
From the mid-South northward and eastward, extensive snow cover (Figure 1) is aiding and abetting the atmosphere’s plunge toward daily and monthly record lows. A new storm this weekend will bring a significant icing threat across a large area, with rich moisture surging atop very cold surface air that may be tougher than usual to flush out. Winter storm warnings are again in effect for parts of Arkansas, Tennessee, Alabama, and Georgia, with up to a half-inch of freezing rain possible in some areas Friday afternoon and evening before surface temperatures rise well above 32°F on Saturday. Precipitation will kick off as snow in many areas, including the East Coast from Washington to Boston, before transitioning to a wintry mix and eventually to rain, ahead of yet another Arctic blast early next week.

As the East shivers, the West simmers
While the eastern U.S. grapples with record cold, several Western cities are gunning for their warmest February on record, including those below. The last time Salt Lake City recorded a low temperature below the average for the date was on January 22.

Figure 2. Temperatures on Friday, February 20, are more than 30°F below average across much of the eastern United States, while above-average readings extend from western Mexico north to the Arctic coastline. Image credit: of Maine.

When have we seen this before?
The meridional jet-stream flow arcing north into Western Canada and dipping back south into the United States is striking in its persistence and strength, and there is a growing body of research into the effects of climate change and Arctic warming on jet-stream behavior. At the same time, there are some precedents for our current pattern, according to Weather Channel lead meteorologist Michael Palmer: “The highly amplified upper pattern with cross-polar flow that's been in place across North America this February is uncommon, but certainly not unprecedented. Some of the analogs that show up are February 1934, 1958, and 1963. In fact, much of that record cold from 1934 in the Northeast is being threatened with this current cold spell.” Showing how quickly things can change, the Dust Bowl year of 1934 went on to become the hottest year in U.S. weather history--a title it held until 1998.

Two severe tropical cyclones make landfall in Australia on the same day
Forecasters had their hands full at Australia’s Bureau of Meteorology early on Friday (Thursday US time), as Tropical Cyclones Lam and Marcia made landfall just six hours apart. Both systems intensified rapidly as they approached land.

Figure 3. The VIIRS scanning radiometer aboard a NASA satellite took this image of Marcia as it approached the coast at 1458 GMT Thursday, February 19. Image credit: NOAA/NASA RAMMB/CIRA.

Cyclone Lam made landfall about 500 km east of Darwin on Australia’s sparsely populated north-central coast around 1430 GMT Thursday (2:00 AM Friday local time). Several homes were reported destroyed in the town of Galiwinku, with water and power outages that could last up to a week. Marcia (Figure 4) struck a somewhat more populated area on the northeast coast near the small city of Yeppoon and Rockhampton at 2200 GMT Thursday (8:00 AM Friday local time), with power lines and trees down and some structural damage but no large-scale injuries reported. Satellite-estimated sustained winds at landfall were 105 mph for Lam and 125 mph for Marcia, with a gust to 129 mph reported at Middle Percy Island. Marcia is the strongest cyclone on record to strike the east coast of Australia so far south (around latitude 22°S). Cyclones heading for the Queensland coast, as Marcia did, often recurve at lower latitudes than hurricanes approaching the U.S. East Coast.

Figure 4. A visible satellite image shows the decaying Cyclone Lam (top center) and the intensifying Cyclone Marcia (right center) at 0033 GMT Thursday, February 19. Image credit: Japan Meteorological Agency.

According to climatologist Blair Trewin (Australian Bureau of Meteorology), this marks the first time since routine satellite coverage began in the 1970s that two severe tropical cyclones (sustained winds of at least 74 mph) made landfall in Australia within 24 hours of each other. In terms of geography and timing, it’s as if one hurricane hit Louisiana and another struck North Carolina later the same day. We can’t rule out same-day landfalls having happened in Australia prior to the 1970s, since the strength of many cyclones along the poorly sampled coast was likely underestimated in the pre-satellite era. Sea-surface temperatures were about 1-2°C above average in the regions where both Lam and Marcia developed. More details on the twin Aussie storms--referred to as a “cyclone sandwich” by locals, according to the Associated Press--can be found at the ABC live blogs on Lam and Marcia.

This week’s WunderPoster: Kelvin-Helmholtz Instability
The latest installment in our WunderPoster series (Figure 5, right) spotlights the graceful, symmetric clouds formed by Kelvin-Helmholtz instability. These shallow mid-level clouds can develop when a disturbance moves into two closely spaced layers of air that have strongly different densities and wind speeds, much like the interface between air and water that helps generate ocean waves. All WunderPosters can be downloaded in formats suitable for posters or postcards.

Bob Henson

Figure 6. Kelvin-Helmholtz instability produced these majestic clouds over Seattle, Washington. Image credit: wunderphotographer ChatNoirPhotographie.

Addendum: A Personal Cold Record for Dr. Jeff Masters
I’ve seen my share of cold temperatures, living in Michigan most of my life. But this morning, I set a personal record for coldest lifetime temperature when the mercury plunged to -29°F (-34°C) at my back yard Personal Weather Station in Highland, Michigan, 30 miles north of Ann Arbor. By six degrees, this is the coldest air this hardy northerner has experienced in his 54 years on the planet. I walked out to get the newspaper just after dawn, when it was -25°, to get the experience of the coldest air of my life. The air had a still clarity that the snow-reflected sun echoed brilliantly through. The cold made my nostrils feel all crinkly and tingly, and bit into my face with aching intensity. I tossed some water in the air to see if it would freeze before hitting the ground, but it wasn't cold enough for that. Now that I can say I’ve had the experience of -25° air, my California-based co-worker, Andria Stark, says that I should switch to the digital version of the newspaper in winter. But what fun is that? I like to always be aware of and connected to the atmosphere that surrounds us--though briefly in the case of -25° temperatures!

Have a great weekend, everyone!

Jeff Masters

Winter Weather

Second Warmest January on Record Globally

By: JeffMasters, 5:53 PM GMT on February 19, 2015

January 2015 was the second warmest January since record keeping began in 1880, said NOAA's National Climatic Data Center (NCDC) on Thursday. NASA also rated January 2015 as the 2nd warmest January on record, behind January 2007, which had the warmest departure from average of any month in recorded history. January 2015's near-record warmth continues a trend of very warm months for the planet--December 2014 was the warmest December on record, and 2014 was Earth's warmest calendar year on record. Global ocean temperatures during January 2015 were the 3rd warmest on record, and global land temperatures were the 2nd warmest on record. Global satellite-measured temperatures in January 2015 for the lowest 8 km of the atmosphere were the 7th or 5th warmest in the 37-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH), respectively.

Figure 1. Departure of temperature from average for January 2015, the 2nd warmest January for the globe since record keeping began in 1880. China had its warmest January on record, and record warmth was observed over much of the Caribbean and portions of Brazil and Mongolia. Image credit: National Climatic Data Center (NCDC) .

No billion-dollar weather disasters in January 2015
No billion-dollar weather-related disasters hit the Earth during January 2015, according to the January 2015 Catastrophe Report from insurance broker Aon Benfield. January 2015 joins November 2014 as the only months since January 2012 to go without a billion-dollar weather disaster. However, one nation experienced its most expensive natural disaster in its history in January 2015: Malawi, where two weeks of heavy rains triggered rampaging floods that killed at least 176 people and left 260,000 homeless. According to EM-DAT, the international disaster database, the floods of March 10, 1991 were the most expensive weather-related natural disaster in their history, with damages estimated at $24 million (1991 dollars.) The floods of 2015 may be ten times more expensive: Malawi requested humanitarian assistance of $430 million for recovery efforts from last month's disaster. The tropical disturbance that spawned these heavy rains moved over Mozambique on January 14, triggering flooding that killed at least 120 people there. The next day, the disturbance moved over the Mozambique Channel between Mozambique and Madagascar, becoming Tropical Storm Chedza, which hit Madagascar on January 16, killing 68 people on the island.

Figure 2. A bridge destroyed by flooding at Nchalo in Chikwawa, Malawi, the week of January 13, 2015. Image credit: Source: Department of Disaster Management Affairs, Malawi.

