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  • Tim McGill

Setting My Sights On Saturday's Snow

From Spring To Winter in Less Than 48 Hours

It's been a relatively mild month of December so far. Yesterday's 53° high was 17° above average. Rockford actually set a record high yesterday topping out at 55°. At O'Hare the month is now running 5.1° above average. This mild pattern goes back to November. That month was an incredible 7.1° above average.

Today's highs will be nearly 20° above average in some spots. Look for highs today in the lower to middle 50s. Those are typical temperatures for late March or early April! Plenty of sunshine and a southerly breeze will help make it feel like spring.

Today will be the warmest day of at least the next seven. Friday's highs will be in the middle 40s and we will start off in the lower 40s early Saturday before falling into the 30s during the afternoon. While the drop in temperatures may be dramatic, we are only falling back to about average for Sunday and early next week with highs in the lower to middle 30s.

The GFS model temperature anomaly forecast for today looks like it is on fire. Most of the country will be mild for December with the Midwest and Missouri Valley seeing the biggest jumps from normal. Highs there will be between 20° to 25° above average.

Grab The Shovel Or Just A Scraper?

We are now 3.1 inches below average on snowfall going back to the start of November. At the very least we will put a dent in that deficit this weekend. The GFS model continues to develop rain here late Friday and into Saturday. The change to snow for most areas will be during the afternoon Saturday but near the Wisconsin border that change could occur as early as late Friday or early Saturday morning. The snow should wrap up by late Saturday night or early Sunday morning.

The accumulated snowfall meteogram for O'Hare has a wide range of solutions for Saturday's snowfall. On the low end some models have as little as a half inch and on the high end at least one model is suggesting over five inches.

The European model has nudged the Saturday's storm track a bit further north compared to the GFS model.

The latest GFS model run has brought more significant snow further south and southeast. It actually has the highest snowfall totals from the north side of the city along the lakeshore northward through Lake county and Kenosha county Wisconsin. It squeezes out about six to ten inches of snow there. Outside of those areas the snowfall amounts vary from about two to four inches for most areas.

The European model paints the heaviest swath of snow here in our far northern and northwestern suburbs with six to ten inches of snow common there. The south suburbs and city is spared with a half inch of snow or less.

Like yesterday, I continue to caution that we are at least a few days away from this event and a lot could change. I am leaning towards a bit more rain initially with this system than the GFS model suggests. This would cut back the snowfall totals quite a bit in and around the city. I still think the far northern and northwestern suburbs have the best chance of seeing significant snow on the order of five to ten inches.

Dreaming Of A White Christmas?

The National Weather Service has an interactive map of the U.S. that will show the probability of a white Christmas for a place just by clicking on it. It is based on the latest (1981-2010) U.S. Climate Normals from NOAA's National Centers for Environmental Information (NCEI).

This probability is based on past climatological records for O'Hare. This suggests the probability of O'Hare having a white Christmas is 37%. As stockbrokers will tell you "past performance doesn't guarantee future results". We could end up having a white Christmas for the next ten years in a row or go without any snow on Christmas day for the next ten. Probability is the chance that something will happen or put another way, the probability of an event is a measure of the likelihood that the event will occur.

While the map shows the historical probability that a snow depth of at least one inch will be observed on December 25, the actual conditions in any year may vary widely from these because the weather patterns present will determine the snow on the ground or snowfall on Christmas day. These probabilities are useful as a guide only to show where snow on the ground is more likely.

Here is the wide range of possibilities for a white Christmas in our area from least to greatest:

Kankakee 34%

Elgin 35%

Crystal Lake 39%

Midway Airport 41%

Antioch 42%

Harvard 46%

DeKalb 49%

Rockford 55%

Winds To Whip Up Big Waves

One thing hasn't change for Saturday's storm. Strong north and northeasterly winds are still expected to develop with this storm Friday night into Saturday. These winds could whip up waves up to 10 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.

Back Above Average Christmas Week

After some seasonably chilly weather next week it appears we will bounce back fairly quickly. The 6-10 day temperature probability forecast has us outlooked for about average temperatures overall from December 15th through December 19th. The longer range 8-14 day forecast from December 17th through the 23rd outlooked to return to above average temperatures overall.

Long Range Precip Pattern Up In The Air

The longer range precipitation probabilities forecasts trend us towards higher than average precipitation over the next couple of weeks. The 6-10 day forecast from December 15th through December 19th has us outlooked for about average precipitation overall. The 8-14 day forecast from December 17th through December 23rd has outlooked for above average precipitation overall but it isn't a very strong signal.

Northern Lights This Far South?

There may be a window where skies are clear enough this evening and early tonight to catch a rare glimpse of the Northern Lights. The sun will send a geomagnetic storm some 93 million miles and when it interacts with the highest levels of our atmosphere the results could be breathtaking.

According to the University of Alaska Geophysical Institute aurora activity will be high.

Weather permitting, highly active auroral displays will be visible overhead from Inuvik, Yellowknife, Rankin and Iqaluit, to Portland OR, Cheyenne, Lincoln, Springfield, and New York City, and visible low on the horizon as far south as Carson City, Oklahoma City, and Raleigh.

Here is my 7 day forecast:

Today: Mostly sunny & mild High: 55

Friday: Mostly cloudy, rain develops pm, becoming breezy Low: 37 High: 46

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

Sunday: Partly to mostly cloudy Low: 27 High: 36

Monday: Partly to mostly sunny Low: 25 High: 37

Tuesday: Partly to mostly sunny Low: 27 High: 38

Wednesday: Chance of light snow, mostly cloudy Low: 28 High: 36



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