Winter Storm

Winter Weather 2014-2015 Recap

The winter of 2014-15 served up some wild weather extremes but depending on where you lived in the U.S. they were at opposite ends of the spectrum.

Figure 1: NASA MODIS image Feb 3, 2015 showing the snow cover over the Northeast in the wake of Winter Storm LINUS, the third in a series of storms that blasted the Northeast with snow.

While parts of the West experienced some of their warmest and least snowy conditions on record, the East meanwhile suffered through one of the snowiest and at times coldest winters on record.

Much of this dichotomy had to do with the overall position of the jet stream across North America.

Figure 2a shows the 500mb height anomaly for the meteorological winter, or December through February. Note how much stronger the ridge/trof couplet across N. America was compared to normal. As a result of the more pronounced, or meridional, ridge/trough combination, the winter temperatures were much warmer overall in the Southwest and much colder in the Northeast. Those temperature anomalies are shown in Figure 2b.

Figure 2: Composite 500mb N. American height anomaly (2a) and surface temperature anomaly (2b) for the winter season as defined by the months of Dec-Jan-Feb 2014-15.

Even before winter officially began however, much of the U.S. was hit with a round of very cold temperatures and in one particular part of the nation, very heavy snowfall. This was due in part, of all things, a tropical weather system.

Typhoon Nuri, which reached the level of a category 5 typhoon in the tropical Pacific, moved into the higher latitudes of the North Pacific in early November, resulting in one of the worst storms on record to move through the Bering Sea. That system had a significant impact on the weather pattern downstream across North America as it sat over the Bering Sea, effectively pumping up a ridge over the West Coast of North America, which in turn produced a very deep trough over the rest of the continent. Figure 3 shows the 500mb pattern in the first week of November and the resulting pattern for the 10 days afterwards. Look at how that ridge built up over the west coast of North America.

Figure 3: 500mb composite heights for a) November 1-7 and b) November 8-20 showing the drastic change in the upper air pattern that took place in the second week in November 2014.

As a result, surface temperatures were much colder than normal for that time of the year across the U.S. as shown in Figure 4. This was put into perspective in a great blog by Chris Burt, Weather Channel Historian, when he discussed the change in temperature in Cheyenne, Wyoming from early to mid- November.

“It was the coldest November since 2000 for the contiguous U.S. (and 16th coldest on record) thanks to an exceptional arctic outbreak in the middle of the month," says Burt. "In Casper, Wyoming the temperature fell to -27°F (-32.8°C) on November 12th, its coldest on record for November. Amazingly, this was a drop of some -99°F (55°C) between November 1st, when the temperature peaked at 72°F (22.2°C) tying the record for the warmest November temperature ever observed in the city to November 12th when the monthly record low occurred.”

Figure 4: Composite surface temperature anomaly for the period November 8-20, 2014.

We would be remiss if we did not mention what some would call the biggest snowfall of the season for a populated area, that is the major lake-effect snow storm that hammered the suburbs just to the south of Buffalo, NY during the week before Thanksgiving. The lake-effect snow was due in part to the unseasonably cold air that set up over the Great Lakes due to the arctic outbreak. Two successive bouts of snow off a relatively warm and ice free Lake Erie produced phenomenal snowfall totals of as much as 70” in some places. The storm shut down a 132 mile stretch of the New York State Thruway and was accompanied by several rounds of lightning and snowfall rates as high as 6” per hour !! Figure 5 shows the total snowfall from this mesoscale snow storm and a view of the cloudband in all of its glory cutting across the south side of the city of Buffalo, NY.

Figure 5: Snowfall totals (left) and a view of the storm (right) that hammered Buffalo in November 2014.

The winter pattern relaxed somewhat during December and early January. However, winter really came in with a vengeance by mid to late January. During the late January through February time frame the meridional pattern became most pronounced, resulting in the coldest conditions in decades for much of the Northeast.

For parts of the Lower Great Lakes and New England the time frame from the last week of January through all of February produced some of the greatest total snowfall and coldest temperatures on record, many of which go back well over 100 years. In the West the opposite was true. The February state average temperature rankings reveal the entire Northeast experienced their second coldest February on record while at the same time out West they experienced their warmest February on record.

The seasonal snowfall exhibited a similar pattern in general between the West and Northeast. As an example, while the Sierra through the Cascades and the Wasatch experienced very low to record low snow pack conditions this past winter, some eastern locations saw their snowiest winters on record. The image below shows the 2014-15 seasonal snowfall in relation to above or below the normal for several cities across the U.S. As you can see, for the most part, locations west of the Mississippi were below normal while to the east were above normal. Some exceptions were along the Front Range of the Rockies where upslope flow in a few events provided locally heavy snowfall amounts. In addition, a series of snow storms in the mid-February through March time frame followed a southern track that favored snow for the Southern Plains in locations like Texas and Oklahoma.