No official El Niño, but unusual warmth in Eastern Pacific
January 2015 officially featured neutral El Niño conditions in the equatorial Eastern Pacific, but sea surface temperatures were 0.5°C above average 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 an El Niño event to be declared. The warmth in the Niño3.4 region has continued into mid-February, and was still standing at 0.5°C above average this week. NOAA is continuing its El Niño Watch, giving a 50 - 60% chance of a weak El Niño event verifying for late winter and early spring. Nearly all international computer models are now projecting Niño3.4 temperatures to be well above the 0.5°C threshold by July, according to a roundup released this week by the Australian Bureau of Meteorology. However, model predictions are least likely to be accurate when issued during the period from February to May, as temperature contrasts across the tropical Pacific are normally weakening at that point.

Arctic sea ice falls to 3rd lowest January extent on record
Arctic sea ice extent during January 2015 was the 3rd lowest in the 36-year satellite record, according to the National Snow and Ice Data Center (NSIDC). During most of January, the Arctic Oscillation (AO) was in a strongly positive phase, bringing low sea level pressure to the Arctic and high pressure to the middle latitudes of the Northern Hemisphere. Typically, during the positive phase of the AO, surface winds push ice away from the shores of Siberia, leading to the formation of more young, thin ice that is prone to melting out in summer. The positive phase also tends to increase the transport of thick, multiyear ice out of the Arctic through Fram Strait. Thus, January's weather may be setting the stage for greater ice melt in the Arctic during the summer of 2015 than occurred in 2014.

Notable global heat and cold marks set for January 2015
Hottest temperature in the Southern Hemisphere: 49.0°C (120.2°F) at Marble Bar, Australia, January 23
Coldest temperature in the Southern Hemisphere: -48.2°C (-54.8°F) at Concordia, Antarctica, January 31
Hottest temperature in the Northern Hemisphere: 42.0°C (107.6°F) at Abu Na'Ama, Sudan, January 30
Coldest temperature in the Northern Hemisphere: -55.0°C (-67.0°F) at Selagoncy, Russia, January 5

Major stations that set new all-time heat or cold records set in January 2015
Cozzo Spadaro (Italy): min. -0.2°C [31.6°F), January 1
Ottosdal (South Africa): max. 40.0°C [104°F], January 6
M'Pouya (Congo-Brazzaville): min. 12.5°C [54.5°F], January 12
Afiamalu (Samoa): max. 31.2°C [88.2°F], January 15
Jabal Shamas (Oman): min. -9.7°C [14.5°F], January 20
Paynes Find (Australia): max. 48.0°C [118.4°F], January 21
Lamap Malekula (Vanuatu): max. 34.5°C [94.1°F], January 22

New all-time national and territorial heat records set or tied in 2015
Futuna Airport (Wallis and Futuna Territory, France) hit 35.5°C (95.9°F) on January 19

Samoa tied its national heat record with 36.5°C (97.7°F) on 20 January at Asau. Previously, the record was set at the same location in December 1977.

A big thanks goes to Maximiliano Herrera for providing the global heat and cold records. He maintains a comprehensive list of extreme temperature records for every nation in the world on his website.

Jeff Masters

Climate Summaries

Weather Underground Debuts Its Newest App: Storm

By: Bob Henson , 8:50 PM GMT on February 18, 2015

Fans of the widely-used Weather Underground app have cause to celebrate with today's release of the full-featured Storm app. The initial iOS release is downloadable free for iPhone and iPad through the App Store. Produced in a collaboration between WU and Intellicast, Storm builds on the usefulness and clean design of the main WU app, and the data and forecasting strengths of the two partners, to provide an array of new features designed with storm trackers and weather enthusiasts in mind.

High-definition radar: Storm provides access to data from the national network of NEXRAD radar sites at the top resolution available, with a razor-sharp 250 meters (800 feet) between data points. Users can view animations of past activity and extrapolations of current activity out to an hour ahead. When you select the radar nearest your location, a single-site sweeping feature displays reflectivity and velocity in near-real time.

Storm tracks: For each key area of current storm action identified by the app, Storm provides a strength rating, storm motion, precipitation rate, expected arrival times for the largest communities in the storm's path, any potential hazards (such as wind, hail, lightning, and tornadoes), and more.

Figure 1. The Storm app’s severe weather alert feature (shown here on the iPad) highlights real-time precipitation and lightning, along with any NWS watches, warnings, or advisories issued for the selected area.

Full-screen interactive map: The fully customizable Storm map interface allows you to display animated surface and jet-stream-level winds and fronts, as well as tropical data, severe weather alerts, and even earthquakes. I especially like the semi-transparent display of NWS watches, warnings, and advisories, which makes it easy to see where more than one type of alert is in effect. Also displayable: data from the WU network of more than 100,000 personal weather stations around the globe.

Customizable alerts and notifications: Users can be alerted of lightning, precipitation (within a 30-mile radius), and NWS warning polygons. The lightning alerts include a display of where cloud-to-ground lightning has struck in the last 15 minutes.

“Weather Underground and Intellicast have a long history of providing highly specialized weather information,” said Weather Underground manager Jim Menard “Recognizing the strengths of both companies, we decided to join forces to create the ultimate storm-tracking app.”

Figure 2. A single-site radar sweep on the Storm app’s iPhone interface.

Wunderground News

Intense New England Hurricanes Much More Numerous 340 to 1800 Years Ago

By: Jeff Masters , 6:43 PM GMT on February 17, 2015

Numerous Category 3 and 4 hurricanes frequently pounded New England during the first millennium, from the peak of the Roman Empire into the height of the Middle Ages, said a study accepted for publication this month in the open-access journal Earth’s Future, Climate Forcing of Unprecedented Intense-Hurricane Activity in the Last 2,000 Years. These prehistoric hurricanes were stronger than any hurricane documented to hit the region since the mid-1800s, and would be catastrophic if they hit the region today, according to Jeff Donnelly, a scientist at Woods Hole Oceanographic Institution (WHOI) in Massachusetts and lead author of the new paper. In a press release, Donnelly said, “We hope this study broadens our sense of what is possible and what we should expect in a warmer climate. We may need to begin planning for a category 3 hurricane landfall every decade or so rather than every 100 or 200 years.”

Figure 1. The storm surge from Category 2 Hurricane Carol in 1954 batters New England's Edgewood Yacht Club near Providence, Rhode Island. Image credit: NOAA Photo Library.

The paper is the latest contribution to the field of paleotempestology--the study of past tropical cyclone activity by means sediment deposits, cave speleothems, tree rings, coral deposits, as well as historical documentary records. In this case, the researchers took sediment cores from Salt Pond near Falmouth on Cape Cod, Massachusetts. The pond is separated from the ocean by a 1.3- to 1.8-meter (4.3- to 5.9-foot) high sand barrier. Over hundreds of years, storm surges from Category 2 and stronger hurricanes have deposited sediment over the barrier and into the pond. The scientists were able to calibrate the timing of the intense hurricane strikes by dating the layers from Category 2 Hurricane Bob of 1991, the 1675 (September 7) New England hurricane, and the Great Colonial Hurricane of 1635, which passed across southeastern New England and caused widespread damage consistent with a category 3 hurricane.

Figure 2. Scientists collect a sediment core from Salt Pond in Falmouth, Massachusetts, to study hurricane overwash deposits placed there by storm surges from intense hurricanes. The aluminum tube was vibrated into the muddy sediment at the bottom of the pond and then extracted with a hoist. Image Credit: WHOI

The prehistoric sediments showed that there were two periods of elevated intense hurricane activity on Cape Cod--from 150 to 1150, and from 1400 to 1675. Previous paleotempestology studies also found evidence of high hurricane activity during 150 - 1150 A.D. from the Caribbean to the Gulf Coast. Both time periods had unusually warm sea surface temperatures (SSTs) in the Main Development Region for hurricanes, from the Caribbean to the coast of Africa. Warm ocean temperatures in this region have been linked to increased intense hurricane activity by a number of recent research papers. In recent decades, ocean temperatures in the Main Development Region have surpassed the warmth of prehistoric levels, and these waters are expected to warm further over the next century as the climate heats up, suggesting that intense hurricane activity in New England may return to the levels of 340 to 1800 years ago. However, other factors besides warming SSTs will also shape what happens in the North Atlantic. For example, the pattern of ocean warming could bring more El Niño-style wind shear to the Atlantic, reducing hurricane activity. Still, New England would be wise to take heed of Donnelly's advice that we may need to begin planning for a category 3 hurricane landfall every decade or so rather than every 100 or 200 years.

