Odds Increase For A Chicago White Christmas
Mix This Morning
We finally have some wintry weather in our forecast. A light mix this morning of rain and snow early today, then possibly more significant snow early Christmas Eve day followed by the coldest air of the season so far settling in for the end of the week.
We've been spared thus far from any harsh winter weather. Only three days in December have seen temperatures below average and we are about a half a foot below average for snowfall.
Any mix we start the day off with will melt quickly with highs today expected to hit 40° or warmer for most of us. Some gusty winds will make it feel a bit colder though.
We should warm up through Wednesday when highs could flirt with 50°. The bottom drops out by Christmas Eve and the cold sticks around through Christmas day too. Wind chills by Christmas morning could be as cold as 5° to 15° below zero.
Snow Snow May Stick By Christmas
The GFS model has at least four systems with some precipitation over the next ten days. Today's is probably the weakest of the four with just a little light rain or snow early in the day. The next is late Wednesday into Christmas Eve morning with rain changing to snow. More light rain and snow possible Sunday and then another system with rain and snow a week from Wednesday.
There may be a dusting for a few of us early today but maybe more substantial snow with the following two systems. The model range for snowfall with Wednesday's system is around a half inch to an inch in total. Sunday's system has a range of a half inch to nearly two inches of snowfall.
So I'm (Still) Saying There's A Chance
The odds of seeing enough snow for a white Christmas this year have increased just a bit based on at least one computer model.
The latest GFS model is spitting out a dusting to a couple tenths of an inch of snow early on this Monday. Highs climb into the 40s today so if any snow does accumulate on grassy or elevated surfaces it will melt quickly as temperatures climb.
The GFS snowfall accumulation forecast run out through Christmas morning shows why we have hope for a White Christmas. The model lays down an inch to nearly two inches of snow mainly north and wet of the city with most of that coming early Christmas Eve morning. This scenario means a good portion of northern Illinois would see a White Christmas with the exception of the city and areas south of there.
The European model accumulated snowfall forecast for the same period squeezes out less snow. It suggests a dusting to maybe a couple tenths of an inch in total. That wouldn't be enough to make it an official White Christmas. This model has been going back and forth between light snowfall and more significant snow so stay tuned.
Fewer Future White Christmases?
According to ClimateCentral.org's study based on analysis of the 1981-2010 NOAA/NCEI climatological normals for over 240 cities Chicago has a 38% chance of a White Christmas in any given year. The whitest Christmas occurred in 1951 when there was 17" of snow on the ground.
Their report also mentions that the odds for future White Christmases will be falling. The relationship between a warming world and snowfall is complicated but their statistics on snow cover for North America shows that it is decreasing overall. One of the main reasons is that more and more winter precipitation is falling as rain instead of snow in many of the locations they looked at.
From About Average To Above
The longer range temperature probabilities are similar to so many we have seen so far this winter. The relatively mild pattern we have enjoyed(?) may continue into at least the start of 2021. The 6-10 day temperature probability forecast has us above average overall from December 26th through December 30th. The longer range 8-14 day forecast also has us outlooked for above average temperatures overall. That takes us from December 28th through January 3rd.
Above Average Start To 2021
The couple of cold days in this week's forecast look to be the exception to the above average rule we have seen so far this winter. We have only seen three days this December that were below average. Not only do the 6-10 and 8-14 day temperature probability forecasts suggest above average temperatures overall but the even longer range forecasts keep that pattern coming into the first couple wees of next year.
The experimental multi-model ensemble temperature anomaly forecast has most of the country relatively mild for the week ending January 8th. The forecast for the week ending January 15th suggests this pattern could continue through the middle of next month here in the Midwest.
Shifting Back Above Average For Precipitation
The longer range precipitation forecasts start us off drier than average but then shift us back to possibly a more active pattern. The 6-10 day forecast from December 26th through December 30th has us outlooked for below average precipitation overall. The 8-14 day forecast from December 28th through January 3rd also has us outlooked for above average precipitation overall. Neither one of these forecasts have very strong signals though.
Here is my 7 day forecast:
Today: Light rain/snow early, cloudy, blustery, pm light rain possible High: 42
Tuesday: Partly to mostly sunny Low: 30 High: 42
Wednesday: Mostly cloudy, light rain/snow developing Low: 36 High: 50
Thursday: Partly/mostly cloudy, few flurries possible High: 28 early but falling into the teens
Christmas: Partly to mostly sunny & cold Low: 7 High: 22
Saturday: Partly to mostly sunny Low: 18 High: 33
Sunday: Mostly cloudy, light rain/snow Low: 27 High: 38