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  • Tim McGill

Chances For Sticking Snow

Thawing After Thursday

We are in fairly rare temperature territory. Today will be the fourth straight day with highs in the 30s. The last time we did that was the end of February. Yesterday's high of 34° marked the second straight day with temperatures below average. The last time we had back to back days below average was the middle of November.

Look for highs today again in the lower 30s but a brisk wind off the lake will make it feel more like the 20s most of the day.

We will see some minor snowfall accumulation in spots today and tonight but his winter so far has been a breeze. The Midwest Regional Climate Center has an index called the Accumulated Winter Season Severity Index to keep track of how severe the winter is for cities around the country. It is sometimes referred to as the "misery index". In order of severity from least to worst severe the categories are mild, moderate, average, severe and extreme. So far Chicago is in the "mild" category, the least severe of all the categories.

Nothing too miserable to be afraid of in the short term forecast. We will begin to thaw out after Thursday. Highs Friday, Saturday and Sunday should be closer to 40°. Monday and Tuesday will be milder with highs in the lower to middle 40s.

More Active Pattern

At least three systems offer a chance for some accumulating snow between today and Christmas. Today and tonight's snowfall should be light with most areas getting less than an inch of snow. Late Friday night into Saturday there could be a mix of rain and snow. Models are suggesting anything from a dusting to maybe another inch or two possible with this system. The next system after this weekend that could bring snow would arrive late Christmas Eve and continue on Christmas day. Models are not yet in agreement on this one. The GFS model lays down some heavy snow here while the European model squeezes out a dusting.

The GFS model's precipitation meteogram shows the timing for the next few systems.

The models have a range of just a tenth of an inch of snow to nearly an inch between today and tonight. The snow that falls early today is just a glancing blow from a system passing mainly to our south. We will see additional light lake effect snow late today into tonight. Saturday's system could start as a mix of rain and snow early in the morning then transition to primarily rain before ending with some light snow later in the day. The models suggest about a third of an inch to nearly two inches of snow is possible. This far out the snowfall range is pretty wide so the models are still figuring this system out and these numbers will be refined.

White Christmas More In Reach?

Before I get to the prospects for a white Christmas we need to look at today and tonight's snowfall potential.

The latest GFS model run suggests a few tenths of an inch for our western and northern suburbs but up to nearly an inch in and around the city and through northern Indiana by early Thursday morning.

The European model offers similar snowfall amounts but distributes it differently. It suggests nearly an inch in our northern Indiana but only a tenth to a few tenths of an inch in and around Chicago.

I ran out both models through Christmas afternoon to see the total snowfall accumulation possible between now and then.

The GFS model buries most of us in a half a foot of snow or more with most of that coming late Christmas Eve and on into Christmas day. The heaviest snow would be in northern and north central Indiana with some spots getting over a foot. I would be very excited about this if the European model was showing similar snowfall amounts but it isn't, at least not yet.

The European model (below) gives most of us a dusting on Christmas Eve with a bit more expected in northern Indiana.

It is still way too early to make a call about next week's system. I'll continue to update as we get closer.

Could Be A Lot Worse

One thing that is for certain is the northeast will be slammed with heavy snow late today into Thursday. More than a dozen and a half states out east have some type of winter weather advisory in effect. Nearly two feet of snow could fall in the harder hit areas.

Still Mild Signal For End Of The Month

The longer range temperature probabilities forecasts have us outlooked for above average precipitation for the end of December. The 6-10 day temperature probability forecast has the highest probabilities of us being above average overall. It covers the period from December 21st through December 25th. The longer range 8-14 day forecast keeps us outlooked for above average temperatures overall from December 23rd through the 29th but the probabilities fall just a bit. This doesn't rule out a couple of days cold enough for some snow but it suggests most days during this period will be above average.

Drying Out

The longer range precipitation probabilities forecasts has most of the Midwest drying out for the end of the month The 6-10 day forecast from December 21st through December 25th has us outlooked for below average precipitation overall. The 8-14 day forecast from December 23rd through December 29th increases the probabilities for the Chicago to see below average precipitation overall. This forecast has all of the lower 48 states either below average or about average with no part of the map showing above average precipitation for this period. I use the term "overall" because there could be a few days that actually see more precipitation than normal but the model suggests most days during the period will have below average precipitation. So the GFS model's call for significant snow around the holiday still can't be ruled out entirely.

For Winter Weather Geeks (Like Me)

Chicago's National Weather Service office hosted a winter weather preparedness and spotter training webinar last Thursday. They covered topics like winter weather science, typical winter weather in Chicago, winter weather safety and how to measure and report snowfall. Below is a link to the webinar.

Here is my 7 day forecast:

Today: Cloudy, light snow or flurries at times, a bit breezy High: 34

Thursday: Mostly cloudy, light snow showers mainly early Low: 29 High: 36

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

Saturday: Cloudy, light rain or snow possible Low: 33 High: 40

Sunday: Partly to mostly sunny Low: 28 High: 40

Monday: Partly to mostly sunny Low: 31 High: 43

Tuesday: Partly to mostly sunny Low: 34 High: 44



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