UPDATE: Forecast improving. Now expect about 10 inches by Sunday.

CHICAGO (CBS) — A total of up to 17 inches of snow could fall by the end of the weekend, a worst-case scenario that could put this event on par with some of the biggest in history.

Starting tonight, snow will start falling and intensify overnight, with 6 to 12 inches of snow on the ground by noon.

Some isolated areas may see 14 inches of snow on the ground. Schools and businesses were already announcing closings

Then, a second event will sweep into the area on Saturday, with one to three inches possible.

If the storm dumps numbers in the higher range, the 17 inches would put it among the biggest ever. However, for record-keeping purposes, the entire event might not be considered one single storm.

The band of the heaviest snow is fairly narrow, so totals could vary.

With so much snow on the way, local and state road crews were planning for a very busy start to the weekend, in an effort to keep roads clear.

The Illinois Department of Transportation maintains a fleet of 1,700 trucks used to plow and salt nearly 16,000 miles of Interstates and other state roads across Illinois when it snows.

Last year, IDOT used more than 300,000 tons of salt.

Meantime, the Chicago Department of Streets and Sanitation will deploy its full fleet of plows Thursday night. When it snows, the city starts by plowing and salting the city’s main streets and Lake Shore Drive until the snow stops, then starts clearing side streets.

“We are going to be working all night [to clear the streets],” Mayor Emanuel said at a news conference on Thursday. “Leave yourself time to get to work and get home.”

The mayor urged residents to check on sick and elderly neighbors to make sure they are safe.

“The city is ready for this,” Emanuel said. “This is a heavy snow, the heaviest we have seen in a couple of winters.”

Given that this storm is expected to last a full day, some side streets might not get plowed until Friday night.

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