Counties adjoining Lake Michigan are to deal with waves of lake-effect snowfall much of Thursday, even as their far west suburban neighbors gaze at a sun/cloud mix. The very localized nature of lake-effect snowfall is one of its hallmarks. These snows are quite selective and tend to affect just a portion of the metro area. Yet, where they occur, they can put on quite a show---hitting hard one moment then retreating, only to return again.
A reinforcing punch of frigid arctic air within a powerful Canadian high pressure with an impressive 1043 mb. (30.80") central pressure is the driving force behind the Thursday lake snow-threat.
Air rising off comparatively warm lake waters encourages winds from both the eastern and western shores of Lake Michigan to sweep out over the lake where they converge, producing a "pile-up" of moist air just above the lake surface. This development leaves the air little choice but to ascend and cool, allowing it to generate a concentrated band of snowfall---sometimes no more the 10 or 20 miles across. Beneath this so-called "plume", snow may fall with abandon in bursts.
Many inland locations to miss-out of Thursday's snow----but broader coverage snowfall due late Thursday night and Friday with incoming Alberta Clipper
Lake snows, intense though they can be at times, are localized. Folks out in the Fox Valley or toward DeKalb, McHenry county or farther west in Rockford, Dubuque and Galena, may well miss out on Thursday's snow altogether. But, an Alberta Clipper approaching from the northwest is likely to bring wider-coverage light snow to the area starting late Thursday night and into Friday.
Friday snows could be the lackluster snow season's heaviest yet; 1 to 2" tallies appear best estimate
The early consensus on how much snow may fall with the Thursday night/Friday system is in the 1 to 2" range. While fairly modest totals compared to most seasons, such an accumulation could actually stand out this year given the fact that the current season's greatest single snow has been just 0.4".
Chicago's ten least-snowy winters through Jan. 24 have seen more frequent snows take place in back half of the season in February and March
The Chicago area may be at the vanguard of an atmospheric pattern realignment which could boost snowfall in the back-half of the current snow season.
Our analysis of 129 years of official weather observations suggests more frequent snows have often occurred in the Februarys and Marches of these low snow-producing seasons.