Jeff Masters

Hurricane Climate Change

Mid-South, Mid-Atlantic Brace for Heavy Snow, Sleet, and Ice

By: Bob Henson , 4:34 PM GMT on February 16, 2015

A record-setting intrusion of Arctic air blasted through the eastern U.S. over the weekend, setting the stage for a bitter week that will remind many of the infamous cold stretch of January 2014. The biggest concern today and Tuesday is an upper-level impulse moving from Oklahoma to the Atlantic that will pull warm, moist low-level air from the Gulf of Mexico atop the surface-based Arctic air. Snow will stretch from southern Missouri to the Washington, D.C., area, with sleet and freezing rain extending from Arkansas to the Carolinas. At 6:21 am CST, law enforcement in Jasper, AR, reported 2 - 3” of sleet accumulation. The surface layer of cold air will generally remain thick enough to favor sleet over freezing rain, but significant freezing rain could occur in some areas; an ice storm warning has been issued for central Tennessee south of Nashville.

Parts of central Kentucky are getting their heaviest snow in years today, with as much as 15” expected. Washington, D.C., could get 6 - 10” or more of snow on Monday night, heaviest toward the south, although there may be large variations across the D.C. area; a small change in the storm track could bump the totals up or down by a big margin. As with the recent nor’easters, much of the snow in this cold storm will be on the fluffy side, with snow-to-liquid ratios of 15:1 to 20:1 adding to the potential accumulations. Tonight’s D.C. storm will be less intense but far better predicted than the unexpected, paralyzing President’s Day storm of 1979.

Figure 1. Ice forms along the shore of the Manhattan side of the East River in New York on Monday, February 16, after a weekend cold front sent temperatures into the single digits. Image credit: AP Photo/Peter Morgan.

The ferocity of the cold front that swept from the Midwest through the Northeast on Saturday was truly remarkable. As temperatures plummeted, winds gusted above 50 mph in at least nine states, taking down trees and knocking out power to hundreds of thousands. Hot Springs, VA, plunged from 30°F at 3 p.m EST to –1°F by midnight, and Washington’s Reagan National Airport tumbled from 44°F at 5 p.m. to 19°F by 11 p.m. Brief snow squalls and near-whiteout conditions were common just behind the front. One mesonet station near Fisherman’s Island, Virginia, reported a gust to 77 mph.

The powerful winds and cold air originated with an upper-level impulse that dove south from Greenland. Occasionally such an impulse will produce a “tropopause fold,” where a pool of air from very high levels gets pulled downward and tucked beneath the jet stream into the circulation of a developing storm. In this case, the fold was so dramatic over the Midwest that it brought the height of the tropopause down to about 8,000 feet from its typical midlatitude level in winter of around 35,000 feet. Such tropopause folds can help momentum from powerful jet-stream winds aloft to descend to the surface.

Figure 1. Winter Storm Neptune, as captured by the Suomi NPP satellite at 1700 GMT on Sunday, 15 February. The most intense precipitation is clustered at the far right of the image, extending north into southeast Canada (not shown). Image credit: Scott Bachmeier, CIMMS/University of Wisconsin.

The New England snow machine strikes again
It didn't take long for a powerhouse nor'easter to develop as the cold front plowed offshore Saturday night. This cyclone developed an intense but unusual structure, with at least three centers of circulation, each with a central pressure of less than 980 mb. The storm’s unusual evolution and its more easterly track produced less snow than expected in some areas: Portland, Maine, only reported 2.4” from Friday night through Sunday, while the far south and far southeast corners of the state each got more than a foot. Some of the storm’s worst impacts were in Canada’s Maritime Provinces: the wind-prone town of Grant Etang, Nova Scotia, recorded a peak gust of 109 mph on Sunday afternoon.

Figure 2. A puppy on a walk braves the epic accumulations in Cambridge, Massachusetts, on Sunday, February 15. Image credit: wunderphotographer salazar28.

Hitting the dubious snow jackpot once more were the eastern Massachusetts coast and parts of the Maine coast. The 16.2” at Boston's Logan Airport on Saturday and Sunday sent February into the record books as the city's snowiest month, with an amazing 58.5” of snow recorded through February 15 and nearly two weeks left to go. The renowned Blue Hill Observatory, just south of downtown, reported 45” on the ground at the summit of Great Blue Hill on Sunday morning—the greatest snow depth in the observatory’s 130-year history, topping the 43” recorded in March 1969. A CoCoRaHS site in Eastport, Maine, reported 78.5” on the ground Monday morning. Snow depth records are especially significant because techniques for measuring snow depth have changed little over the years, whereas the current practice of recording snowfall every six hours could give a slight edge to recent storms over those from long ago, when once-a-day measurements were more common. (Measuring snow at more frequent intervals leads to higher overall totals, since the snow has less chance to compact.)

Wind and cold champion: Mount Washington
New Hampshire’s Mount Washington Observatory, famed for having “The Worst Weather on Earth,” is living up to its slogan on the holiday created to honor its namesake. Just after midnight Sunday night, the temperature atop Mount Washington was –34°F, with sustained winds of 74 mph and an astoundingly low wind chill of –86°F. By 7:57 am EST, sustained winds had increased to 123 mph. It’s no wonder the mountaintop station issued this warning to would-be adventurers in its daily forecast on Sunday: “All [search and rescue] assistance if needed will have to come from below, as summit staff will not be able to assist in any way, shape, or form. A single injury will potentially put several lives at risk not just your own.”

Coldest February on record?
On Monday morning, Erie, PA, tied its all-time record low of –18°F, and Buffalo dipped to –10°F, its coldest temperature since January 6, 1996. Many eastern cities face a uncommonly frigid stretch for late February, especially as a second blast of Arctic air arrives later this week. Dozens of daily records could tumble, and some locations--especially mid-South locations with snow cover--will be in a good position to set records for lowest temperature so late in the winter. The currently predicted lows for Friday of –8°F in Lexington, KY, and –4°F in Nashville, TN, would do the trick. It will be tougher to set monthly lows, given that February is the region’s coldest month of the year. Still, this week could end up as the coldest of the 21st century for millions of people. With no sign of letup in the cold for at least a week, several Northeastern cities and states are within reach of their coldest February in a century or more of recordkeeping. Three examples:

Bob Henson

Figure 3. Thomas Mitchell took this shot in his neighbors’ kitchen in Beverly, Massachusetts on Sunday, February 15: “It's not just stuck to the windows, the snow bank is higher than the windows.” Image credit: wunderphotographer thomashmitchellcom.

Winter Weather

Coldest Day in Years On Tap for Ohio, New York

By: Bob Henson , 4:28 PM GMT on February 13, 2015

After focusing its wrath on New England for three weeks, winter is about to start expanding its reach. A packet of upper-level energy diving from the Canadian Arctic into the eastern U.S. this weekend will be accompanied by a strong surface high racing southward. The contrast in pressure between this high and the next powerful nor’easter off the New England coast will fuel an expansive area of howling northwest winds and dangerous cold. From northern Ohio across western New York, Sunday could be the coldest day recorded in at least 20 years and the coldest February day in many decades. This area is renowned for its snowy winters, but the same Great Lakes responsible for the snow also help buffer the region somewhat from the most extreme cold that’s found in the Upper Midwest and New England. Here are some NWS-predicted highs for Sunday, along with relevant records. Note that some cities could set daily highs for Sunday just after midnight on Saturday night, in which case the the numbers may end up less cold than shown here.

Cleveland, OH: 3°F
Last time a high was this cold: 2°F on Jan. 16, 2009
Lowest high for any day on record: –5°F on Feb. 9, 1899

Buffalo, NY: –2°F
Last time a high was this cold: –2°F on Jan. 17, 1982
Lowest high for any day on record: –3°F on Feb. 10, 1899 and Feb. 11, 1885

Rochester, NY: –2°F
Last time a high was this cold: –4°F on Jan. 17, 1982
Lowest high for any day on record: –4°F on Jan. 17, 1982

New York Central Park, NY: 17°F
Last time a high was this cold: 17°F on Jan. 22, 2014
Lowest high for any day on record: 2°F on Dec. 30, 1917

Temperatures are expected to dip to near or below 0°F across the New York metro area on Sunday night. The last time Central Park hit zero was on January 27, 1994. A shot of light to moderate snow will hit the coastal region from Philadelphia northward Saturday night and Sunday morning, with some heavier bursts possible in localized bands. The big concern is blowing snow and extremely high wind, with gusts to 60 mph possible (see Figure 1). Snow amounts will be much heavier from the Boston area northeastward. The NWS has posted blizzard watches from Saturday night through Sunday night for coastal counties from northern Massachusetts through Maine. Many areas will see a foot or more of new snow on top of 20 – 40” or more of existing snowpack, exacerbating already-serious impacts on roofing and infrastructure. Blowing snow will be a huge problem. The largest accumulations should be in southeastern Maine: 1 -2 feet are predicted to fall atop Bangor’s current snowpack of 45”. One station to watch for extreme wind this weekend is New Hampshire’s Mount Washington Observatory, which has already gusted to 89 mph at 9:45 AM EST on Friday morning.

