With a powerful blizzard expected to blanket Massachusetts with up to 3 feet of snow, Governor Deval Patrick ordered non-emergency state workers to stay home, urged people to get off the roads by noon Friday before the storm intensifies, called for all local school districts to cancel classes, and announced that the Boston area’s public transit system would shut down.

The nor’easter arriving Friday morning could drop 2 to 3 feet of snow that would be lashed by winds gusting up to 65 miles per hour into drifts as deep as 5 feet, the National Weather Service said this afternoon.

Issuing blizzard warnings for all of Eastern and Southeastern Massachusetts, the service warned that the potentially historic storm would pose a threat to people’s lives and property and that conditions would deteriorate quickly as the storm develops Friday.


“The sooner you can be off the roads the better,’’ said weather service meteorologist William Babcock. “You want to give yourself some time to be at your safe spot before the storm hits its strongest.’’

Forecasters said that heavy snow, blowing and drifting, could cut visibilities to a quarter-mile, causing white-out conditions. The winds, which could reach 65 miles per hour, could also damage trees and structures and bring down power wires, causing scattered power outages. Temperatures will be in the mid-20s and the forecasters cautioned people to stay indoors.

A National Weather Service snowfall total forecast map issued this afternoon shows a swath of the state north and south of Boston getting more than 2 feet of snow, with amounts tapering off somewhat to the west and south, where the island of Nantucket is expected to get only up to 6 inches and the outer Cape only as much as 8.

The forecasters are also warning that the storm will produce moderate coastal flooding Friday evening and moderate to major coastal flooding Saturday morning. Large waves, along with a 2-to-3-foot storm surge, are expected to devour beaches and flood shore roads. They also may put shoreside homes at risk during the Saturday morning high tide.


Flanked by a number of other top state officials at a late afternoon news conference today, Patrick urged people to stay off the roads after noon, saying the brunt of the blizzard would start to be felt between 2 p.m. and 5 p.m. Friday.

He said drivers in recent storms had been cooperative, but “if I have to order the roads be cleared, I will.’’

In addition to letting state workers work from home, Patrick encouraged private employers to let their workers stay home.

The MBTA will shut down at 3:30 p.m., with the last trains and buses leaving from downtown at that time, said Transportation Secretary Richard A. Davey.

Davey said highway crews would be out in force tonight and into Friday morning, treating roads with rock salt and brine, then the crews would be briefly rested “because we’re expecting our crews to be working pretty darn hard’’ during the peak of the storm later Friday.

Patrick also said he had called up 500 National Guard members to help in storm recovery efforts, who would be able to join with 500 full-timers already working on Friday. Another 5,000 to 6,000 were slated for training over the weekend. That training has now been canceled so they will be available, he said.

Patrick outlined a number of safety measures that people should take, including obeying any evacuation orders, having plenty of food and water on hand, and getting a full tank of gas before the storm hits. The governor also suggested that people should check on elderly neighbors and shut-ins.


“Be a good neighbor, everybody,’’ he said.

Energy and Environmental Affairs Secretary Richard Sullivan said that all four major utilities that supply the state with electricity have begun extensive preparations. He said the utilities are “at the highest level of bringing in outside resources’’ to assist.

Sullivan added that while all providers have thorough plans in place, “the utilities will be measured by their response on the ground.’’

Patrick reminded people that power restoration efforts would not begin until after the storm ends.

State Fire Marshal Stephen D. Coan urged people to make sure their flashlight batteries are fresh and that smoke and carbon monoxide detectors are working. He also said to make sure that all exterior vents are cleared to prevent carbon monoxide buildup.

And, Coan cautioned, in the event of a power outage, “battery-operated flashlights and candles are the safest way’’ to provide light. He said generators should be kept outside, and gas and charcoal grills should not be run in enclosed spaces.

Patrick said officials will constantly monitor the storm’s trajectory and respond accordingly.

“Mother Nature is so unpredictable,’’ he said. But, at the same time, he said, “This team has had a lot of practice. We work very, very well together.’’

Boston Mayor Thomas M. Menino urged people to stay off the roads Friday and canceled school, and he was far from alone as scores of other school systems around the state followed suit.