2nd straight December to open with a storm system
December 2007 dawns much as the month did a year ago -- with the season's first significant winter storm in the area. While a 6-8 hour period of sleet and freezing rain starting this afternoon is the major threat with this year's storm, snow was coming down hard as Dec. 1 got underway a year ago. The thundersnow which accompanied the wintry system was a product of cloud tops scanned to heights of 30,000 feet -- unusual in a cold-season storm -- and so loud, it set off car alarms. By the time that system exited, 6.2" had been measured at O'Hare and 3.3" at Midway; some northwest suburbs were covered by nearly a foot of snow.
The scope of Saturday's storm is remarkable. Sections of 24 states were under winter storm advisories Friday night. Ice may accumulate as sleet falls, then shifts to freezing rain. Supercooled droplets falling into the subfreezing air will freeze on contact with colder outdoor surfaces until temps rise above freezing late tonight.
--By Tom Skilling, WGN-TV Chief Meteorologist