Lake-effect snow doesn’t happen every day in Chicago. But, when the atmosphere produces a perfect amalgam of small and large scale atmospheric features,the lake snow machine is set in motion. The manner in which snow falls and accumulates in such situations is both fascinating and tricky to predict. Unlike the snowfall attending larger storm systems, which often falls over large areas and with fairly predictable variations in accumulation, the amount of lake snow which piles up in any one location is often influenced by comparatively tiny shifts in wind direction, the length of time over which snow falls, and the intensity with which it comes down, all of which can be modulated by small-scale terrain features like hills or moraines. These can change the amount of “lift” which takes place and that affects precipitation intensity. Areas of increased “lift” maximize precipitation, just as mountains do out West.
That perfect combination of atmospheric appears to be coming together Wednesday and Wednesday night in the counties adjoining Lake Michigan’s west and south shores. Northwest Indiana’s snow belt may well end up at the epicenter of the developing lake snow episode. If all unfolds as predicted, the hardest hit locations in sections of Lake, Porter and La Porte Counties, as well as in Berrien County Michigan, could be in for 8 to 12 inches of snow—or more. But lake snows are also predicted to sweep onshore in sections of northeast Illinois and eastern Wisconsin. Parts of Cook and Lake County Illinois may be in for 2 to 5 inches snowfalls if early indicators hold together.
A late season blast of cold arctic air, which sent readings tumbling as low as 10-below late Tuesday across sections of the Dakotas and Minnesota, sets the stage for this area’s lake snow. Jet streams strengthen as colder air arrives. The “lift” which cools air to saturation and aids in snow development, is especially vigorous beneath the leading edge or strong pockets of jet stream winds known as “jet streaks”. When further enhanced as cold air flows over warmer lake waters, the prospects for lake snow take off.
The process was clearly getting underway Tuesday evening as evidenced by falling barometric pressures and the development of a wind circulation east of Door County, Wisconsin. A feature referred to by meteorologists as a “meso-low”—”meso” referring to a medium-sized disturbance, as versus a “macro” or large scale system, was under development and expected to head south over Lake Michigan into Wednesday. Meso-lows in winter, when over large bodies of water have access to moisture that can set bursts of especially heavy snowfall into motion. As this disturbance settles closer to Chicago Wednesday afternoon and evening, the potential for the snowfall to grow heavier and more frequent in lakeside locations may well be enhanced. Just how intense how any resulting snow bursts become will influence accumulation.
Texas hit by snow again; same system could bring eastern U.S. mountains snow measured in feet
The same southward plunge of cold arctic air helped fuel the latest round of snow to hit Texas and the Deep South Tuesday. By evening, the heaviest snow totals in the Lone Star State included 6.0 inches at Sweetwater, 5.3 inches Palestine, 5 inches Baird, 4.4 at Midland (a new record for the date) and 3.5 at Waco. That eastbound disturbance is to proceed off the Florida coast Wednesday where it will begin intensifying explosively. The mammoth storm which results is to continue north then stall over the Mid-Atlantic just north of New York City late in the week and into the weekend. Its slow pace of movement should keep snow piling up across the region prompting the issuance of winter storm watches from Washington D.C. to Philadelphia, Atlantic City and much of interior New York and New England. Mountainous areas there could measure snowfall in feet over coming days—while areas like New York City, where heavy rain is to fall first, are to expected to experience a switch to snow which may produce significant accumulations amid howling winds.
The mammoth system’s reach could ultimately extend westward into the Midwest bringing clouds and some periods of light snow to Chicago toward the weekend. Gusty winds here in coming days will be increasingly related to the deep storm’s circulation.
Late season arctic chill to bring Chicago its chilliest daytime temps in 10 days
Daytime highs in the 20s Thursday would be the coldest to occur in Chicago since a 28-degree high on Feb. 15.