Meteorological winter runs from December 1st to February 28, for 90 days. The Winter of 2014-2015 was yet another cold one (the second in a row) although the character of the cold was sharply different from the long and persistent cold of 2013-2104. The winters of 2011-2012 and 2012-2013 were both mild to warm winters. Winter also featured below average precipitation, with the most pronounced dryness over the St. Louis area, easing to very slight dryness in the KC area and a very slightly above average winter precipitation total in Topeka. Snowfall through the end of February was below average from St, Louis through Kansas City to Topeka, but above average for SE Missouri and SW IL thanks to lower seasonal snowfall average and two significant February winter storms. The snowfall season continues to run (technically to June 30) to capture fall/spring snows in the total so we won’t have a season snowfall total until mid to late Spring. (Click on any of the images in this post to make them more readable).
Here is the statistic sheet for the three major reporting stations:
One thing that immediately is apparent is that this was a winter of contrasts. December and January were quite mild and February was so cold that it overpowered the warmth of the preceding two months. A different way to look at this is to check out a chart of the 31 day running mean (which is the difference from average) this smooths out the daily peaks and valleys and shows long term trends. The cold shot in November gave way to warmth through the Dec/Jan period (except for a quick cold shot in early January). Very strong and persistent cold took hold in February.
For comparison, check out the same chart for the winter of 2013-2014. That winter we had persistent and sustained cold from Fall right through into Spring. The cold was also deepest in February of that year. (That cold stretch lasted into April, 2014).
The main driver of the winter weather was the Pacific and the pool of warmer than average water which developed in late 2013.
Taking a look at a sample of upper air charts over the course of the winter tells the story.
In December, an enhanced Pacific jet stream brought the west coast much needed rain and pushed the ridge eastward from its November position off the west coast and into Alaska. This allowed a mild and moist Pacific flow to spread across the Plains and Midwest. The true cold was contained in the Arctic circle.
Here’s a snapshot of the jet stream level in December.
The pattern was stagnant and one thing we had were a lot of clouds. Check out the chart showing how cloudy the month was. Sunshine was not that far above the thin layer of clouds as shown by the Topeka KS sounding shown from December 11th.
The clouds kept overnight lows much higher than average while they kept daytime highs not so much above average. The net result was that the daily average temperature was much warmer than what is typical for December. December managed to squeeze out one minor snow event for KC and Topeka with the season’s most calendar day snow of 2.6″ in Kansas City. A weak wave aloft moved through grazing those areas with some light snows..while STL was bypassed and only had .2″ of snow for the whole month.
The overall month turned out very warm as shown by the temperature anomaly (difference from average) chart shown below. The chart is in degrees C, so multiply the value by 1.8 to get the equivalent in degrees F.
As January began, the prevailing pattern flipped to a much colder one. The Pacific jet retracted back across the Dateline and the ridge redeveloped along the west coast of North America and north into Alaska. That shut off the rain on the west coast and opened the door to cross-polar flow, releasing Arctic air back southwards under strong north-northwest flow aloft.
The season’s largest and strongest Arctic high (in terms of atmospheric pressure) moved into the center of the country by the end of the first week.
That brought the winter’s highest atmospheric pressures to the western district, including KC.
The coldest mornings of the winter were experienced across the western district, including KC. They would have been much colder, except for the lack of snow. -3F was the coldest temperature of the winter in KC on Jan 7 and Jan 8.
The cold pattern didn’t last long, the west coast ridge collapsed and returned eastward to the Rockies, with mild Pacific flow becoming re-established by the middle of the month.
Unlike the pattern in December, this was not such a cloudy weather pattern and allowed for some very warm temperatures under downslope flow across the Plains and into the western district. Several afternoons had highs in the 50s, 60s and 70s. The winter’s warmest temperature of 78F was recorded in Topeka, 73F in Kansas City.
The majority of the month was dry, although a moist system brought rains to the eastern district on the 3rd, before the Arctic air arrived. some minor icing events for SEMO/SWIL with the initial cold shot early in the month, with the majority of the precipitation falling as rain in the closing days of the month. Snow was limited with the major snows along the I-80 corridor and through the Great Lakes with Clipper lows. The northeastern U.S. meanwhile went from a snow drought to the beginnings of what would be all-time record snows for the winter season.
January temperatures wound up being below average for the Northeast, the south central states and parts of the Southeast. Temperatures were above average from our eastern district northwest through the Plains and most everywhere from the Rockies west. The chart is in degrees C, so multiply the value by 1.8 to get the equivalent in degrees F.
