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
