The storm behind Thursday’s varied array of wintry Chicago weather is destined to produce a blizzard of historic proportions over the Northeast U.S. Friday and Saturday. What happens meteorologically there is likely to dwarf this system's impact on the nation's mid-section. Still, Thursday's weather here should be approached with care.
The day's icy open in Chicago, the product of rain falling into sub-freezing ground-level air, is likely to yield to rain as temperatures break above freezing by lunchtime and into the early and mid-afternoon period. The hours which follow could bring deteriorating weather conditions into the metro area.
The predicted arrival of strong cooling aloft later this afternoon is expected to take rain over to accumulating snow—a change likely to occur first within the Wisconsin border counties north of Chicago. If conditions continue to unfold as it now appears they may, the transition to snow is likely to sink southward by evening into the city and surrounding suburbs.
Model forecasts generate such strong upward vertical motion as this occurs late Thursday, the potential for embedded thunder or lightning can’t be ruled out. And it would be during this period that snowfall could become “convective”—potentially coming down in some impressive and potentially thundery bursts.
Timing of precip transition to late day snow critical to how much falls here
Precisely when the transition to snow takes place later Thursday may not only have a profound effect on the evening commute period, but also on the amount of snow which may fall. Our best estimate is 2 to 4” may accumulate, with the potential for a few heavier totals in northern counties where the transition to snow will occurs first. Amounts, as has so often happened this snow season, are likely to taper off heading south from Chicago.
Importantly, a delay in the predicted switch to snow would diminish accumulations. Forecasters will be monitoring Thursday’s weather developments carefully!
Snowfall of more than 2.6” would make Thursday’s storm this season’s heaviest yet
The heaviest snowfall of the 2012-13 season has been 2.6” and the last time 3” or more snow fell here was when 3.5” came down last February 24.
An accumulation in excess of 2.6" would become the current season's heaviest, and a total exceeding 3.5" would amount to the biggest snow to fall here in nearly a year.
Next storm to be Sunday rain-maker; active pattern to continue later next week as arctic air stages comeback
The next storm on Sunday—the sixth weather disturbance to cross the Midwest in the past two weeks—is to place Chicago in its "warm" sector, boosting the odds of rain being the favored form of precipitation.
While ice pellets may fall as the new system’s precipitation first develops Sunday morning, the transition to rain should occur expeditiously and several embedded thunderstorms aren’t out of the question.
Colder air circulates into Chicago behind the late weekend storm as Monday arrives. But markedly colder arctic air is to plunge south into much of the country later next week and into the week which follows, a development which promises a very chilly mid- and late-February period.
Two systems will be monitored as the transition to colder weather occurs—one currently projected to lift into the Ohio Valley just south of Chicago midweek and the next to take shape in the Plains during the weekend which follows.
Were either of the two systems to track into the Midwest, their snow-producing potential here could be impressive.
Storm’s explosive intensification to bring New England a historic blizzard; snowfall to be measured in feet in the hardest hit locations
The weather Thursday’s storm system produces in Chicago is to pale in comparison to the full-scale and potentially historic blizzard predicted to lambaste the Northeast U.S. Friday and Saturday.
At a number of locations, the snowfall this storm may unleash could dwarf full season tallies to date and easily qualify as this winter’s worst single storm, if not one of the most impressive winter systems to affect that region in years.
Boston and New York City could see two to three times the amount of all the snow that’s fallen to date this season
In Boston, where just 10.7” of snow has fallen to date in the 2012-13 season, 24 to 30” of snow may fall amid wind gusts approaching hurricane strength (70 mph). That would amount to a 2-day snowfall nearly three times all the snow currently on the books this season. And, estimates that a foot of snow could blanket sections of the New York City area would amount to nearly twice the amount of snow which has fallen this winter to date.