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  • Tim McGill

Snow First Then Dramatic Drop In Temperatures

The Calm Before The One-Two Punch

A break today from both bitter cold and snow. It will be a brief break because a one-two punch of snow followed by a bitter blast of Arctic air is just around the corner. The snow arrives later Thursday and then the dramatic drop in temperatures comes Thursday night into Friday. It could be accompanied by a flash freeze and near white-out conditions. Winter storm watches beginning tomorrow are posted as close as Rockford with winter weather advisories as close as Kenosha. Advisories or watches may be needed here so stay tuned.

Some sunshine today will me mixed with clouds. That sunshine and a southwest breeze will help push our highs to near 30°. There may be some areas of freezing fog early today mainly west of the city.

Thursday will be the warmest day we see probably through all of next week. Our highs tomorrow should be near 40°. The models in the hourly temperature meteogram below have lows by Sunday morning dropping to near -20°. So with the wind chill taken into consideration it will feel nearly 70° colder by then compared to tomorrow afternoon. Sub-zero lows are possible Saturday morning and Monday morning too.

The latest GFS model model once again has lows plummeting to 15° to 25° below zero Sunday morning. The record low for Sunday is -10°. If this model verifies it would shatter a record that goes back 146 years. Wind chills could be as cold as -30° to -50°. I suspect the model might ease up by at least a few degrees as we get closer to the weekend but the record would still be in jeopardy. The last time we dropped below -10° was more than four years ago. The last time we dropped to -15° or colder was nearly seven years ago.

The temperature anomaly forecast for Sunday morning has the core of the Arctic air stretching from Minnesota southward into northern Illinois. Temperatures here will be 30° to 40° or more below average.

Sunday morning could be book ended by sub-zero lows Saturday morning and Monday morning. The GFS model has lows Saturday morning around -3° to -7°. Monday morning's lows are forecast to drop to -8° to -20°. These numbers may also change in the coming days but the main message hasn't changed and that is we will be experiencing the coldest air of the season so far. It could be the coldest air we have seen in at least a few years.

Saturday morning's forecast temperatures (left). Monday morning's forecast temperatures (right)

Snow First Before Frigid Air Arrives

The GFS model cloud cover and precipitation meteogram has snow developing Thursday afternoon. There will be some rain and possibly a wintry mix especially along and south of I- 88. The Arctic front comes through Thursday night with gusty winds that could cause some blowing and drifting snow and reduce visibilities to near zero.

GFS Model Cloud Cover & Precipitation Meteogram For O'Hare

The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. Thursday's snowfall range is anywhere between a half inch to about 5.5" of snow. More on the snowfall forecast below.

Snow Surplus To Grow

The GFS model squeezes out four to six inches of new snow here late Thursday into early Friday for most of us. Higher amounts up to nearly 8" are shown for spots well west of the city and lighter amounts south where it is more likely rain or a mix will fall. This would push our snow surplus even higher than it already is. So far this winter we have picked up 24.7" of snow which is 5" above average.

The European model lays down less snowfall in its forecast. It spits out about around three inches in the city and points south and three to four to five inches north and west of Chicago.

The Winter Blues

The cold air that comes crashing in by the end of the week might linger here through the middle of the month. A lot of blue on the long range temperature probability forecasts and the shades are getting darker. The blue represents areas outlooked to be below average overall during the period. As I mentioned yesterday, some of the darkest shades of blue which indicate the higher probabilities are centered near or over Chicago. They are a shade darker today compared to yesterday. The latest 6-10 day temperature probability forecast has the Chicago area outlooked for below average temperatures overall from February 8th through February 12th. The longer range 8-14 day forecast continues to keep us outlooked for below average temperatures overall from February 10th through February 16th.

The even longer range Subseasonal Experiment (SubX) forecast seems to suggest February will stay frigid (overall) through nearly the end of the month. The forecasts for both the week ending February 19th and the week ending February 26th have us favored for below average temperatures overall.

Pattern To Become Less Active?

Our recent active pattern may settle down by the middle of the month. The 6-10 day forecast favors us for below average precipitation overall from February 8th through February 12th. The 8-14 day forecast keeps us outlooked for below average precipitation overall from February 10th through February 16th.

Here is my 7 day forecast:

Today: Partly to mostly sunny High: 32

Thursday: Rain or wintry mix changing to snow, blustery Low: 27 High: 38

Friday: A.M. flurries, partly to mostly cloudy, patchy blowing/drifting snow Low: 10 High: 16

(Total accumulations by early Friday around 2 to 5 inches with the heavier end of that range north and west of the city. Around and inch or two south of the city.)

Saturday: Mostly cloudy, light snow possible Low: 2 High: 14

Sunday: Mostly cloudy, very cold Low: -10 High: 7

Monday: Partly to mostly sunny Low: -8 High: 12

Tuesday: Partly to mostly sunny Low: -1 High: 15



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