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(CHICAGO) More than 400 flights have been canceled as Chicago prepares for up to 5 inches of snow by Monday afternoon.

As of 3 a.m. Monday, 399 flights were canceled at O’Hare International Airport and 52 flights had been canceled at Midway International Airport, according to the Chicago Department of Aviation. Average delays at both airports were running about 15 minutes.

Snow started falling at O’Hare about 9:45 p.m. Sunday, but less than an inch had accumulated by 1 a.m. Monday, said National Weather Service meteorologist Kevin Donofrio.

A winter weather advisory was in effect until 1 p.m. Monday, with between 2 and 5 inches of snow accumulations expected in Lake, DuPage and Cook counties. Visibility will be reduced during periods of heavy snowfall and could make for difficult driving conditions, the weather service warned.

“The intensity of the snow will vary from time to time until (Monday) morning,” said meteorologist Gino Izzi. “It seems pretty likely we’ll be experiencing snow during rush hour, so I would plan on a longer than usual commute.”

Izzi said this will be the first time Chicago has recorded at least one inch of snow since Dec. 17, 2016, marking the city’s longest streak without snow ever recorded during the winter.

Lake effect snow could then develop Monday evening and continue overnight into Tuesday, adding to snowfall accumulations, the weather service said. Lake effect snow, which can produce very heavy snowfall, sometimes in excess of 2 inches per hour, could continue periodically throughout Tuesday morning.

Temperatures were expected to reach a high of about 30 degrees on Monday, the weather service said. The chance of snow was about 100 percent on Monday, with wind gusts as high as 20 mph. A high near 27 degrees was expected Tuesday, with an 80 percent chance of snow.

The city’s Department of Streets and Sanitation deployed 287 snow plows overnight to tackle the snowy weather. The plows focus on salting and plowing arterial routes to ensure the roads are safe before moving to neighborhood streets, if necessary.

While Chicago braced for its first snowfall in months, larger snowstorms were expected on the East Coast. A blizzard watch was issued for the Boston area, with 12 to 18 inches of snow expected to fall over eastern Massachusetts as well as central and southern Rhode Island, according to the weather service.