February brought about big changes as the ridge aloft rebuilt along the west coast and northward into Yukon and a deep upper low dropped into Hudson’s Bay. That brought strong NNW flow aloft and renewed Arctic surges for most of the month. That change, shown below, did not take shape right at the beginning of the month.
February opened with a quick cold shot, but quickly moderated to very mild conditions. The quick shot of cold followed a major snow along the I-80 corridor from Omaha to Ohio. That snow continued on to the Northeastern U.S.
Over the snowpack, cold surged south unimpeded for a very chilly morning on the second.
The cold, like the January episode, was brief with warmth re surging by the 7th, except over the new snowpack. Temperatures out in western Kansas actually reached the lower 80s, with mid 80s in the Panhandle.
Even while summer-like temperatures baked the Plains, the major pattern shift was underway. Bitter cold was building in Canada, as seen on this surface temperature anomaly chart. The greens, through purples show temperatures -10 to -45 degrees colder than average.
The first of the sustained cold shots arrived on the 12th with morning low temperatures crashing.
The warmth tried to put up a fight, but the Arctic overwhelmed the mild Pacific air. A wave riding up along the Arctic boundary to the south brought the season’s first snow of significance to the eastern district., with the heaviest snows along the Ohio Valley (as seen by the purple echoes). The western district was too deep in the cold to get in on major snows and instead received another minor event.
Here’s a look at the total snows as reported by the local NWS offices in and around the eastern district.
The western district has much lighter totals.
Some of the coldest weather of the season then targeted those areas with the deepest snow cover. This month it would be the eastern district’s turn to get the coldest temperatures of the winter. Morning lows on the 19th were bitterly cold.
Less snowcover and the timing of the passage of the high pressure center (it passed through in the daytime the afternoon of the 18th) prevented the western district from recording similar lows as the east.
The cold was widespread.
Another upper wave approached following this cold shot and set the stage for a wintry mix of precipitation the 20th-21st for the eastern district. That was followed by another Arctic front, the temperatures were not as cold as the earlier shot, but the wind chill values were, and wind chill advisories went up for much of the eastern district the night of the 22nd.
Another cold shot followed a weak clipper low through the region in the closing days of the month with overnight lows dropping back to the single digits – with subzero readings off to the north where fresh snow was on the ground.
This cold set the stage for February’s last snow event – again targeting STL/SEMO/SW IL and heavy snow missing KC again. Here’s the progress of the snow as it moved through the region.
Snow totals favored the east:
Here is the temperature anomaly (difference from average) for the last WEEK in February alone. The chart is in degrees C, so multiply the value by 1.8 to get the equivalent in degrees F.
Now, for the last half of the month.The chart is in degrees C, so multiply the value by 1.8 to get the equivalent in degrees F.
When the month was complete, temperatures were well below average everywhere east of the Rockies, with the core of the cold in the Great Lakes and Northeast. A very sharp transition to very warm conditions existed from the Front Range westward. The chart is in degrees C, so multiply the value by 1.8 to get the equivalent in degrees F.
That one powerfully cold month was enough to offset the Dec/Jan warmth for the Plains and Midwest, and really deepened the cold over the east. The coldest (relative to average) area was in New England where the snowpack was measured in feet. The warmest (relative to average) was in the inter-mountain west, The chart is in degrees C, so multiply the value by 1.8 to get the equivalent in degrees F.
Sea surface temperatures and the February pattern:
In terms of winter precipitation (liquid and melted snow) the majority of the eastern district was dry. The west was below average to slightly above average, but average winter precip in that area is only 2-6″ for the three month period, compared to 6-10″ for the same period in the east. 8-10″ fell in the southeast part of the eastern district, with 6-8″ central and 4-6″ northwest. In the west, a uniform 4-6″ of liquid or liquid equivalent precipitation was recorded.
This has left drought conditions bordering the western district to the south and west and the eastern district to the south and east.
The winter forecast:
Back on November 24th, we had a post on the winter outlook (click on November on the side bar and you can read the whole post).
Temps: We expected a cold winter, and that did verify, thanks mostly to a VERY COLD late February. We’d expected the cold to arrive sooner in December (it didn’t) and pull back briefly in January (it did, but the month was the reverse-mild but for one cold shot) and re-surge in February (that part did work out). If not for the intensity of the last half of Feb cold, winter would have been warmer than average.
Precip: The drier than average forecast has worked out (except in Topeka which was about a quarter inch above average).
Snow: The snowfall season won’t close yet, but the snowier winter has verified for SEMO/SW IL but we’re still behind (barely) in STL and well behind in KC. We’ll summarize that aspect of the winter season when the window for snow closes (around Easter).
Check out that post and you’ll be able to see how the major forecasting outlets fared in their winter outlooks.