With a snowstorm expected to blanket Boston before dawn Wednesday, Boston Mayor Martin J. Walsh moved tonight to cancel school and impose a parking ban.

Between 6 and 10 inches of snow could fall in Boston, most of it before 1 p.m., National Weather Service meteorologist Eleanor Vallier-Talbot said. Worcester County could get 10 to 14 inches.

“It looks like most of the heavy snow is going to be along and below the [Massachusetts Turnpike] and into Worcester County,” Vallier-Talbot said.

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A winter snow emergency and parking ban will take effect at 11 tonight, Walsh said in a statement. Boston public schools will be closed Wednesday.

Parking will not be allowed on most major streets once the ban goes into effect. A list of the streets affected by the ban and alternative parking areas can be found on the city’s website.

On smaller streets, cars must be parked no more than 1 foot from the curb and at least 20 feet from an intersection.

Snow should be lightest on the South Shore, where higher temperatures could result in a mixture of rain and sleet, weather service meteorologist Alan Dunham said.

“It’s not going to be fluffy snow. It’s going to have a higher water content,” he said. “This is going to be the heavy, wet snow that if you’re out shoveling it and aren’t in good shape, you could have a heart attack.”

Snow should arrive between 3 and 5 a.m. Wednesday, falling lightly at first and increasing in intensity after 7 a.m., Dunham said. Highs will crest at 33 degrees in the afternoon, with snow falling at up to 2 inches per hour in some areas.

“If your morning commute includes driving, plan on it taking a very long time,” Dunham said.

The storm will exit the region Wednesday evening, with temperatures dropping to 21 degrees and less than an inch of further accumulation between the late afternoon and overnight hours.

“Thursday and Friday are still looking wonderful, with mostly sunny skies and chilly temperatures,” Dunham said.

Highs Thursday should be near 29 degrees, dropping to 14 degrees in the evening. Friday should be similar, with temperatures rising into the upper 20s, and plunging to 15 degrees overnight.