AmyFreeze's Blog

AMY FREEZE

WINTER FORECAST 2008-2009

Just like clockwork, on the first meteorological day of winter, Chicagoland got blanketed with snow. 

During the past several weeks, cold air has arrived from Canada, and we have already been clipped with a few surges of sub freezing air. But is this early season cold and snow is likely a sign of the winter ahead. 

Last winter had a mild start.. but a cold finish.  The winter months last year were active with small but potent storms delivering 60" of annual snowfall at O'Hare.  This winter, the science suggests that another cold, wet winter lies ahead.  I looked at:    sea surface temperatures, seasonal trends and prevailing storm patterns to create this forecast. 

First, sea surface temperatures in the Pacific Ocean... these patterns are valuable for long-range forecasting.  For example, La Nina, colder than normal ocean temperatures,  had a big impact on last winter and our summer weather--  but La Nina is turning into la nada... the ocean temperatures that give us clues to the winter are forecast to disappear -- which makes this winter's forecast exceptionally challenging.  

I looked for similar years to what's happening now ---  where the la nina was strong then faded.    these were years coming off la nina into a neutral winter                               25.5  average temp   28"average snow

1950-1951             23.5      40.1"

1985-1986              21.3     23"

1989-1990              27.5     22"

1996-1997             25.3      35.8"

These examples tended to produce colder than normal temperatures but the snow amounts were highly variable to 22" one year, more than 40"  in another.  

Next, i turned to recent climate patterns --- the SEASONAL TRENDS... because current research (Journal of Climate) shows that the previous seasons give clues for winter weather ahead.  Last winter and this summer in Chicago both had near normal temperatures and both were wetter than average. This autumn both october and november were colder than average...  but both were also below average for precipitation... October    -.5  degrees below average,  -.64" in average rainfall.  November was  -.2 degrees below average and -1.7" in rainfall. 

The final piece of science suggests snow is coming.  The evidence is found in the prevailing storm patterns.  Current storm patterns suggest the jet stream is shifting to where the boundary between cold air to the north and warm air to the south will be right over chicago. 

This is an ideal set up for active Winter.  It's a pattern brings storms out of Canada and drags them over chicago--- we call them "Clippers" because they bring quick doses of snow --- but these events will also re-enforce the Cold Air intrusion across the Midwest.

My call for this winter is Cold and Wet.

25.5 degrees is average temperature in Chicago for Dec thru Feb 

My forecast:  21 to 23 degrees with December being the coldest, January the most mild.

28" of snow is the average snowfall for Chicago Dec. thru Feb.  It won't be as snowy as last winter but my forecast is above average snowfall: 32 to 38 inches

Finally - it's not an official disclaimer but it's something important to note.  The confidence is not as high in this winter forecast because there are no definitive long term controlling patterns like a La Nina. But the average date of 1" or more of accumulating snow in Chicago is december 4th... we've already hit that mark early and a bitter chill is coming our way this week.

Another new piece of information is the ocean pattern called the NAO -which is best suited for short term forecasting -- suggests a harsh, active mid December... so a cold snow storm for our region in mid December wouldn't be a surprise.

Click here to compare my forecast to Climate Predication Center's Winter Outlook!