By Meteorologist Tom Skilling
The latest outbreak of arctic air tightens its grip on the Chicago area Thursday. This latest vestige of winter weather is but the beginning of a spell of challenging weather here. In addition to the chill, the season's heaviest snowfall appears to be targeting the region Friday and Friday night.
There's no question past Januarys have slammed the area with significantly colder temperatures than those predicted Thursday. It's also true cold spells in the past have lingered for days on end, unlike this one which is expected to hit then pull back. Still, the prospect of temperatures falling into the 8 to 14-degree range Thursday afternoon amid single digit and even sub-zero wind chills in a winter as meek as this one, isn't likely to go unnoticed. After all, winter 2011-12 has been running nearly 12-degrees to date milder than a year ago.
Northern Minnesota bearing the cold's brunt with 30 to 40-below morning wind chills
This winter's unusual "warmth" hasn't been limited to Chicago. The sub-zero temperatures which finally arrived in Minneapolis overnight---the first there this season--- tied with 1889 and 2002 as the Twin Cities' latest-occurring sub-zero readings.
Combined with Thursday morning's gusty northwest winds, some northern Minnesota wind chills are predicted to fall to 30 to 40-degrees below zero.
Chilly as it will feel in Chicago, the absence of a deep snowpack in this part of the Midwest is likely to spare the city the type of intensely cold temperatures which might otherwise occur with a cold outbreak of Thursday's strength.
Snowstorm threatening Friday and Friday night; system could lay down the 2011-12 winter season's biggest snow to date
That the second snowstorm in just over a week---one capable of heavier accumulations than the 4.9 inch tally recorded at O'Hare last Thursday---is on the way, is likely to prove a bigger weather story than Thursday's brief but intense chill. If trends continue, sections of the metro area may be on the way to 4 to 8 inch accumulations between the onset of snow mid-Friday morning and its exit late Friday night. In a few locations, even more snow may fall.
There are indications lake-effect flurries may persist beyond the storm system's main snows---though the bulk of the accumulation appears likely to occur between later Friday morning and just past midnight Friday night/Saturday morning.
All the ingredients for a 4 to 8 inch accumulation appear in place; Gulf's "wide open", jet stream wind maxima to help produce "lift" to generate snow
Atmospheric conditions must mesh perfectly to produce a snow of Friday's magnitude---and the forecast scenarios being put forth by virtually all computer models in the past several days fall in that category.
The Gulf is "wide-open", sending an uninhibited flow of moisture north into the Midwest, where two bands of strong jet-stream levels winds are predicted to "couple" (combine), lifting and cooling the moist air. This process is to saturate the atmosphere Friday, producing clouds and precipitation. What's more, the northbound flow of mild, moist air is to be vigorously cooled as it encounters the arctic chill here.
Forecast models from the U.S., Canada and Europe have all converged in recent days on the same solution, each placing Chicago in or near the corridor of maximum snowfall. If this line of reasoning holds up---and we'll continue monitoring developments up to the onset of snowfall Friday---then travel will become challenging by lunchtime Friday and for the day's evening rush hour.
The latest outbreak of arctic air tightens its grip on the Chicago area Thursday. This latest vestige of winter weather is but the beginning of a spell of challenging weather here. In addition to the chill, the season's heaviest snowfall appears to be targeting the region Friday and Friday night.
There's no question past Januarys have slammed the area with significantly colder temperatures than those predicted Thursday. It's also true cold spells in the past have lingered for days on end, unlike this one which is expected to hit then pull back. Still, the prospect of temperatures falling into the 8 to 14-degree range Thursday afternoon amid single digit and even sub-zero wind chills in a winter as meek as this one, isn't likely to go unnoticed. After all, winter 2011-12 has been running nearly 12-degrees to date milder than a year ago.
Northern Minnesota bearing the cold's brunt with 30 to 40-below morning wind chills
This winter's unusual "warmth" hasn't been limited to Chicago. The sub-zero temperatures which finally arrived in Minneapolis overnight---the first there this season--- tied with 1889 and 2002 as the Twin Cities' latest-occurring sub-zero readings.
Combined with Thursday morning's gusty northwest winds, some northern Minnesota wind chills are predicted to fall to 30 to 40-degrees below zero.
Chilly as it will feel in Chicago, the absence of a deep snowpack in this part of the Midwest is likely to spare the city the type of intensely cold temperatures which might otherwise occur with a cold outbreak of Thursday's strength.
Snowstorm threatening Friday and Friday night; system could lay down the 2011-12 winter season's biggest snow to date
That the second snowstorm in just over a week---one capable of heavier accumulations than the 4.9 inch tally recorded at O'Hare last Thursday---is on the way, is likely to prove a bigger weather story than Thursday's brief but intense chill. If trends continue, sections of the metro area may be on the way to 4 to 8 inch accumulations between the onset of snow mid-Friday morning and its exit late Friday night. In a few locations, even more snow may fall.
There are indications lake-effect flurries may persist beyond the storm system's main snows---though the bulk of the accumulation appears likely to occur between later Friday morning and just past midnight Friday night/Saturday morning.
All the ingredients for a 4 to 8 inch accumulation appear in place; Gulf's "wide open", jet stream wind maxima to help produce "lift" to generate snow
Atmospheric conditions must mesh perfectly to produce a snow of Friday's magnitude---and the forecast scenarios being put forth by virtually all computer models in the past several days fall in that category.
The Gulf is "wide-open", sending an uninhibited flow of moisture north into the Midwest, where two bands of strong jet-stream levels winds are predicted to "couple" (combine), lifting and cooling the moist air. This process is to saturate the atmosphere Friday, producing clouds and precipitation. What's more, the northbound flow of mild, moist air is to be vigorously cooled as it encounters the arctic chill here.
Forecast models from the U.S., Canada and Europe have all converged in recent days on the same solution, each placing Chicago in or near the corridor of maximum snowfall. If this line of reasoning holds up---and we'll continue monitoring developments up to the onset of snowfall Friday---then travel will become challenging by lunchtime Friday and for the day's evening rush hour.
