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  • Tim McGill

Bracing For Round Two

Updated: Dec 31, 2020

Another Messy Mix Coming

The nearly three inches of snow on Tuesday helped to reduce the snowfall deficit some for this season. The 2.6" of snow that fell means we are now a bit over five inches below average for snowfall this winter so far. We could make up more of that deficit on New Year's Day as another complicated system impacts the Chicago area.

Here is a summary of the snowfall we saw with our first system of the week.

Today will be the calm before the second storm of the week. Clouds today should break for some sun at times. Look for highs to be about or just a bit below average as temperatures top out around 30°. Lower 30s are possible south of the city and highs might not climb out of the upper 20s in areas north and west of the city where more snow is on the ground.

It's hard to get snow when temperatures are above freezing. Tomorrow's temperatures will be critical in determining the amount of sleet, freezing rain, rain and snow we get. Highs should be near or just above freezing. After New Year's Day our highs will mostly be above freezing through next Thursday. I discuss the longer range temperature outlook below and it continues a relatively mild pattern well into the new year. Tomorrow's system might be the last good chance of snow for the next several days.

The GFS model's precipitation meteogram shows two systems to impact us over the next ten days. The first is Friday with a mix of sleet, freezing rain and snow changing to snow then then back to rain or a mix of rain and snow Friday night. The next system should be mainly rain late Wednesday into early Thursday.

The heaviest amount of icing from freezing rain and sleet will probably hit areas well south and west of the city that are now under a winter storm watch (in blue) is posted for Friday. Two to four tenths of an inch of ice are possible there. Winter weather advisories (in purple) for most of the area where up to two tenths of an inch of ice are possible along with up to three inches of snow.

Snowfall Forecast

The GFS model lays down about two to three inches of snow with tomorrow's system for most areas north of I-88. It hints at possibly up to four inches along the Wisconsin border in parts of Lake and McHenry county. This model has snow ending early Saturday morning.

The meteogram for O'Hare displays several different model forecasts for snowfall. The range is from as little as around a half inch to as much as six inches of snowfall in total.

The European model has higher amounts of snowfall because it brings additional snow late Saturday night into Sunday. It is showing most of the area getting about five to six inches of snow. I'm favoring the GFS model for snowfall but this is a complex system where a slight change in the track or a bump of a degree or two above or below freezing can make a big difference in the amount and type of precipitation we end up getting.

Icing will have the greatest impact with this storm. The GFS model is spitting out anywhere between about a tenth of an inch north of the city to about two tenths in the city and up to four tenths well south of the city.

Strong Signal For "Mild" Pattern

The longer range temperature probabilities continue to favor us for above average temperatures into the middle of next year. The signal has gotten stronger with higher probabilities of us being relatively mild. The 6-10 day temperature probability forecast has the most of the country outlooked for average temperatures overall from January 4th through January 8th. The longer range 8-14 day forecast continues to favor us for above average temperatures overall during the period from January 6th through January 12th. Notice the highest probabilities for above average temperatures are centered around the Great Lakes.

"Mild" Stretch Well Into January?

December will end up as the 10th month this year to have temperatures overall above average. The experimental multi-model ensemble temperature anomaly forecast suggests January may also end up above average too. The forecasts for both the week ending on January 15th and the week ending on January 22nd both have us outlooked for above average temperatures overall.

More Active Longer Range Pattern

Our two messy systems this week marks a change towards a more active pattern. The trend in the longer range precipitation forecasts continues this trend and favors us for above average precipitation overall. The 6-10 day forecast from January 4th through January 8th has us outlooked for above average precipitation. The 8-14 day forecast from January 6th through the 12th also has us outlooked for above average precipitation overall too with slightly higher probabilities. This along with the temperature probability forecasts would suggest upcoming systems might more likely feature of a mix of precipitation or even contain just rain.

Here is my 7 day forecast:

Winter Weather Advisory From 10 AM Friday To Midnight Friday Night (most areas)

Winter Storm Warning From 6 AM Friday To Midnight Friday Night (southwest of the city)

Today: Becoming partly cloudy High: 31

New Year's Day: Wintry mix early then rain and snow by the evening Low: 26 High: 36

Saturday: Partly to mostly cloudy Low: 29 High: 38

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

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

Tuesday: Partly to mostly sunny Low: 28 High: 39

Wednesday: Mostly cloudy, light rain late Low: 29 High: 42



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