A snow plow truck is loaded with salt. | File Photo: D. Allen Covey/VDOT (Creative Commons)

The National Weather Service has upgraded Lake County and McHenry County to a winter weather advisory ahead of possibly up to seven inches of snow Thursday into Friday.

A winter storm watch was issued Wednesday morning for Lake, McHenry, Winnebago and Boone counties.

The National Weather Service (NWS) later Wednesday afternoon issued a winter weather advisory for the four counties.

Cook, DuPage, Kane, Ogle, Lee and DeKalb counties are also under a winter weather advisory.

The advisory will go into effect from 3 p.m. Thursday until 7 a.m. Friday for McHenry County and 6 p.m. Thursday until 10 a.m. Friday for Lake County.

Heavy wet snow is expected with total snow accumulations of four to seven inches, the National Weather Service (NWS) said.

Snow rates are likely to peak near one inch per hour early Thursday evening.

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Travel could be “very difficult” and hazardous conditions could occur during the Thursday evening commute and the early Friday morning commute.

Snow accumulation is expected Thursday afternoon into Friday morning throughout much of the Chicagoland area. | Graphic via NWS

“The expected heavy, wet nature of the snow will make shoveling hazardous,” the weather advisory said.

Precipitation is expected to begin across the Interstate 39 corridor early Thursday afternoon.

It will spread east into the Chicago metro area by late afternoon and then into northwest Indiana early in the evening.

Precipitation will be mainly snow far northern Illinois transitioning to mostly rain south of the Kankakee River Valley, the NWS said.

The highest impacted area will be along the Illinois-Wisconsin border, the NWS added.

A flood warning is also in effect for the Fox River in Lake County and Kenosha County, Wisconsin.