Another winter storm appears likely to affect a much broader swath of the nation early next week, with a patchwork of snow, freezing rain, and sleet developing from Oklahoma and Texas to the Carolinas. This system may congeal into yet another bombshell nor’easter later in the week, perhaps accompanied by another shot of frigid air on par with this weekend’s, although uncertainty remains high at this point. Temperatures in New York may not reach the freezing mark for at least the next week.

Figure 1. The GFS model forecast issued at 0000 GMT Friday, 13 February, projects a powerful coastal low just east of Boston (minimum pressure contour of 976 mb) and a strong surface high north of Lake Huron (maximum pressure contour of 1042 mb) at 1200 GMT (7:00 AM EDT) Sunday, 15 February. The tightly packed isobars (black lines) between the two shows the extreme pressure gradient expected to generate dangerous wind chills across much of the Northeast, with blizzard conditions along the northern New England coast. Image credit: College of DuPage/Next Generation Weather Lab.

Severe weather season is at our doorstep
A few thunderstorms could develop on Monday or Tuesday near the cold front plowing into the Gulf Coast, although the threat of severe weather appears minimal. Some of the South’s worst tornadoes have occurred in February, as warm, moist Gulf air surges toward winter storms. Florida and Georgia held their annual severe weather awareness weeks February 2 – 6; Mississippi’s is now under way, and Louisiana and Alabama are slated for next week. It’s been a very quiet year for tornadoes thus far, with only 27 reported nationwide through February 11 compared to a year-to-date average of 68 for the period 2005 – 2014.

Figure 2. One of my favorite books as a child ("Weather: A Golden Guide"] included an illustration of a tornado dipping from mammatus clouds. Photos and videos have since made it clear that mammatus don’t produce twisters, but these clouds still generate a mysterious, ominous beauty. Mammatus are featured in this week’s new WunderPoster, which can be downloaded in formats suitable for posters or postcards. New posters will be unveiled each week through April.
See the WunderPosters site and our blog from last week for more details.

Figure 3. A spectacular field of mammatus on display west of Amarillo, Texas, on June 9, 2014. Image credit: Image credit: wunderphotographer tornadodude.

Atmospheric Struggles to Avoid Snowing in Massachusetts

By: Bob Henson , 4:39 PM GMT on February 12, 2015

Even the quiet days in between big storms are producing snowflakes during the amazing siege of winter weather that’s brought parts of eastern New England to a near-standstill. Wednesday brought a whiff of ocean-effect snow, the less-common Atlantic counterpart to the lake-effect snow that often hits cities like Buffalo and Syracuse. Both phenomena are driven by cold air passing over relatively warm water. Lake-effect snow is assisted by bands of converging air that develop when surface winds are aligned with the very linear lakes Erie and Ontario. The New England coast lacks such a geography, so ocean-effect snow is more rare, developing only when the atmospheric structure is highly favorable. Temperatures early Wednesday were in the low 20s along the Massachusetts coast, but as cold as 10°F less than 3000 feet above the surface. This led to enough instability for very shallow clouds and light snow, especially over Cape Cod. A strong inversion above this layer kept the clouds from growing any deeper, putting a lid on more intense snow.

Boston’s Logan Airport recorded eight hours of light snow but only 0.5” of accumulation. Traces of snow were observed as far northwest as suburban Andover--falling under blue sky, according to WSI’s Peter Neilley. “It was snowing lightly despite the fact that two-thirds of the sky was clear, and the southeastern third had just a thin cirrus overcast,” Neilley said. “On the very southeast horizon was some stratocumulus.”

Figure 1. A stripe of ocean-effect snow covered southeast Massachusetts and Rhode Island on Wednesday afternoon, February 11. Image credit: NOAA/College of DuPage.

No rest for the snow-weary
New Englanders continue to grapple with the aftermath of three major snowstorms--Juno, Linus, and Marcus--in less than three weeks. writer Charlotte Wilder captured the event’s emotional impact in “A Breakup Letter to Snow from the City of Boston” (right before Valentine’s Day, no less). Today’s ocean-effect snow pushed Boston’s total to 41.3” for the month--just 0.3” short of the February record--and 78.5” for the season. Since the first of the year, the city has set heaviest-snowfall records for intervals of 5, 7, 10, 14, 20, 30, and 40 days. (Thanks go to Michael Palmer and Kathryn Prociv at the Weather Channel for these statistics.)

Upper levels across North America remain locked in a pattern that supports more nor’easters, with the polar jet stream diving southward from Canada across the Midwest, then arcing across New England. The next winter storm will intensify into a powerhouse east of New England on Thursday and Friday, with surface pressure deepening quickly enough (more than 24 mb in 24 hours) to qualify the nor’easter as a “bomb.” It appears the storm will intensify just far enough out to sea to spare the coastline from anything more than continued ocean-effect snow. In its wake, though, the system will pull down another shot of frigid air across the Northeast, setting the stage for a potentially much more serious snow threat late in the weekend with the next nor’easter. Both the ECMWF and GFS models develop this second system near or north of the benchmark location of 40°N and 70°W, a good sign of potential impacts to New England. Temperatures will be cold enough to support another event with high snow-to-liquid ratios, perhaps 20-to-1 or greater, and the most likely focal point once again appears to be from eastern Massachusetts to coastal Maine. If the model trends continue, we could see rapid intensification of the surface low, with blizzard conditions and more than a foot of new snow quite possible over eastern New England (including the Boston area). While this week’s light snows mainly added insult to injury, a storm of the magnitude predicted by some model runs for this weekend could be a daunting blow to already-crippled parts of eastern Massachusetts.

Update (6:00 PM EST]: A blizzard watch has been issued for Saturday evening through Sunday evening for coastal counties of northern Massachusetts, New Hampshire, and Maine, including the cities of Boston and Portland. Widespread accumulations of more than a foot are expected, with wind gusts to 50 - 60 mph, very cold temperatures and wind chills, and extensive blowing snow,

Figure 2. Temperature anomalies (departures from average) of 30°F or more are possible across much of the central and eastern U.S. next week, as depicted in this 168-hour forecast from the GFS model valid at 0000 GMT on Thursday, February 19. Image credit: of Maine.

Winter’s coldest week coming up?
The upper-level low that’s plagued New England is projected to sharpen and shift westward next week, tapping extremely cold Arctic air. Several strong surface highs will likely move into the central U.S., much as we saw in early January, but this time bearing even more frigid temperatures. A band of significant snow, sleet, and/or freezing rain could materialize early next week from the mid-South to the mid-Atlantic. The GFS model, which has a cold bias on surface temperature, has pulled back from earlier predictions that would have approached all-time lows in some areas. In our warming winter climate, such records are increasingly hard to come by. Still, we can expect some daily records to be toppled or at least approached across much of the central and eastern U.S. over the next 7 to 10 days (see Figure 2), with some brutal wind chills possible. Already, wind chill advisories for values well below 0°F are in place across the Red River Valley of North Dakota and Minnesota, as well as much of Michigan, Ohio, Pennsylvania, New York, and western New England. Comparable warnings for extreme cold (wind chill) are in effect over much of Ontario and Quebec.

Figure 3. Snow depth at 0600 GMT on Thursday, February 12, averaged more than 20” across most of New England, with small pockets of more than 40” (purple hues) evident in several states. Image credit: NOAA/NWS National Operational Hydrologic Remote Sensing Center.

The best chance for truly historic U.S. cold this weekend or early next week could be over the very deep snowpack of New England, where depths of 10” to 30” or more are now widespread (see Figure 3). On a cold, clear night, snow cover enhances the loss of heat from the ground as radiational cooling predominates (also dubbed nocturnal cooling, as blogger Lee Grenci explains). A deep snowpack also brings the “surface” closer to the height of weather instrument shelters, where thermometers are located 4 - 6 feet above ground level. Since temperatures are coldest just above the top of the snow on nights of strong radiational cooling, deep snow can act to reduce temperatures at thermometer height. Such a setup in Oklahoma brought the nation’s most recent all-time state record low. A major winter storm dropped heavy snow across northeast Oklahoma on February 9, 2011, including a state-record 24-hour accumulation of 27” in the town of Spavinaw. The next morning, an Oklahoma Mesonet station in Nowata dipped to –31°F, breaking Oklahoma’s all-time record of –27°F (which had stood for 64 years). Just a week later, Nowata hit 75°F.

