At 5:20PM, weather radar revealed a mixture of light precipitation overspreading much of the Chicago area south of the Northwest Tollway-Kennedy Expressway line.
Surface reports indicate that most of the precipitation is a mixture of rain, sleet and snow with little or no accumulation so far. Once the stronger dynamics of this storm kick in, the predominant precipitation type will quickly switch over to all snow. Bursts of heavy snow become increasingly more likely after 8PM.
At 3:45PM, radar and surface reports indicate that a mixture of rain and sleet has started to fall across many south and southwest Chicago suburbs. The rain and sleet is expected to change over to snow later this evening as temperatures cool not only at the surface but also aloft.
At 2:30 this afternoon, rain and snow continues to streak out of Iowa and Missouri toward the Chicago area. There are no changes to the WGN Weather Center forecast for this storm. We are still expecting between 5 and 9 inches of snow for a majority of the Chicago area. The precipitation will likely start out as rain or a rain/sleet mix before changing over to snow this evening.
The lone exception to the 5″ to 9″ forecast will be south of Interstate 80 and east of Interstate 55, or over Kankakee, southern Will, far southern Cook, Lake (IN) and Porter (IN) counties where 2″ to 6″ is expected. These areas will likely see some periods of sleet or perhaps even rain, which should cut into the snowfall totals there.
The snow will begin between 4PM and 8PM, with bursts of moderate to heavy snow likely from 7PM until 4AM. New computer model guidance arriving at the WGN Weather Center confirms the heavy snow potential, with snowfall rates of 1″ per hour possible after 7PM. Road conditions should deteriorate rather rapidly as the evening progresses as road crews struggle to keep up with the rapidly falling snow.
The snow will diminish to flurries or end rather rapidly Monday morning between 6AM and 9AM.
Snow is expected to begin in the Chicago area late this afternoon or evening as the next winter storm begins. Shortly before 1:30 p.m. the leading edge of the band of snow was crossing the Mississippi River from near the Quad Cities and extending southwest thorugh northwest Missouri and the Kansas city area into northeast Kansas.
Areas in southern Iowa have been reporting periods of heavy, wet snow. Some early totals include…
Cantril Iowa 1.3 inches
Burlington, Iowa 1.3 inches
Macomb, Illinois 1.0 inches
Downing, Missouri 1.5 inches
Fort Madison Iowa 2.5 inches
Augusta, Illinois 1.0 inches
Le Harpe, Illinois 2.0 inches
Here is a list of counties included in the Winter Storm Warning from 6PM tonight until Noon Monday:
Lake (IL), McHenry, Boone, De Kalb, Kane, La Salle, Kendall
The following is a list of counties under a Winter Weather Advisory from 6PM until Noon Monday:
Cook (Including Chicago), Du Page, Grundy, Will, Kankakee, Lake (IN), Porter (IN)
5″ to 9″ in both the Advisory and Warning counties.
2″ to 6″ in the Advisory areas south of Interstate 80
White: Snow Advisory/Winter Weather Advisory
Yellow: Winter Storm Watch
Red: Winter Storm Warning
UPDATE: 11:55AM: Still awaiting details from the National Weather Service on who is in, and who is out of the Winter Storm Warning.
The Winter Storm Watch has been replaced with a Winter Storm Warning for some northern and western suburbs. It appears that the City of Chicago and Cook County will not be under the new warning.
Details will follow shortly.