You either received snow Thursday or you didn’t. There was virtually no middle ground. And where the snow fell, it did so with vigor, producing the heaviest single-storm snow accumulations of the 2012-13 season.
It was the northern half of the Chicago area over which accumulation grew most impressively from late morning forward. Huge flakes, some nearly an inch in diameter, fluttered to earth in such numbers that visibilities were slashed to fractions of a mile. There were even reports of thunder, signaling vigorous upward motion in the atmosphere, a development which maximized precipitation intensity.
By mid-afternoon, snow accumulations had increased dramatically, producing such icy surfaces that hills became insurmountable—a development which forced road closures. Afternoon and evening commuters found themselves saddled with horrendous road conditions which led to commute times at times hours in length.
Among the more significant accumulation reports by late Thursday evening (with some light snow still falling) were: 9.5” at Zion, 9” Kenosha; 8.5” Beach Park, 7.8” Vernon Hills, 7” Wadsworth and Gurnee, 6.5” Bull Valley and Winthrop Harbor, 6” Grayslake, 5.5” Lake Bluff, 5.3” Lake Zurich, 5.1” Mundelein, 4.9” DeKalb and 4.6” at Northbrook.
While local 2 to 3” totals were reported in sections of Chicago’s north side, O’Hare had only 1” of snow while just 0.5” fell at Midway Airport.
Thursday’s snow a non-event south half of metro area
While Thursday’s heavy snowfall produced scenes that can only be described as “winter wonderland-like”, accumulating snow was a NO-SHOW to the south. The transition to sleet then snow which occurred farther and farther south during the afternoon, for all intents and purposes failed to make it into Chicago’s southern suburbs denying that region any accumulation.
Disturbance behind Thursday snows here to combine with explosively-intensifying Atlantic storm to produce a potentially historic Northeast U.S. blizzard
The disturbance behind Thursday’s snowfall in portions of the Chicago area is to combine with a second system which tracked across the Southeast U.S. overnight. As the two systems merge, explosive intensification is to begin. In short, the system is predicted to “bomb-out”, a phrase used by meteorologists to describe a storm which deepens by at least 1 mb. per hour for a minimum of 24 hours.
The storm sweeping out over the northbound Gulf Stream’s warm, energy-rich waters off the East Coast is to initially do so with a central pressure of 1011 mb (29.85”) but is to drop precipitously to 969 mb (28.61”)—an eye-catching barometric pressure drop of 42 mb in under 24 hours.
Pressure drops of that magnitude lead to strengthening winds—a development which, in this storm's case, is likely to produce gusts exceeding 70 mph over coastal and nearby sections of the Northeast.
Boston’s all-time snow record of 27.6”, dating back to a 2003 President’s day weekend storm, appears vulnerable
Predicting a weather record of any kind is a dicey proposition. Forecasters avoid doing so until satisfied such an occurrence is a real possibility. The historic probability of replacing any record isn’t overwhelming to begin with—but never is that truer than when it’s an ALL-TIME low which is being challenged.
Having said that, the consensus of a suite of computer models could put Boston’s 2003 record of 27.6” within reach.
Storm-generated snowfalls in the 1 to 3 ft. range amid near-hurricane force wind gusts threaten widespread power outages
The region of the Mid-Atlantic and Northeast being targeted by what looks to be a historic Friday/Saturday East Coast storm is still reeling from the effects of Sandy. Not only may the super-charged storm sweeping into the region produce hurricane force gusts, but the heavy accumulations of snow predicted is likely to take power-lines down, producing dangerous power outages.
Coastal flooding a risk in areas still reeling in Super-storm Sandy’s aftermath
Any time winds of the strength predicted Friday and Saturday blow onshore—as the latest storm’s northeast flow will do—rising tides result, increasing the risk of coastal flooding.