Bob Henson

Figure 4. The Alps of MIT: With more than 40 inches of snow blanketing the Boston area over the past two weeks, snow removal efforts on the campus of the Massachusetts Institute of Technology in Cambridge have engineered this new five-story-high mountain of snow. Image credit: Tom Gearty/MIT.

Winter Weather

Typhoon Higos Makes History in NW Pacific; Heavy Snow, Floods Pummel Southern Europe

By: Bob Henson , 3:50 PM GMT on February 11, 2015

With an unexpected burst of intensification on Monday, Typhoon Higos became the strongest tropical cyclone on record for so early in the year in the Northern Hemisphere. The compact typhoon dissipated quickly after its show of strength, having spun out its short life over an empty stretch of the Northwest Pacific roughly midway between the Marshall Islands and Northern Mariana Islands. The official peak intensity of Higos, as recorded by Joint Typhoon Warning Center (JWTC) was 105 kts (120 mph) at 0600 GMT on February 10, making it a Category 3. Satellite imagery suggests that Higos may have briefly spiked at Category 4 strength, with an outside chance of Category 5 strength, so the storm’s peak winds could be revised in later analyses. Two NASA satellites were in place to estimate rainfall rates below Higos.

Figure 1. NASA's Aqua satellite captured this visible image of Typhoon Higos at 0310 GMT on February 10, 2015. Image credit: NASA Goddard MODIS Rapid Response Team.

Figure 2. The satellite image at right of Higos, collected at 0301 GMT on February 10, 2015, shows a solid field of intense convection around the typhoon’s distinct eye. The typhoon’s intensity at this point or shortly thereafter may have been stronger than the officially recorded peak of 105 kts (120 mph). Image credit: NOAA, via @wxtrackercody.

Typhoons do form on occasion in February over the Northwest Pacific, with 36 tropical cyclones on record for the region since 1900 in NOAA’s Historical Hurricane Tracks website. However, these storms tend to develop late in the month, with their peak intensities often occurring in early March. Supertyphoon Mitag formed at the end of February 2002 and attained peak winds of 140 kts (160 mph) on March 5. The strongest intensity in the official record during February is 1970’s Typhoon Nancy, whose winds reached 120 kts (140 mph) on February 24. This also stands as a record for the entire Northern Hemisphere, since water temperatures are normally too cool and wind shear too strong to allow for hurricane development so early in the Northeast Pacific and North Atlantic.

Another noteworthy aspect of Higos is its position-–at peak intensity, it was more than 500 miles east of the track of any other February typhoon. The next closest is 2014’s Typhoon Faxai, although Faxai did not peak until early March. Sea-surface temperatures were close to 1°C warmer than average across the region where Higos developed (see Figure 3), part of a pattern of unusual warmth covering much of the western tropical Pacific.

Figure 3. Departures from average (anomalies) in sea-surface temperature (degrees C) for February 5, 2015, just before Typhoon Higos developed. Image credit: NOAA Office of Satellite and Product Operations.

Big snow, major flooding in Mediterranean Europe
While New England has been dealing with a spectacular onslaught of snow over the past week, southern Europe has gotten its own high-impact weather. The most devastating toll has actually been offshore: on Sunday, 29 migrants attempting to sail from Libya to Italy died of hypothermia after being rescued from the Mediterranean, and the United Nations now reports that at least 300 migrants in all appear to have drowned as several rubber dinghies capsized. Hundreds of motorists were rescued late last week after being trapped by as much as 15” of snow that fell across the Pyrenees and Cantabrian Mountains of far northern Spain. The much-touristed city of Bilboa received its heaviest snow since 1985, according to weather records researcher Maximiliano Herrera. Further east, the worst flooding in more than 40 years struck southern Albania last week. One district reported more than 11” of rain last week, more than double its average for the entire month. Tents, bedding, and winter clothes are en route from EU members Austria and Slovakia to help hundreds of flooding evacuees. Albanian prime minister Edi Rama asserted in an interview with the Guardian that deforestation and soil erosion contributed to the rainfall’s impact, and that poorly maintained dams and reservoirs could make matters worse.

I’ll have an update Thursday on the next round of bitter cold and potential snow heading for the Northeast U.S.

Bob Henson

Figure 4. Snow covers part of the cloisters at Roncesvalles Church, in the Pyrenees Mountains of northern Spain, on February 5. Image credit: AP Photo/Alvaro Barrientos.

tropical cyclone Winter Weather

Snow-Gripped in New England, Wet in the West, and Toasty in Between

By: Bob Henson , 3:44 PM GMT on February 09, 2015

The pincers of a warm-west/cold-east pattern took hold of the nation once again this weekend, and the contrast should only intensify over the next few days. The most dangerous weather unfolded across the far West to Northwest--with high wind and heavy rain--and over New York and New England, where the latest in a procession of winter storms is adding to snowfall totals measured in feet, not inches. The atmospheric river that’s doused the Pacific Coast states since late last week is making one final swing through the region, with rains expected to wind down over California by Monday night and across Oregon and Washington on Tuesday. Flooding and a landslide struck the town of Brinnon, Washington on Friday after more than 4” of rain fell. For the entire period Wednesday through 6 AM PST Monday, the towns of Petrolia, California, and Hoodsport, Washington reported 13.01” and 12.43", respectively. Rainfall amounts in major West Coast cities were healthy, if not overly impressive. For the month of February, San Francisco (airport) has recorded 2.02”, with 2.92” at Portland, Oregon, and 3.63” in Seattle, Washington. All three cities are now refreshingly above average for the water year to date, although long-range models suggest another dry spell of at least a week may be in the offing.

More extreme than the precipitation totals in the Western storm were the high winds, with power outages affecting more than 300,000 people. A 134-mph gust was reported at Slide Mountain, west of Reno, Nevada, at about 9600 feet. Downslope winds along the east slopes of the Sierra triggered a wildfire that destroyed 40 homes in a drought-stricken area near Swall Meadows, California, southeast of Yosemite National Park. The fire reportedly climbed to the unusually high snow line of around 8,000 feet. Powerful southerly winds that scoured the parched landscape of Nevada may explain the odd milk-colored rain that fell across parts of eastern Washington and Oregon on Friday.

Figure 1. As drenching rains fell on the west side of the Sierra Nevada, this fire raged on the east side near Bishop, California, on Friday, February 6. Nearly 11 square miles burned, 40 homes were lost, and 150 people were forced to evacuate. Image credit: AP Photo/Jim Stimson via CalFire.

Any relief for New England? The answer is snow
A relentless string of snowy storms is giving New England a midwinter of accumulations that could crush numerous records. Boston set a new mark on Monday for the most snow observed in a 30-day period. The city’s Logan International Airport recorded 61.6” from January 10 through 7 am EST on February 9, beating the previous 30-day record of 58.8” that fell from January 9 through February 7 during the infamous winter of 1978. The 2014-15 season needs to exceed 73.4” to make the city’s top-ten snowiest winters. As of 7 am EST Monday, Boston's seasonal total stood at 66.3". With another 2.5" of snow from Sunday's storm, the snow depth at Bangor, Maine hit 53 inches at 7 am EST Monday morning, which ties their all-time snow depth record set on Feb. 27 - Mar. 1, 1969. Bangor's average snow depth for February 9 is just 8.5 inches.

The latest storm is a long-duration event that’s depositing a foot or more across most of New England, but with small-scale bands expected to enhance the totals from the Boston area northward to New Hampshire. With 20” on the ground before this weekend’s storm, Boston could end up with an additional 18-24” by Tuesday. Yet another storm looms for Thursday, a powerful Nor’easter projected to intensify just offshore--but close enough that only a slight change in track could produce very heavy snow and high wind. Another Nor'easter could be in the offing on Sunday, though it is too early to assess the probabilities of this occurring. The city is already struggling to deal with the massive logistics of snow removal; schools will be closed Monday and Tuesday. In a press conference on Sunday, Boston mayor Martin Walsh asked residents for patience and vigilance. “No other city, no other mayor, has to deal with this much snow,” Walsh said. ”Maybe in Buffalo or Alaska." The coldest temperatures so far this year could plague New England late this week into early next week, with much of the region dipping well below 0°F for lows and struggling to get out of the single digits (if even that) for highs.

