The National Weather Service has upgraded to a winter storm advisory for a potential winter storm system that could bring several inches of snow to the Chicagoland area on Wednesday.
The National Weather Service (NWS) initially issued a winter storm watch on Monday for Lake, McHenry, Boone, Winnebago, DuPage, Cook, Will, Kane, DeKalb, Ogle, Lee, LaSalle, Kendall, Grundy and Livingston counties.
The weather service on Tuesday upgraded the watch to a winter storm advisory, which will go into effect at 9 a.m. Wednesday.
A winter storm system will impact the northern Illinois area on Wednesday into Thursday morning.
The advisory said snow, possibly heavy at times, is expected bring total snow accumulations of three to six inches.
Forecasts charts from the NWS initially showed on Tuesday an 81% chance of six inches or more of snow in Waukegan and a 73% chance of six inches or more of snow in Chicago.
Those estimates have since been scaled back to a 53% chance of six inches or more of snow in Waukegan and a 30% chance of six inches or more of snow in Chicago.
The NWS said the heaviest snow will generally be between 11 a.m. and 5 p.m.
The weather service shared a timeline of the event and said that bands of mainly light snow, primarily Interstate 80 and north, will occur pre-dawn Wednesday through 10 a.m.
The main system of snow will overspread the northern Illinois area from west to east from 10 a.m. to 12 p.m.
From 12 p.m. until 6 p.m., periods of moderate to briefly heavy snow, possibly an inch per hour, will likely result in a few to several inches of accumulation, the NWS said.
Snow and slush will cover the roads and a much longer than usual commute is expected, the weather service said.
From 6 p.m. to 12 a.m. Thursday, light to moderate snow will continue in parts of the area with additional accumulation of a few tenths to up to two inches.
Snow could mix with or even change to freezing rain on Wednesday evening, according to the NWS, with the highest chances appearing to be south of Interstate 80.