The Winter of 2012-2013: The winter that almost wasn’t

On the heels of the non-winter of 2011-2012 when dry and mild weather and record low snow totals were observed, many people were certain they would be required to pay back with interest their good fortune for the Winter of 2012-2013. The surprising truth is they almost got away with “not paying the bill”!  The party ended mid February when old man winter placed a hefty guest check on the table. It also presents us with an example of why forecasts for an above average winter temperature wise does not always equate to little or no snow.

The Spring and Summer of 2012 had been very warm and very dry with a flash drought developing over most of the Midwest. The remains of Hurricane Isaac and heavy rains broke the drought and ushered in a welcome period of below average temperatures which took us through mid Fall.  The pattern flipped at that point and a period of very warm dry weather returned.  This warm dry pattern would continue for nearly 120 days.  Transient cold shots interrupted the warm weather but overall the trend was warm.  A sustained change to colder weather began mid February and would last the next 100 days (as shown on the graphic below).

Temperatures ran well above average for most of the (meteorological) Winter of 2012-2013, with sharp cooling the last few weeks.

Temperatures ran well above average for most of the (meteorological) Winter of 2012-2013, with sharp cooling the last few weeks.

The Arctic and North Atlantic Oscillations were mostly negative as meteorological winter began, which are typically cold signals for the Midwest, yet the mild weather continued.  The image below shows the state of these indices during meteorological winter (Dec-Feb).

Analysis of the state of the Arctic & North Atlantic Oscillation for 2012-2013. Both were in negative territory for most of meteorological winter, except for a period in January. Even so, temperatures remained well above average despite the negative indices. This is a good illustration that even when negative, cold snowy weather is not a slam-dunk.

Analysis of the state of the Arctic & North Atlantic Oscillation for 2012-2013. Both were in negative territory for most of meteorological winter, except for a period in January. Even so, temperatures remained well above average despite the negative indices. This is a good illustration that even when negative, cold snowy weather is not a slam-dunk.

When the Arctic Oscillation is negative, the weather patterns depicted in the graphic below are more likely to occur, although for a majority of the winter, they did not.

"Classic" or typical weather patterns when the Arctic Oscillation is in negative mode. A weaker jet stream and fractured polar vortex allow large north-south swings in the river of air that is the polar jet. Blocking near Greenland is typically established which funnels cold air out of the Arctic into the central and eastern U.S.  The subtropical jet, when active, can interact with the cold for major winter storms.

“Classic” or typical weather patterns when the Arctic Oscillation is in negative mode. A weaker jet stream and fractured polar vortex allow large north-south swings in the river of air that is the polar jet. Blocking near Greenland is typically established which funnels cold air out of the Arctic into the central and eastern U.S. The subtropical jet, when active, can interact with the cold for major winter storms.

By the middle of February, winter was notably absent and people were beginning to think that another non-winter was going into the record books and the bill could be put off for another year.  The graphic below shows St. Louis’ monthly snow totals for Winter 2012-2013.  As of February 1st, the start of the last month of (meteorological) Winter, only 3″ of snow had fallen.  Take away February and March, that would have been the winter total.

Three significant snowstorms, two  in February and one in March brought almost all of St. Louis's significant snow.  Without those three storms, only 3" of measurable snow would have fallen that winter.

Three significant snowstorms, two in February and one in March brought almost all of St. Louis’s significant snow. Without those three storms, only 3″ of measurable snow would have fallen that winter.

This graphic illustrates the same for Kansas City. 4.7″ of snow fell to February 1st.  Well below average but 0.8″ higher than the record low snow of 2011-2012. Take away February and March and the unusual record breaking half inch of May snow and that would have been Kansas City’s winter total.

Two major snowstorms brought a majority of Kansas City's snow in the winter of 2012-2013, both in late February followed by a third in March. Measurable snow was recorded in May, the season's latest ever. 31.7" of snow fell which was nearly twice the 18.8" average.

Two major snowstorms brought a majority of Kansas City’s snow in the winter of 2012-2013, both in late February followed by a third in March. Measurable snow was recorded in May, the season’s latest ever. 31.7″ of snow fell which was nearly twice the 18.8″ average.

The pattern change that brought in the cooler weather also helped bring in the snowfall.  Some areas such as SE Missouri and S Illinois missed all of these February & March major storms, but they were hit by significant winter storms in December which brought their snow totals to near or above average.

As shown on the above chart, Kansas City recorded 20.5″ of snow in February and 6″ in March.  St. Louis 10.6″ and 14.3″ in March. These two month totals exceeded the average annual snow for both cities.

The map below shows the average annual snowfall for the Midwest.  In this part of the Midwest. our annual snow totals are within striking distance of 2 or 3 significant winter storms or one severe winter storm. This is particularly true with southern areas of the region where annual snow totals are less than a foot. The winter of 2012-1013 was a prime example; it only took two to three storms to turn an almost snowless winter to a very snowy winter and one of those storms technically occurred in Spring.

Average annual snowfall totals based upon the 1981-2010 climate period for the Midwest.

Average annual snowfall totals based upon the 1981-2010 climate period for the Midwest.

The last winter outlook issued in November, 2012 had called for near average temperatures (warm December, warm January and near average February) and for above average precipitation for the southern half of Missouri and the southern quarter of Illinois with near average precipitation elsewhere.  Kansas City finished meteorological winter 2.5 degrees above average while St. Louis finished 3.5 degrees above average. Precipitation (rain and snow melt) came in at 0.17″ above average in Kansas City, and 0.91″ above in St. Louis. (Comparatively, the Winter of 2011-2012 finished 5.2 degrees above average in Kansas City and 5.9 degrees above average in St. Louis.) The map below shows the coldest temperatures recorded of the winter of 2012-2013.

The Midwest Regional Climate Center's map of the lowest recorded temperatures of the winter of 2012-2013. No area of KC or St. Louis reported below zero temperatures for the second year in a row. Minimum temperatures around St. Louis only dropped to between 15 and 20 and to between 10 and 15 degrees in the KC Metro area. KC international, the official KC site is 20 miles NW of the city and records temperatures 5 to 10 degrees above zero at the coldest.

The Midwest Regional Climate Center’s map of the lowest recorded temperatures of the winter of 2012-2013. No area of KC or St. Louis reported below zero temperatures for the second year in a row. Minimum temperatures around St. Louis only dropped to between 15 and 20 and to between 10 and 15 degrees in the KC Metro area. KC international, the official KC site is 20 miles NW of the city and records temperatures 5 to 10 degrees above zero at the coldest.

It is for this reason that even if a winter outlook is issued calling for above average temperatures, don’t automatically equate that with little or no snow. It only takes a quick and perhaps even temporary pattern change to make a non-winter a winter to remember.

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