Figure 2. It’s not the best weather for biking in Boston right now, as residents grapple with ever-growing roadside snowbanks. Photo credit: AP Photo/Charles Krupa.

A February thaw for millions
The contrast between the Northeast and the rest of the contiguous U.S. was especially sharp on Sunday, as many states from the mid-Atlantic to the Rockies basked in unseasonable mildness. Record daily highs were set or tied from Washington D.C. (68°F) to Salt Lake City (64°, its fourth daily record in a row). Salt Lake City is running close to 20°F above average for the first eight days of February, and hit 68° on both Friday and Saturday--by far the their earliest-in-year 68-degree highs ever recorded, and just one degree shy of their all-time February record of 69°, set on February 28, 1972. However, another state capital--Augusta, Maine--is more than 12°F below average, at a frigid 8.5°F. On Saturday, temperatures soared to 73°F in Rapid City, SD; 80°F at McCook, NE; 82°F in Hill City, KS; and 83°F at Lamar, CO. Another large batch of records is likely on Monday before temperatures moderate somewhat.

While the temperatures above are far more pleasant than the brutal conditions in New England, they’re actually more extreme when set against local averages for early February. The latest statistics from NOAA bear out the fact that 2015 has been on the mild, dry side for the lower 48 as a whole. Last month was the 24th warmest and 18th driest January in 121 years of record-keeping, according to NOAA’s National Climatic Data Center. Record highs and lows paint an even more stark picture. NCDC’s records page showed on Sunday that for the year to date, the nation had seen 2040 daily record highs but just 360 daily record lows. The ratio is even more lopsided for monthly highs (198) vs. monthly lows (4).

Bob Henson

Figure 3. Temperatures have stayed above normal levels (green area in image) in Salt Lake City on every day since January 5. Even the lows have failed to dip below normal daytime highs for a solid week, from February 2 through February 8. Pink bars show records highs for the date, while light blue bars are record lows. Image credit: NWS/Salt Lake City.

Winter Weather Flood Heat

Carbon Dioxide, Congress, and the President -- 50 Years Ago

By: Bob Henson , 4:32 PM GMT on February 07, 2015

The human-induced rise in greenhouse gases typically heats up the room when it’s discussed on Capitol Hill. Yet the issue scarcely gained notice when it was brought to the attention of Congress by President Lyndon Johnson a half-century ago this weekend. On February 8, 1965, Johnson delivered a “Special Message to the Congress on Conservation and Restoration of Natural Beauty.” The bulk of the message dealt with land and water conservation, highway beautification, and other goals now considered mainstream. Tucked midway through the text was this observation: “Large-scale pollution of air and waterways is no respecter of political boundaries, and its effects extend far beyond those who cause it. Air pollution is no longer confined to isolated places. This generation has altered the composition of the atmosphere on a global scale through radioactive materials and a steady increase in carbon dioxide from the burning of fossil fuels.”

Figure 1. Scenes like this--from an industrial section of Cleveland, Ohio, circa 1973--were once commonplace in the largest U.S. cities. Image credit: Frank J. Aleksandrowicz/National Archives and Records Administration.

Johnson’s message came years before passage of the Clean Air Act and Clean Water Act, at a time when air- and stream-fouling pollutants were far more prevalent than today and litter was a national scourge yet to be seriously tackled. As the public discussion turned to these assorted but related threats in the late 1960s, carbon dioxide remained far in the background, but concern among scientists been building for years. A crucial paper by Roger Revelle and Hans Seuss (Scripps Institution of Oceanography), published in the journal Tellus in February 1957, noted the rise of carbon dioxide levels and warned: “Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future. Within a few centuries we are returning to the atmosphere and oceans the concentrated organic carbon stored in sedimentary rocks over hundreds of millions of years.”

A few months after that paper, Charles David Keeling launched the routine measurements of carbon dioxide at Mauna Loa that continue today. The data quickly made it clear that CO2 in the global atmosphere was increasing year over year. The topic even gained enough traction for famed director Frank Capra (“It’s a Wonderful Life”) to include a reference to to it in an hour-long TV special in 1958, “The Unchained Goddess.” Part of the nine-episode Bell Laboratory Science Series, which aired between 1956 and 1964, the program focused mainly on weather but warned of the ultimate potential for dire effects from the unchecked growth of carbon dioxide. It noted that, at the time, more than 6 billion tons of carbon dioxide were being emitted each year due to human activity. Emissions in 2013 totalled more than 39 billion tons (36 billion metric tons).

Video 1. Here’s a dramatic one-minute excerpt from the 1958 film by director Frank Capra illustrating the expected effects of high-end global warming. Capra was a scientist who graduated from California Institute of Technology in 1918 and did many science films for education while working for Bell Labs.

I touched base this week with Spencer Weart, author of the superb book “The Discovery of Global Warming,” whose entire contents (plus extra material) are available online through the American Institute of Physics. Weart pointed out: “Revelle and Keeling already understood that the carbon dioxide buildup could have dangerous long-term impacts, such as a devastating rise of sea level.” A few months after Johnson’s message to Congress, a presidential advisory committee produced “Restoring the Quality of Our Environment.” This report (see PDF) included a section calling out possible effects of an increase in atmospheric carbon dioxide, including melting of the Antarctic ice cap, warming of sea water, increased acidity of freshwater, and an increase in photosynthesis. The report concluded, rather dryly, that “ . . . climatic changes that may be produced by the increased CO2 content could be deleterious from the point of view of human beings.”

For more on Johnson’s message to Congress, and a related conversation that was tape-recorded in the White House just days earlier, see this excellent Daily Climate article by Marianne Lavelle.

Bob Henson

Climate Change Politics Climate Change

Powerful Atmospheric River Set to Blast the U.S. West Coast

By: Bob Henson , 12:01 AM GMT on February 06, 2015

From San Francisco to Seattle, millions are watching and waiting for the arrival of 2015’s first major atmospheric river event. The impending AR will likely be the most intensely observed in weather history, thanks to an armada of instruments deployed across California and the Northeast Pacific for the CalWater 2015 study. (See my Tuesday post for more details.) The AR will plow into the coast Thursday night and Friday, with its core gradually sagging southward into central California by Friday afternoon into Saturday morning. Assuming the rain holds off through midnight Thursday night, downtown San Francisco will have just edged out November-December 1976 for the city’s second-longest midwinter dry spell on record (43 dry days). The only longer dry period is 60 days, from November 17, 1876 through January 15, 1877.

Multiple periods of heavy rain are on tap for much of northern California, western Oregon, and western Washington, with rainfall rates exceeding 1”/hour and a few thunderstorms possible in California. The most intense rain and snow can be expected along the west slopes of mountain ranges, as extremely strong low- to mid-level winds packed with tropical moisture strike the mountains. Water vapor at the core of the AR is at more than 200% of average seasonal values. Wind gusts may exceed 60 mph near the coast and at high altitudes. Even stronger gusts above 100 mph are possible along the crest of the Sierra; high wind warnings have also been posted for the range’s eastern slope, where mountain-wave features could produce gusts of 60 - 80 mph.

Figure 1. There’s no missing the powerful atmospheric river on this map of projected flow at 700 hPa (700 mb) at 1500 GMT on Friday, February 6. Image credit:

Forecasters still expect a large area of 5 - 10” of rain over the next several days (see Figure 2 below), and today’s models suggest that heavy rains may extend southward from the San Francisco Bay area. West-facing slopes of the central and northern Sierra should also get several inches of beneficial rain, with as much as 3 feet of dense “Sierra cement” snow at the highest elevations. Snow levels in the Sierra will remain very high for a midwinter storm (generally above 8000 feet) until somewhat colder air arrives with the concluding system on Sunday and Monday, when elevations down to Lake Tahoe could see several inches of snow. Illustrating the warmth ahead of this system, Reno set a daily record high of 70°F on Thursday; only three other times has the city has reached 70°F so early in the calendar year.

Overall, the rains from this event should help replenish reservoirs in central California and provide welcome greening of vegetation across a large area. The critical Sierra snowpack (which provides about a third of California water supply) may only see modest improvement from its very low levels for this time of year. Little rain from this system will fall on Southern California, where the multiyear drought has had its firmest grip.

