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  • Tim McGill

Keep The Shovel Handy

A Taste Of Spring First


Yesterday's 36° high was the third straight day with highs in the 30s. It was the coldest three day stretch we have seen in a little over ten months. It stands out because we had been rather mild for the past few weeks. These past three days were actually right around average. In the past twenty-one days there has only been one day below average. December is now running around 4° above average.


This morning clouds broke for some sunshine. That sunshine will help us thaw out on this Wednesday. Highs will climb back above average again. Look for highs today in the upper 40s and even warmer weather tomorrow.



Thursday will be the warmest day we'll see for at least the next seven days or so. Highs tomorrow should climb to 50° or above. More sunshine and a southerly wind will help make it feel more like spring than early winter. Expect 40s for highs on Friday. 40s are expected early on Saturday but temperatures will tumble into the 30s in the afternoon. Some of the coldest air of the season so far (by a degree or two) will arrive late in the weekend and linger into early next week. This next round of cold is still expected to be right around average for the middle of December.


I am very impressed with the GFS model temperature anomaly forecast for Thursday. From Texas to Minnesota temperatures will be around 15° to 25° above average. Our temperatures could be nearly 20° above average tomorrow. That would mean highs in at least the lower 50s. It will feel more like late March or early April than December.


Some Sticking Snow Saturday


I am not complaining but our snowfall deficit grew a bit more yesterday. We are now a little over three inches below average. We could make up that amount and then some with a weekend storm that might lay down heavy snow in portions of northern Illinois. The GFS model has rain developing late Friday and into Saturday. The change to snow could begin first Friday night near the Wisconsin border and continue during the day Saturday as temperatures fall from the 40s into the 30s. Most of the snow would fall Saturday afternoon into Saturday night.



The accumulated snowfall meteogram for O'Hare shows several models solutions for Saturday's snow. Some models suggest as little as a half of an inch while other suggest up to more than eight inches possible.


There was a much great disparity between models yesterday regarding our weekend storm. The GFS model and the European model are showing more agreement in their latest runs.


The GFS model lays down the heaviest swath of snow from north central Illinois to northern lower Michigan. It suggests about 6 to 10 inches for our northern and northwestern suburbs and with amounts dropping sharply south and east of there. It squeezes out about an inch of snow for the city.


The European model is laying down the heaviest snow just a bit further south and east. It suggests about 7 to 8 inches from the city north and westward. The only areas spared this heavy snow would be far southern suburbs and northern Indiana.



I still caution that we are at least a few days away from this event and a lot could change. The different parts of this storm are still well west of here and there will be adjustments to these snowfall forecasts. It does look pretty clear though that parts of the Midwest will see several inches of snow on Saturday.


Strong north and northeasterly winds will develop with this storm Friday night into Saturday. These winds could whip up waves up to 8 feet high on the southern end of Lake Michigan and cause some lakeshore flooding. The worst of this would be late Saturday afternoon into Saturday night.



Cold Doesn't Last Long


In the wake of the weekend storm we will have a couple of colder days but long range forecasts hint this won't last long. The 6-10 day temperature probability forecast has us outlooked for about average temperatures overall from December 14th through December 18th. The longer range 8-14 day forecast from December 16th through the 22nd outlooked to return to above average temperatures overall.



The even longer range experimental multi-model ensemble has us outlooked for above average temperatures overall through both the week ending on Christmas day and the week ending on New Year's Day. The area of orange and red that represents temperatures at least 1° to 5° or more above average grows bigger and moves more over the Midwest during this two week period.





Precipitation Pattern Change


When I shared yesterday's long range precipitation probabilities forecasts they both had us outlooked for above average precipitation overall. That has now changed. The 6-10 day forecast from December 14th through December 18th has us slightly favored for below average precipitation overall. The 8-14 day forecast from December 16th through December 22nd has outlooked for below average precipitation overall too.




Here is my 7 day forecast:


Today: Partly to mostly sunny High: 49


Thursday: Mostly sunny Low: 32 High: 52


Friday: Mostly cloudy, light rain late Low: 37 High: 46


Saturday: Rain mixing with/changing to snow Low: 37 High: 43 (falling into the 30s pm)

Sunday: Partly to mostly sunny Low: 28 High: 37

Monday: Partly to mostly sunny Low: 24 High: 35


Thursday: Partly to mostly sunny Low: 25 High: 35


#ilwx

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