Finally Cold Enough For Snow But Not Much In The Forecast
Timing Is Everything
Cold days have been rare going back to the start of November. We have only seen seven days with below average temperatures since November 1st. We finally have a few days in a row with below average temperatures in the forecast but unfortunately for snow lovers, there isn't much moisture around for snow to form. Today should be the coldest day of the season so far and coldest in over ten months. Tonight will probably be the coldest night of the season so far too.
Look for a brisk northwest wind to deliver some cold air here on this Monday. Highs today will barely get up to 30°.
Highs should be in the 30s right through Thursday. We will warm up just a bit by the weekend with highs near 40°. This will be the coldest week in just over ten months.
Today's chilly temps will combine with a brisk breeze to drop wind chills into the teens. They will stay in the teens until midday tomorrow.
Cold But Quiet Pattern
We are now nearly four inches below average on snowfall going back to the start of November.
The GFS model keeps us relatively quiet for the next ten days or so. There is a system that my give us a glancing blow early Wednesday but the snowfall would be light and stay mainly south of the city. A better chance for a little light rain or snow on Saturday but little accumulation expected at this point.
Looking At Long Range Snowfall Forecasts
The latest GFS model run out through Christmas day only has a dusting for areas well west and northwest of the city.
The European model offers up a bit more snow. This model was run out through a week from Wednesday. The model spits out a few tenths of an inch in the city with up to nearly an inch in our north and northwest suburbs.
These numbers will change. I'll keep checking to see if any trends develop that would suggest a better chance for more or less snow between now and Christmas.
White Christmas Dreams Dwindling?
Our warming winters may mean the probability of us seeing a White Christmas in the future will be dropping. Looking back over the last two decades there is a trend towards increasing snowfall later in the season and a reduction of snowfall at the beginning, including the month of December. This decade has seen a 21% increase in April snowfall compared to last with a 40% decrease in December snowfall this decade compared to last. While just three of the last twenty Aprils have actually seen more snowfall than the Decembers that preceded them, two of those Aprils occurred in our last two winters.
A study by ClimateCentral.org found winter snowfall has fallen over the past fifty years in Chicago. Average annual snowfall between the decade of 1970–1979 was compared to average annual snowfall for the decade of 2010–2019. When comparing those same decades for spring snowfall the trend is decreasing sharply. However, as I mentioned above, if you compare just the average April snowfall in the decade of 2001 to 2010 with the decade from 2011 to this year, the trend is actually upward for the month.
The amount of days below below 32° in Chicago is projected to decline going forward as our climate continues to warm. This trend will also help to inhibit snowfall overall in the future.
All this would seem to suggest the future is now for seeing a White Christmas. The odds will fall and become less favorable as our temperatures rise over the coming years.
I shared some White Christmas statistics last week and want to share at least one more time.
The National Weather Service has an interactive map of the U.S. that will show the probability of a white Christmas for a place just by clicking on it. It is based on the latest (1981-2010) U.S. Climate Normals from NOAA's National Centers for Environmental Information (NCEI).
This probability is based on past climatological records for O'Hare. This suggests the probability of O'Hare having a white Christmas is 37%. As stockbrokers will tell you "past performance doesn't guarantee future results". We could end up having a white Christmas for the next ten years in a row or go without any snow on Christmas day for the next ten. Probability is the chance that something will happen or put another way, the probability of an event is a measure of the likelihood that the event will occur.
While the map shows the historical probability that a snow depth of at least one inch will be observed on December 25, the actual conditions in any year may vary widely from these because the weather patterns present will determine the snow on the ground or snowfall on Christmas day. These probabilities are useful as a guide only to show where snow on the ground is more likely.
Here is the wide range of possibilities for a white Christmas in our area from least to greatest:
Crystal Lake 39%
Midway Airport 41%
Relatively Mild End To Month
This week's cold snap is an anomaly. Until today we have had only one day below average in December. We only saw six days below average all of November. We will see three or four days in a row below average this week but the long range forecasts are signaling a return to above average temperatures overall for the end of the month. The 6-10 day temperature probability forecast has relatively high probabilities of us being above average overall from December 19th through December 23rd with. The longer range 8-14 day forecast keeps us outlooked for above average temperatures overall from December 21st through the 27th.
The even longer range experimental multi-model ensemble seems to be shifting the relatively mild air more south and east of us with time. It has us outlooked for about average temperature overall for the last week of December and the first week of January. We are sandwiched in-between the area outlooked for below average temperatures north and west of us and the area expected to be relatively mild to our east.
Drying Out For End Of The Month
The longer range precipitation probabilities forecasts trend us towards less than average precipitation by the end of the month. The 6-10 day forecast from December 19th through December 23rd has us outlooked for above average precipitation overall. The 8-14 day forecast from December 21st through December 27th has most of our area outlooked for below average precipitation overall. Since the long range temperature forecasts are above average it would appear some if not most of the precipitation coming by the end of the month would be in the form of rain.
Here is my 7 day forecast:
Today: Partly to mostly sunny High: 30
Tuesday: Mostly cloudy Low: 20 High: 34
Wednesday: Mostly cloudy, flurries or light snow possible south Low: 27 High: 35
Thursday: Partly to mostly sunny Low: 28 High: 38
Friday: Partly to mostly cloudy Low: 28 High: 41
Saturday: Cloudy, light rain and snow possible Low: 30 High: 40
Sunday: Partly to mostly clouy Low: 32 High: 42