Widespread, severe river flooding is not expected with this system, but flood watches are in effect for most of coastal northern California and southern Oregon, as well as western Washington, where the Skokomish River is already near flood stage. Some localized flooding can be expected with the most intense downpours on Friday into Saturday; that risk may rise as soils saturate and rivers fill up (see Figure 3 below). Rains should be on the decrease later in the weekend before a final blast arrives with a colder, more well-defined upper-level storm on Sunday and Monday.

Bob Henson

Figure 2. Projected five-day precipitation totals from 0000 GMT Friday, February 6, to 0000 GMT Wednesday, February 11. Image credit: NOAA/NCEP/Weather Prediction Center.

Figure 3. From drought to deluge: the Russian River at Guerneville, California, is projected to swell from its current level of 5 feet to a peak of 26.3 feet by next Monday, February 9. Image credit: NWS Advanced Hydrologic Prediction Service.

winter weather

Put Your Weather Enthusiasm on Display with a WunderPoster

By: Bob Henson , 5:13 PM GMT on February 05, 2015

In our pixel-packed, circuit-crammed world, there’s something to be said for a beautifully rendered print poster that you can enjoy each day on the wall of your home or office. Starting today, we’re going to help you decorate in meteorological style with the debut of our WunderPoster series. Our first batch of 13 posters was produced by a crackerjack team of Weather Underground designers that includes Jerimiah Brown, Dan Fein, Lauren Moyer, Jennifer Potter, Skyler Rexrode, Prooshat Saberi, Aryn Shelander, and Mike Tiscareno. Each Thursday from now through the end of April, you’ll find a new poster on the WunderPosters home page. This new project is one way we’re celebrating our 20th anniversary: Weather Underground was launched in 1995 as the first public-oriented online weather service. We were around #2000 in the sequential list of Internet domains granted worldwide. Today, that list is up to more than 241 million.

Figure 1 (right). Our debut WunderPoster puts the spotlight on advection fog, the hallmark weather feature of Weather Underground’s home base in the San Francisco Bay.

Each WunderPoster will include a capsule description of the weather phenomenon illustrated. The placeholders now on the WunderPosters site provide a hint of what you’ll see appearing over the next few weeks: mammatus, sundogs, frost flowers, lenticular clouds, and much more. WunderPosters can be downloaded in a high-resolution format (2400 x 3200 pixels) that allows for high-quality printing at sizes up to 8" x 10”. There’s also a handy double-sided postcard option.

You might correctly guess from today’s kickoff entry that our WunderArtists are paying homage to the distinctive poster artwork produced in the 1930s and early 1940s by the Works Progress Administration. A major part of the New Deal, the WPA is best known for the thousands of parks, schools, and other public amenities it built (many of which still stand). Another part of WPA was an arts program that put designers to work on murals, photographs, and other creations. This included some 2 million posters in an astounding 35,000 designs, illustrating everything from national parks to theatrical productions. The Library of Congress has more than 900 original WPA posters in its permanent collection, all available online.

Want to get in on the ground floor of our newest endeavor? We'll soon be launching a contest to find the inspiration for future WunderPosters. Stay tuned for details.

I'll post an update on the West Coast atmospheric river later today.

Bob Henson

Figure 2. Advection fog on the White River in Arkansas, produced by 90°F air passing over cold spring water. Image credit: wunderphotographer StormTrain.

Wunderground News

Atmospheric River Heads for California as a Massive Field Study Gears Up

By: Bob Henson , 6:30 PM GMT on February 03, 2015

Relief is on the way for drought-stricken parts of the U.S. West later this week, as an intense atmospheric river (AR) takes aim. This ribbon of deep moisture and strong wind will move onshore by Thursday night, kicking off a multiday series of downpours from roughly the northern half of California into the Pacific Northwest. The impending AR will likely be the most intensely observed in weather history, thanks to an armada of instruments deployed across California and the Northeast Pacific for a two-month interagency study called CalWater 2015. The project’s goals are to improve prediction of ARs affecting California and to assess the importance of aerosols (airborne particles) in shaping rainfall patterns across the region.

Figure 1. NOAA’s Ronald H. Brown research vessel is among the research platforms now being deployed to study atmospheric rivers in the CalWater 2015 project. Image credit: NOAA.

ARs are well worth getting a handle on, since they play an outsized role in both drought relief and flooding across California. It’s been estimated that 25 - 50% of California’s water supply is derived from AR events. As research intensified on ARs in the 1990s, scientists recognized that the rain-bearing moisture channel often called the “pineapple express”--extending from Hawaii to California--was just one example of a global phenomenon. More than 90% of all the water vapor that flows into midlatitudes from the tropics is channeled by ARs, which span just 10% of the latitudinal band at 35°N. When we look at a global loop of satellite-derived moisture content, ARs show up as bright filaments, stretching poleward like taffy being pulled from the perennial band of rich moisture that encircles the tropics. When a midlatitude storm draws in moisture from an emerging AR, the moisture becomes further concentrated as winds converge just ahead of the associated cold front. ARs can extend more than 1000 miles long but average only about 200 - 400 miles wide. Along with the the classic “pineapple express” pattern, ARs can take on a variety of other shapes and trajectories, which adds complexity to predicting how they’ll behave.

Computer forecast models can now spot many ARs five or more days before they threaten the U.S. West Coast, but there are often big uncertainties among models in the strength, position, and timing of each AR event. Many of the question marks arise simply because of the limited data available from the Pacific Ocean. Passive microwave sensors can estimate the total amount of water vapor located over the Pacific, but upper-level winds are more difficult to gauge by satellite. The first CalWater study in 2010 shed light on some of these uncertainties, as well as the importance of aerosols in either stimulating or suppressing rain and snow at various altitudes. A separate project called HIPPO showed that a surprisingly large amount of aerosols can reach the North Pacific from Asia, which implies they might be able to influence the evolution of some ARs. This year, CalWater is expanding its sights with a beefier set of observing platforms. They include three aircraft (P-3 and Gulfstream IV “hurricane hunters” from NOAA and a Gulfstream I from the U.S. Department of Energy) along with NOAA’s Ronald H. Brown research vessel, which will launch weather balloons and employ its newly upgraded dual-polarization radar. Specialized instruments aboard the aircraft will measure cloud microphysics and aerosol properties.

Figure 2. Cumulative 168-hour (7-day) precipitation from the GFS model run starting at 1200 GMT Tuesday, February 3. Image credit: NOAA.

The outlook for this week’s AR
Light rain is already pushing into western Oregon and Washington today and Wednesday ahead of the core AR event. The newly upgraded GFS model, whose resolution was sharpened to 13 kilometers last month, is the most bullish on heavy rain for the upcoming AR. The 12Z Tuesday output (Figure 2) delivers more than 5” of rain to the north part of the Bay Area through the weekend, with the potential for 5” – 10” or more and very strong winds in and near the coastal range through far northern California and southwest Oregon. More than 10” of liquid equivalent could also over mountainous parts of Washington. Hefty precipitation totals are also expected along the central and northern Sierra Nevada in California, with available water vapor close to record-high amounts for February. Unfortunately for the snowpack, temperatures through the weekend will be warm enough to keep most of the bounty in the form of rain below 7000 - 8000 feet, with a more general lowering of snow levels only toward the end of the multiday bout of storminess. The European and NAM models produce substantially lower precipitation amounts for this system, so it’ll be worth watching to see if the upgraded GFS comes through with the best overall precipitation forecast, as it did with last week’s Blizzard of 2015 (Juno) in the Northeast. Model resolution plays a key role in predicting heavy precipitation, especially in mountainous areas where the local topography can be better resolved.

Allen White, a research meteorologist with NOAA and a mission scientist for CalWater 2015, reports that the NOAA G-IV will be transecting the atmospheric river offshore on Wednesday, perhaps followed by the P-3 on Thursday with possible flight paths above the Ron Brown and over the coast near Bodega Bay. Flights on Friday would likely be over California, where the aircraft data would supplement an array of vertically pointing precipitation profilers and enhanced rain gauges. Meanwhile, the G-1 will focus on aerosol-related missions, including the impacts of long-range dust transport. “Having all these observing assets available is a huge bonus,” White told me. “We can now observe the AR and the precipitation it generates from above, below, and throughout. This requires a huge forecasting and coordination effort and highlights a very successful interagency collaboration among federal, state, and local agencies, as well as academia.”

