SEVERE WEATHER UPDATES: December 2008 Archives

Tonight's snow to wind down in a few hours...another storm to follow Thursday night-Friday

The snow will be gradually winding down across the Chicago area as the evening wears on with only flurries expected in the area by about 10 p.m. Through 6 p.m. storm snow totals were approaching 4 inches at O'hare and 3 inches at Midway. By the time the snow ends area most area totals should be in the 4-6 inch range.

Before this storm's snow is even cleared, forecasters are already taking note of another storm that threatens the Chicago area during the late-Thursday-Friday period. This storm will have considerably more moisture to work with than tonight's storm and temperatures will be warmer so the area could be facing a messy mixture of heavy snow, ice and even rain before it is over. Winter storm watches are already posted across southern portions of Wisconsin and Lower Michigan and may be issued for northern Illinois and the Chicago area by Wednesday morning.

Beyond that another snow threat looms late Saturday and Sunday followed by an arctic blast that could bring the season's first widespread subzero temperatures.

Stay tuned!!

Steve Kahn WGN-TV/Chicago Tribune Meteorologist

Lake effect snow has developed Tuesday morning ahead of the main "system snow" due to overspread the area this afternoon and continue Tuesday night

Lake effect snow has developed in areas along Lake Michigan Tuesday morning in advance of the main snow expected to be generated by the latest wintry weather system to affect the area this afternoon and tonight. Light easterly winds and the intense cold situated over and adjacent to Lake Michgian are to blame for the early onset of lake-effect snow in areas closest to Lake Michgian including the city of Chicago.

The amount of snow weather systems produce is linked in part to the temperature of the atmosphere through which their snowflakes fall. While most weather systems produce snow in a ratio of about 10 inches for every inch of moisture available to them, temperatures with the Tuesday/Tuesday night system are at levels which will approximately double the volume of snow which falls from the roughly 0.30" water equivalent moisture the current disturbance is to generate. It's likely this system will produce 15 or 20-to-1 ratio snow. In other words, snowflakes will be fluffier and have one and a half to two times the volume of most systems' snow here. It if for that reason, our accumulation predictions have been set at 3 to 6"--where in a warmer environment, a system with the same level of moisture available to it might be expected to produce only 3" of snow. Since the city and southern suburbs have yet to receive a 3" or greater snow to date this season (our northern and northwest suburbs already HAVE seen 3"+ snows)---the current system is to produce the city and southern suburb's heaviest snow to date this season. Weather updates will be issued as necessary.

Tom Skilling
Chief Meteorologist-WGN-TV/Chicago Tribune