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  • Tim McGill

A Meltdown This Week

The Melting Follows The Misery

We will say sayonara to most of our thick blanket of snow this week. We are looking at a streak of at least eight straight days (including yesterday) where high temperatures are expected to be above freezing. There is very little if any precipitation expected during this period. It will be a welcome break coming on the heels of a couple of weeks that featured some of the worst winter weather we have endured in a long time. The meltdown will hopefully be gradual enough to avoid any serious flooding.

The Accumulated Winter Season Severity Index (AWSSI) keeps a running tally on just how extreme a winter a certain location is having. It is more commonly known as the "misery index". The categories it uses to rank winters from the least miserable to the most include "mild", "moderate", "average", "severe" and "extreme". We went from a "mild" winter at the start of February to a "severe" winter within just a couple of weeks. It was a dramatic turn for the worse. The three week period from January 26th through February 15th saw the most snowfall at O'Hare of any three week period since 1979. 21.6" of snow has fallen in February making it the 9th snowiest on record. Snow isn't the only thing that makes a winter miserable. Cold contributes to our pain too. We have had a lot of that lately as well. February is running about 13° below average. It is the biggest drop from average for a month for at least the last five years. If February ended today it would enter the history books as the coldest on record.

Accumulated Winter Season Severity Index

Yesterday was the 17th straight day with below average temperatures. A new streak starts today. Highs should be above freezing today and all the way through the weekend. Today's highs should top out in the middle to upper 30s. Average highs for today's date are around 38°. Gusty southwest winds will make it feel like the 20s most of the day.

The hourly temperature meteogram for O'Hare shows our warmer pattern hanging around through the weekend. Tuesday's highs will be the warmest in nearly two months. Notice the dramatic drop Sunday night into Monday. A quick shot of colder air could be coming and some snow may precede it. More on that below.

The temperature anomaly forecast has temperatures by Wednesday morning nearly 10° above average. No hints of Arctic air on the map. The Rockies and the Pacific Northwest will be around 4° to 14° below average but no signs of bitter cold like we experienced earlier in February.

Snow Free Through Saturday

The latest GFS model's meteogram shows a chance for plain old rain on Saturday but no snow in the forecast until late Sunday into Monday. That system is a long way off and the forecast is subject to change.

The accumulated snowfall meteogram for O'Hare shows the range of snowfall predictions from several models. The snowfall late Sunday into Monday could be as little as a dusting to as much as nearly a half a foot. I expect those numbers to change as we get closer to the event so keep the shovel in the garage for now.

The GFS model total snowfall accumulation through next Monday morning spits out around four to eight inches late Sunday into Monday morning. This includes little more than an inch of snow that fell last night in our northern suburbs. Still a very early outlook so stay tuned for changes and revisions to this.

Out Of The Deep Freeze?

The longer range temperature probability forecasts suggest we return to near normal temperatures overall for the end of February and the start of March. Average highs for this period are around 40°. As I mentioned in an earlier post, this winter has been anything but average. We started off with December 5.1° above average. January was a bit warmer coming in at 5.4° above average. February is now running nearly 13° below average. The latest 6-10 day temperature probability forecast has the Chicago area outlooked for around average temperatures overall from February 27th through March 3rd. The longer range 8-14 day forecast continues to keep us outlooked for about average temperatures overall from March 1st through March 7th too.

The even longer range Subseasonal Experiment (SubX) forecast shows a shift from a bit colder than average pattern to a pattern favoring around or just a bit above average temperatures. The forecast for the week ending March 12th keeps us slightly colder than average overall but northern Illinois returns to near normal or slightly above for the following week ending on March 19th.

Active Weather Pattern May Linger Into March

The long range precipitation probability forecasts again suggest an active pattern for the end of February through the start of March. The 6-10 day forecast favors us for above average precipitation overall from February 27th through February March 3rd. The longer range 8-14 day forecast has us outlooked for above average precipitation overall from March 1st through March 7th too. Average high temperatures will be climbing into the lower 40s for these periods and the long range temperature forecasts discussed above keep us overall around average so much of this precipitation could be coming in the form of rain.

Here is my 7 day forecast:

Today: Mostly cloudy, blustery High: 38

Tuesday: Partly to mostly sunny Low: 32 High: 43

Wednesday: Partly to mostly cloudy Low: 32 High: 38

Thursday: Partly to mostly sunny Low: 23 High: 36

Friday: Partly to mostly sunny Low: 18 High: 38

Saturday: Chance of rain mainly early, mostly cloudy Low: 32 High: 41

Sunday: Partly to mostly cloudy, snow possible late Low: 30 High: 39



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