11pm observations indicate that the rain that has dampened portions of the Chicago area this evening is in the process of changing to snow as cooling continues. With temperatures still above freezing the snow will initially melt on the pavement but as the rate of fall increases and temperatures continue to drop pavements will gradually become snow covered and slippery.
The snow will accumulate overnight with accumulations at the rate of 1 to 2 inches an hour possible in areas where thundersnow occurs. By the time the snow tapers off Wednesday morningv accumulatrions should generally be in the 4 to 8 inch range across much of the Chicago Metro area, except lighter north and wesst of the city towards Wisconsin and Rockford where 1 to 4 inches may fall. Some locally heavier totals in excess of 8 inches can’t be rule out in areas where repeat thunderstorms occur.
By Meteorologist Richard Koeneman
Walt Kelly (1913-1973), creator of the comic strip “Pogo,” once remarked, “What’s good about March? Well, for one thing, it keeps February and April apart.” Kelly understood that March, more than any other month, can manifest the temperature and weather characteristics of both winter and summer.
This year, Chicago’s March is off to a decidedly tumultuous start, and, following a cold and snowy winter, the city is approaching a snowfall milestone. The overnight storm that delivered thunderstorms and heavy, wind-driven snow has carried this snow season’s cumulative snowfall to within striking distance of the city’s all-time snowfall record: 89.7 inches during the winter of 1978-79. As of March 11, the season snow total stood officially at 75.5 inches as measured at O’Hare International Airport (and 79.2 inches at Midway Airport).
As the weather warms this spring, we will begin to have extended periods with above-freezing temperatures. What is the longest period the city has gone without dropping to 32 degrees or lower?
— John Hastings, Niles
Chicago’s growing season — the period between the last freeze in spring and the first freeze in autumn —typically runs about six months, from mid-April to mid- or late October. In 1931, however, the last spring freeze was April 2 and the first autumn freeze was delayed until Nov. 24, a record 236 days later. The exceptionally late autumnal freeze was a direct result of the location of the city’s official thermometer on the University of Chicago campus, near the mild water of Lake Michigan. At Midway Airport, the first 32-degree fall reading occurred more than three weeks earlier, on Nov. 1.
A look at the latest WGN in-house RPM model shows the rain changing to snow in the next few hours changing to heavy snow in the post midnight hours The heavy wet snow is expected to accumulate rapidly overnight with total accumulation ranging from 1 to 4 inches north and west to the city to 4 to 8 inches in areas from the city and south. Some of the snow will be accompanied by thunder and will fall intensely with accumulation of 1 to 2 inch an hour possible.
Travel conditions will quickly deteriorate after the snow begins and strong gusty northeast winds will cause some blowing and drifting of the snow. The snow is expected to taper to flurries by early Wednesday morning but cause problems for the morning commute.
Winter storm warninga are posted for much of the Chicago Metro area with the exception of areas well north and northwest of the city.
Lemont- Pea size hail at 127th and Archer at 9:13pm
The opening round of tonight winter storm is spreading into the Chicago area this evening in liquid form as a band of showers and thunderstorms, some with small hail, arrive. However, to the north across far southern Wisconsin the precipitation is changing over to snow.
At 9pm snow or sleet was being reported at Racine, Milwaukee, Burlington and Waukesha. As colder air filters into the area, coupled with cooling from evaporation and cooling from increasing vertical motion, the precipitation in the Chicago area should change over to snow later this evening north of the city and in the post midnight hours from the city and areas south.
At 8:30PM CDT numerous showers and a few thunderstorms have developed in the past hour back to the west and southwest of Chicago (see current weather radar above). The showers are moving east-northeast, and should reach the Chicago area within the next hour or so. Some will produce pea-size hail. So far this evening pea to marble-size hail has been reported at Morris, Mendota and Princeton and Galva.
At the same time temperatures have fallen into the mid to upper 30s area-wide as strong northeast winds continue to pull cold air off the icy cold Lake Michigan. Chicago-area dew-points have settled into the upper 20s to lower 30s for the most part.
So the stage is set for a cold rain to settle into our area with a changeover to sleet and then a wet snow still looking viable later this evening.
8:15PM CDT temperatures