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  • Tim McGill

Forecast Has At Least A Few Flakes

Coldest Temps Since February

Monday's high of 32° was the coldest in nearly ten months. This morning O'Hare dipped into the teens for the first time since February. We started off the day with wind chills in the single digits.

Today will still be chilly with highs again in the lower 30s. Wind chills during the afternoon will be in the teens and twenties.

We will begin to thaw out after Thursday. Highs Friday, Saturday and Sunday should be closer to 40°. Monday will be milder with highs in the lower to middle 40s.

Some Shots At Snow

There are at least three chances for snow between now and Christmas day. There could be a few flurries today then the most promising chance of snow is later Wednesday into Thursday morning. Later Saturday into Sunday there could be a mix of rain and snow and beyond that there is a chance for some light snow or a mix next Tuesday.

The GFS model is hinting at a more active pattern but none of these events looks to be big snow makers.

The models have a range of just a tenth of an inch of snow to nearly an inch for Wednesday's system. The other systems from this vantage point would squeeze out even less snow than that.

Breaking Down The Models

I'm going to focus on Wednesday's system and look at three different model's solutions for snowfall.

The latest GFS model run suggests a few tenths of an inch for our western suburbs but up to nearly an inch in and around the city.

The European model offers similar snowfall amounts but distributes it differently. It suggests nearly an inch in our northern and northwestern suburbs and a few tenths of an inch in Chicago.

The NAM model has a few tenths of an inch north and west of Chicago and around a half inch or a bit more from the city southward.

Based on those three models it seems safe to say the range of snowfall Wednesday into early Thursday will be from a few tenths of an inch to around an inch. The storm track with this system is south of the city so I think the south suburbs are favored for the higher end of that range. Lake effect will also be a factor so the city itself could see at least a half inch or even more.

It's About Time

We have seen just .7" of snow so far this season which is nearly 4 inches below average. Since October there have been seven days with snowfall reported at O'Hare but six of those saw just a trace.

The graphic below best illustrates our "snow drought". Most of Oklahoma has seen more snowfall-to-date than we have seen in Chicago.

As I mentioned in yesterday's post, there is a trend we have been seeing that might explain at least in part, this lack of early season snowfall.

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.

Strong Signal For Mild End To Month

Hard to get snow when you are above freezing. The long range temperature probabilities forecasts keep us above average for the week of Christmas and beyond. The 6-10 day temperature probability forecast has the highest probabilities of us being above average overall. It covers the period from December 20th through December 24th. The longer range 8-14 day forecast keeps us outlooked for above average temperatures overall from December 22nd through the 28th.

I shared this yesterday and wanted to include it in today's post because it has been rare lately to see the longer range experimental multi-model ensemble to have us outlooked around average. It shifts the area with probabilities of above average temperatures overall 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.

Trending Towards Less Precipitation

The longer range precipitation probabilities forecasts continue to trend us towards a drier forecast as December comes to an end. The 6-10 day forecast from December 20th through December 24th has us outlooked for about average precipitation overall. The 8-14 day forecast from December 22nd through December 28th has the area outlooked for below average precipitation overall in the middle of the country growing and expanding into the western part of Illinois.

Here is my 7 day forecast:

Today: Mostly cloudy, few flurries possible, a bit breezy High: 34

Wednesday: Mostly cloudy, flurries or light snow Low: 27 High: 36

Thursday: Partly to mostly cloudy Low: 28 High: 37

Friday: Partly to mostly cloudy Low: 26 High: 41

Saturday: Cloudy, light rain or snow possible Low: 34 High: 40

Sunday: Partly to mostly cloudy Low: 29 High: 40

Monday: Partly to mostly sunny Low: 30 High: 43



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