Figure 8: 2014-15 snowfall (above or below normal) for various locations across the U.S. through May 15th. Values were calculated by rounding to the nearest 10% of normal. Data compiled from NWS records. — 2014-15 snowfall (above or below normal) for various locations across the U.S. through May 15th. Values were calculated by rounding to the nearest 10% of normal. Data compiled from NWS records.

The Northeast exhibited some amazing snowfall stats. Notable locations include Boston MA, where they set a seasonal snowfall record of 110.6”, surpassing their old mark of 107.6” set back in the winter of 1995-96. Much of New England set snowfall records as well. In Eastport ME, 132.5” of snow fell in only a 5-week period from late January through February with the snow depth topping out at over 6 ft. or 78.5”! Providence had the snowiest season on record at 76.2” and February was their 2nd snowiest month ever. Worcester set a record at 119.7” blowing away their previous record of 86.7”. In Bangor the seasonal total of 139.0” was the second highest but the snow depth actually got as high as 50” in late February. The incredible depths were a result of the cold air that was locked in across New England for all of February, not allowing any snow melt.

At The Weather Channel we name winter storms anticipated to impact the U.S. at a level of at least 2 million population or an area that covers at least 400,000 sq. km. Though not as prolific in terms of named storms as our two previous seasons, the winter of 2014-15 produced 22 named storms. This compares to 26 named storms during the 2013-14 season and 27 storms in 2012-13 as shown in Figure 10.

To get significant snowfall you need two main ingredients, temperatures that are cold enough to produce snow, and enough moisture that can be lifted into the atmosphere to be wrung out in the form of precipitation. That lift is generated on a large scale by Low pressure systems that track along the cold air. The track of these major winter weather systems has everything to do with the type of wintry weather and the amount of snow that falls.

Figure 11 shows all named storm tracks for the 2014-15 season. It is somewhat complicated to follow these tracks but there are some lessons we can take from plotting them. The Northeast was much snowier than normal, a result of some very juicy storms systems that moved through cold air on a track just south of New England which is a favorable track for heavy snow. The Midwest through Great Lakes also had significant snowfall. However, the Upper Midwest, including population centers from Milwaukee through Minneapolis had much less snowfall than normal. Their typical big snow producers are storms that originate from Colorado through Oklahoma, which often tap Gulf moisture then transport it northward into colder air. This past season the storms were more of the Clipper variety, coming out of Canada or the Northern Rockies. The Clippers are typically moisture starved and produce little snow until they get closer to the East Coast, where they can tap Atlantic moisture. The West of course had that huge ridge in place through the entire winter keeping most systems from tracking across the area to produce snow.

Total of named winter storms throughout the season for the past three seasons.

In the East, there were some fascinating “stories within the story” during the winter of 2014-15. I have separated part of the winter season into two sub-categories, a period that extended from late January to mid-February and one that extended from mid-February through early March.During the late January through mid-February period, when places like Boston and Eastport tallied up so much snowfall, no less than 5 separate storms impacted New England. Around February 12th, the overall large scale weather pattern changed somewhat across the nation as the ridge/trof couplet intensified, becoming even more meridional. The ridge built farther north and retrograded a bit and the trough over the eastern U.S. as shown in Figure 12.

This pattern resulted in two impacts; it pushed colder air much deeper south across the entire eastern half of the nation, and it drove the storm track much farther south with Lows developing off the Southern Rockies then moving through the Southeastern U.S. As a result, areas from the South through the Tennessee Valley were impacted by several winter systems. In Lexington, KY two separate storms, one in mid-February and another in early March combined to produce some record snowfalls. During Octavia 17.1” of snow fell in less than 2 days making this the heaviest two-day snow storm on record. It was the 6th snowiest winter, the 3rd snowiest February and 2nd snowiest March on record. In addition the temperature dropped as low as -18F on February 20th making it the 2nd coldest February day on record. Farther south in Texas, Dallas experienced 3 snow events in February and another in March. A comparison of the tracks before Valentine’s Day and after are shown below in Figures 13.

By mid-March the cold air retreated northward into Canada and the winter had pretty much abated across the continental U.S. However, even in May, a cold Upper Low moving from California across the Central Rockies put down nearly 2 feet of snow in parts of Colorado, South Dakota and Nebraska. So in summary I would say the winter of 2014-15 across the continental U.S. was almost polar opposite depending on whether you lived in the East or West. In particular a favorable storm track from mid-January through mid-February in the Northeast resulted in significant to record snowfall accumulating and from mid-February through early March, a very deep Upper level trof ensured an abundance of cold air which resulted in a lengthy period of high impact weather conditions consisting of deep snow pack and very cold temperatures. In a nutshell, the Northeast suffered from a long and severe period of wintry weather. In the West however, very little snowfall and record warmth not only significantly cut the ski season for many, it had much greater impacts on places like already drought stricken California. As we get into part two of the winter summary for 2014-15 we will discuss impacts from the 22 named storms.