A 2014 open access paper in Frontiers in Earth Science provides a good overview of AR research for readers comfortable with some relatively technical content.

Figure 3. Based on GFS model output from 1200 GMT Tuesday, February 3, NOAA’s automated AR detection tool indicates that a plume of enhanced moisture will be headed squarely for northern California at 1200 GMT Friday, February 6. Colors show integrated vapor transport in units of kilograms per meter per second, with arrows indicating the direction and strength of transport. The model indicates that the core of the AR will carry more than 1000 kilograms (about 2200 pounds) of water vapor every second across every meter of ocean that’s oriented perpendicular to the flow. Atmospheric rivers are generally defined by values of at least 250 kg/m/s. Image credit: NOAA Earth System Laboratory.

Digging out in the Midwest and Northeast--for now, at least
The sprawling winter storm dubbed Linus turned out to be an overachiever along much of its west-to-east course from the northern Great Plains to New England. With blizzard warnings posted on Sunday, Chicago ended up with its fifth largest snowstorm on record (19.3”) and the most snow for any calendar day in February (16.2”). Detroit racked up its third largest storm on record with 16.7”, the most observed in any event since 1974. On Monday, New Yorkers again found themselves on the margins of a winter storm, this time laboring through a sloppy sequence of snow, sleet, rain, freezing rain, and snow that left patches of treacherous ice on Monday night. Meanwhile, much of eastern New England is reeling from the one-two punch of heavy snows last week and again this week, with an intervening lighter storm only adding insult to injury. From January 24 through February 2, Boston racked up 47.9” of snow; according to the Weather Channel’s Nick Wiltgen, this is the largest total for any ten-day period on record in Boston. The town of Lunenburg, about 45 miles west of Boston, did even better (or worse) as it notched 36.6” and 19.7” from Juno and Linus, respectively, for a grand total of 56.3” of snowfall. Bangor, Maine, reported 45" of snow on the ground Tuesday morning, the most since a record 53" in February-March 1969. A weak clipper will bring more light snow to the Midwest and Northeast later this week, followed by a shot of bitter cold. Looking further out, winter-weary and wary New Englanders could get pummeled by yet another significant snow by the weekend, although model guidance so far has been inconsistent.

Bob Henson

Figure 3. An evocative depiction of snow without end, taken Monday evening, February 2, at Kennebunk, Maine: “It was a very dark and gloomy day, without big fluffy flakes or brightness in the sky. Temps have remained in the single digits, so the snow has remained small and granular as well. Thought I'd try one more shot while there was a bit of daylight left.” Photo credit: wunderphotographer Kennebunker.

Winter Weather Atmospheric Phenomena

Groundhog Says: 6 More Weeks of Winter; Top-Five Snowstorm Belts Chicago, Detroit

By: Jeff Masters , 1:45 PM GMT on February 02, 2015

A classic mid-winter snowstorm is sweeping across the nation, dumping heavy snow along a swath 2,000 miles long from Colorado to Maine. On Sunday the storm blasted Chicago with heavy snow and strong winds that created near-whiteout blizzard conditions, bringing the city its fifth heaviest snow on record--19.3". More than 18" of snow plastered Northwest Indiana and Southwest Michigan, with a storm-maximum snowfall amount of 20" observed in Kalamazoo, Michigan. Here in Southeast Michigan, my snow shoveling muscles are sore today after dealing with the 16.7" the storm dumped on Detroit--the city's third heaviest snowfall on record. By Monday morning, the storm had moved on to Ohio, hitting Cleveland with 4.7". The biggest totals during the remainder of the storm's trek are expected in snow-weary Massachusetts, with snow amounts near 12" expected in Boston. That city received 24.4" of snow from last week's blizzard; several locations in Central Massachusetts near Worcester received 36" of snow, and are expecting another 12" from this storm.

Figure 1. Westbound I-88 near IL Rte 53 in Lisle, Illinois on Sunday 2/1/15 @3:56pm CST. Image credit: Wunderphotographer Hammelmom.

Chicago's Five Biggest Snowstorms Since 1871:
1. 23.0 inches Jan 26-27, 1967
2. 21.6 inches Jan 1-3, 1999
3. 21.2 inches Jan 31-Feb 2, 2011
4. 20.3 inches Jan 12-14, 1979
5. 19.3 inches Jan. 31-Feb 2, 2015

Detroit's Five Biggest Snowstorms Since 1880:
1. 24.5 inches Apr 6, 1886
2. 19.3 inches Dec 1-2, 1974
3. 16.7 inches Feb 1-2, 2015
4. 16.1 inches, Mar 4-5, 1900
5. 14.0 inches, Feb 28-Mar 1, 1900

Groundhog Says: Six More Weeks of Winter!
In Punxsutawney, Pennsylvania, home of the world's most famous prognosticating rodent, Punxsutawney Phil, 3" of snow had fallen by Sunday evening, and on Monday morning the town was beset by a lovely wintry mix of snow, rain and freezing rain that only a hibernating groundhog could love. However, the skies cleared briefly at sunrise on Monday morning, allowing Punxsutawney Phil to see his shadow and make his usual fearless prognostication for the remainder of winter:

“Forecasts abound on the Internet,
But I, Punxsutawney Phil, am still your best bet,
Yes, A shadow I see, you can start to twitter,
Hashtag: Six More Weeks of Winter!”

Figure 2. Canada's famous albino groundhog named Wiarton Willy from the town of Wiarton, Ontario. Willie failed to see his shadow at dawn Monday, so his prediction calls for an early end to winter--in late February. In New York City, groundhog forecaster Staten Island Chuck also predicted an early end to winter. Image credit: wunderphotographer pincollector1.

How did this this crazy tradition start?
It all started in Europe, centuries ago, when February 2 was a holiday called Candlemas (much like Halloween and May Day, Candlemas is another ancient holiday positioned near the halfway point between solstice and equinox.) On Candlemas, people prayed for mild weather for the remainder of winter. The superstition arose that if a hibernating badger woke up and saw its shadow on Candlemas, there would be six more weeks of severe winter weather. When Europeans settled the New World, they didn't find any badgers. So, instead of building wooden badgers, they decided to use native groundhogs (aka the woodchuck, land beaver, or whistlepig) as their prognosticating rodent.

The Groundhog Oscillation: convincing evidence of climate change!
According to a 2001 article published in the prestigious Annals of Improbable Research, "The Groundhog Oscillation: Evidence of Global Change", Punxsutawney Phil's forecasts have shown a high variability since 1980. This pattern, part of the larger "Groundhog Oscillation" or GO cycle, is convincing evidence of human-caused climate change.

Grading Phil's forecasts
NOAA’s National Climatic Data Center (NCDC) analyzed Punxsutawney Phil’s forecasts over the past 27 years (thanks to Doyle Rice of USA Today for pointing this out.) If we evaluate just the twelve years when the departure of February and March temperatures from average over the contiguous U.S. were both of the same sign, Phil had five correct forecasts and seven blown forecasts. NOAA concludes that “It really isn't a 'bright' idea to take a measure such as a groundhog's shadow and use it as a predictive meteorological tool for the entire United States.”

What the pros say
The latest 16-day run of the GFS model shows the jet stream remaining farther south than usual over the eastern half of the U.S. during the coming two weeks, with our omnipresent "Ridiculously Resilient Ridge" of high pressure anchored over the Western U.S. This pattern will result in colder than average temperatures over the eastern half of the country, and warmer than average temperatures over the western half. The latest 1-month forecast from NOAA's Climate Prediction Center (CPC) shows this pattern dominating through February. The latest seasonal forecast from agrees with this idea, but predicts that a warmer than average pattern may emerge over the Midwest and South during the last week of February, with below average temperatures confined to just the Northeast. Heading into March and April, WSI predicts warmer than average conditions across the northern tier of states, and cooler than average over the South (except for California, which will remain warm.) The latest 3-month forecasts for February - April from Columbia University's International Research Institute for Climate and Society and from CPC show the odds for cold weather easing over the Eastern U.S. during the period February - April, with near-equal chances of above or below-average temperatures. They forecast increased odds of cooler than average weather over Texas, with increased odds of warmer than average weather along the West Coast.

Figure 3. Temperature outlook for February 2015, as predicted by NOAA's Climate Prediction Center (CPC) on January 31, 2015. A continuation of the cool in the east, warm in the west pattern is favored.

Jeff Masters

Winter Weather

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

Category 6™


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