UPDATED 02/23/12 9:20 p.m.

CHICAGO (CBS) – You might have forgotten that it’s February, and that winter is not over.

You also might have figured that given how late it is in the season, we must be in the clear when it comes to major snowstorms.

But it is February, and it is winter. And the Chicago area got a major reminder of that on Thursday night.

CBS 2 Meteorologists Megan Glaros and Steve Baskerville report a winter storm watch and a winter weather advisory for all Chicago area counties from Thursday evening until Friday morning. The advisory may still be upgraded to a winter storm warning, as is already in place across the lake on the west coast of Michigan.

Snow began falling in the northwest suburbs on Thursday afternoon. Rain was still falling in the city around 5 p.m.

The storm resulted in the hundreds of flights being canceled by mid-evening. At O’Hare International Airport, more than 350 flights were canceled. Some flights were also being delayed up to 45 minutes, the Chicago Aviation Department reported.

At Midway Airport, 100 flights had been canceled, the department said.

There area was expected to be slammed with a heavy, thick snow that will be a challenge to shovel. Overnight, the snow could fall at a rate of 2 to 3 inches per hour.

There might even be bouts of “thundersnow,” a condition the area hasn’t seen since the infamous Blizzard of 2011 dumped 21.2 inches of snow on the city.

In the north suburbs, Dave Hendricks was preparing for the storm by filling up a gas can for his snow blower.

“This is the first can I’ve had to buy,” Hendricks, commenting on this winter’s mild weather, told CBS 2’s Derrick Blakley.

In Waukegan, schools were planning to start two hours late Friday.

Glaros has revised earlier estimates of 6 to 9 inches to a modestly lighter 4 to 7 inches from the city of Chicago proper north to the Wisconsin state line, and west all the way to the Mississippi River. But depending on when the transition from rain to snow happens, snowfall of 9 inches was still a possibility.

The snow will continue to fall violently on Friday morning. The system is not expected to move out until lunchtime, and thus, Chicagoans should prepare for a treacherous morning commute.

The fact that the snow will be so heavy is actually keeping projected accumulation totals down. Glaros says if the snow were light and fluffier as is often seen earlier in winter, the totals could be closer to a foot.

To the south, Will and Kankakee counties can expect about 2 to 4 inches, as they will see the transition from rain to snow later in the evening. To the north in Wisconsin, 2 to 4 inches are also expected.

The totals could wind up being lower if the rain-snow transition happens later than 9 p.m., Glaros says.

When Friday comes around, the high climbs only to 36 degrees. Conditions will be sunny on Saturday, but the high will only reach 34.

But on Sunday, the high returns to 42.