UPDATE: Winter Weather Advisory Upgraded to Warning for Friday

UPDATE, Jan. 19, 10 p.m.

The National Weather Service has upgraded the winter weather advisory to a winter storm warning. The snow is expected to arrive in mid-to late morning and total accumulations of 5 to 8 inches are expected. 

A watch is upgraded to a Winter Storm Warning when 4 or more inches of snow or sleet is expected in the next 12 hours, or 6 or more inches in 24 hours, or 1/4 inch or more of ice accretion is expected, according to the NWS.

UPDATE, Jan. 19, 3:05 p.m.

The National Weather Service has now issued a winter weather advisory for Friday. The winter storm watch is no longer in effect.

The advisory will be in effect from 9 a.m. Friday until midnight. According to the National Weather Service, the snow is expected to start falling during the mid- to late-morning hours, with the heaviest snow forecast to fall in the afternoon. About 3 to 6 inches of snow is expected, with locally higher amounts possible.

The National Weather Service has issued a winter storm watch for all day Friday for northern Illinois including Lake, Cook and McHenry counties.  

Snow is expected to start falling in the morning and will be heaviest in the afternoon and early evening, when snowfall rates could be as much as one inch per hour.

Snow total accumulations could be six inches or more. Traveling during Friday evening rush hour is expected to be slow and could be hazardous.  

According to WGN meterologist Tom Skilling, forecast scenarios being put out by virtually all computer models are showing atmospheric conditions that could produce the heaviest snowfall of the season. 

“Forecast models from the U.S., Canada and Europe have all converged in recent days on the same solution, each placing Chicago in or near the corridor of maximum snowfall,” said Skilling in the Chicago Weather Center blog.