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.
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.
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.
http://blog.chicagoweathercenter.com/2013/01/24/concentrated-plume-of-lake-moisture-targeting-lakeside-counties-with-localized-possibly-heavy-bursts-of-snow-quick-1-to-2-totals-may-occur-in-heavier-squalls/
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