Most of northern Illinois is under a winter storm warning was that was issued Friday afternoon by the National Weather Service.
It revised a storm forecast from earlier Friday that had showed the storm skewing more to the northwest. The new track shows it encompassing nearly all of northern Illinois.
All counties north of Interstate 80 — with the exception of Jo Davies and Stephenson counties — are now included in the zone. A winter watch continues for those two most northwestern counties, in any event.
The storm zone also includes counties south of the I-80 corridor, including Putnam, Marshall, Tazewell and Livingston counties, as well as those to the north, including all of Will, La Salle, Kendall, Grundy, Kane, DeKalb, Lee, Ogle, McHenry, Boone and Winnebago counties.
The revised forecast showed the storm moving north and east across the state. Areas south of a curving line from Dixon to Ottawa to Pontiac could see the first effects of the storm by 9 a.m. The first snow could hit areas north of that line at about 10 a.m. A line from Rockford to Elgin to just north of Joliet reaching toward the Kankakee County line could see storm effects by 11 a.m.
The Illinois Department of Transportation urged motorists to postpone unnecessary travel.
“IDOT crews will be out on the roads but conditions could still be extremely hazardous, so we encourage motorists to ask themselves if they really need to make the trip,” said Transportation Secretary Omer Osman.
He added that bitter cold temperatures, which are expected through the Monday, reduces the effectiveness of materials used to treat roadways for snow and ice.
The forecast calls for heavy snow, gusting winds and subzero wind chills starting about 6 a.m. on Saturday.
Snow: Accumulations of four to eight inches are expected.
Winds: Gusts as high as 35 mph in a northeasterly direction.
Cold: Wind chills, which has the potential to cause frostbite on exposed skin in as little as 30 minutes. The Sauk Valley could see wind chills of 15 below zero by Monday.
If people must travel, IDOT says, they should expect blowing snow could reduce visibility, especially across east-west roads. Motorists are advised to have a cell phone, warm clothes, blankets, food, water, first-aid kit, washer fluid and an ice-scraper in their vehicle. They should also approach areas prone to icing with caution.
IDOT said that should motorists breakdown or be involved in a crash, the safest shelter is within the vehicle.
The storm is moving in a northeasterly direction and could dump as much as eight inches of snow in areas south of Interstate 80. It is expected to approach Burlington, Iowa, by 6 a.m., the Quad Cities about 8 a.m. and the southern portion of Whiteside County sometime after 9 a.m.
The weather service also issued a frigid weather warning, projecting wind chills for the region. Sterling wind chills start at 13 degrees at noon on Saturday, gradually falling to 1 degree by 6 p.m. Overnight Sunday, wind chills will be around minus 8 degrees, eventually dropping to minus 11 degrees by 6 p.m. Monday will feel even colder, wind chills plummeting to 15 below in the morning before rising above zero about noon.