A major late-winter storm is expected to bury some parts of Long Island in snow Tuesday, buffeting the region with high winds and blizzard conditions before it charges out by day’s end.

The nor’easter had shifted westward as it approached the Island Monday, making it difficult to predict just how much snow would land where. What’s certain is that a powerful, fast-moving system is landing in the region overnight, creating dangerous driving conditions — especially during morning hours — and bringing some mass transit to a halt.

As of Monday night, the National Weather Service was calling for a range of 6 to 14 inches of snow for the Island, sustained winds of 35 mph to 50 mph and gusts of up to 60 mph. Blizzard conditions were expected throughout the morning, the Long Island Rail Road warned it might suspend operations, Gov. Andrew M. Cuomo declared a state of emergency and PSEG Long Island was bringing in hundreds of extra workers to cope with power outages and felled trees.

But the storm’s westward direction Monday did mean that Suffolk may be spared the worst.

“The heaviest snow, probably in excess of 12 inches, will be in Nassau and western Suffolk,” said Bill Korbel, News 12 Long Island meteorologist, with “much less” for the East End. Snow at times was expected to mix with sleet and rain, “especially along the South Shore and may change to all rain on the East End,” he said.

However, “as the storm develops, the area of mixed rain and snow may shift and that will be the biggest factor in determining final snow totals.”

advertisement | advertise on newsday

An update by the weather service was expected about 4 a.m. Tuesday.

Its Monday evening briefing — in which snowfall predictions came down slightly — said the storm’s track had continued to shift west with high winds helping to bring in the warmer air.

“Strong northeast winds will cause warmer air to wrap around the approaching intensifying low pressure system causing temperatures to warm above freezing across Long Island. . . . This will cause heavy snow to change to rain by noon, holding down snowfall amounts,” the briefing said.

Coastal flood warnings were expanded Monday evening to eastern Long Island bays, the briefing said, with a “moderate impact” called for there and on the South Shore.

County Executive Steve Bellone, in a 5 p.m. Monday news conference, said it appeared Suffolk could be spared the brunt of the storm, though he urged residents to use caution and stay off the roads if possible during morning rush hours.

“I want to emphasize there’s a lot of uncertainty,” he said. Despite the possibility Suffolk is spared the worst, he said, “We’re expecting a significant storm event.”

Suffolk Police Commissioner Timothy Sini said it would be a “messy storm.”

“If you can stay home during rush hour, that would be the best course of action,” he said.

Most Long Island school districts, federal and state courts and social services centers will be closed Tuesday.

The LIRR said it would evaluate operations Tuesday morning based on the weather.

advertisement | advertise on newsday

“If it is what they forecast . . . then it would be problematic to operate the railroads — LIRR and Metro-North. But we will update that as the storm actually progresses,” Cuomo said.

Nassau County Executive Edward Mangano said he anticipates keeping county roadways open through the storm, but urged residents who do not need to travel Tuesday to stay home.

“Common sense dictates that the high winds will create a significant visibility problem,” Mangano said at a news conference Monday at Nassau’s Office of Emergency Management, where the county leadership will monitor the storm. “So you should not venture to the roadways if the forecast remains on track. Stay home if you can.”

Suffolk County will suspend all Suffolk Transit fixed route and SCAT bus service Tuesday, according to county Public Works Commissioner Gilbert Anderson.

The Bridgeport & Port Jefferson Ferry, the New London-Orient Point Cross Sound Ferry’s casino connection service and the Hampton Jitney are also all canceled for Tuesday, according to their websites.

advertisement | advertise on newsday

The Nassau Inter-County Express, or NICE Bus, advised customers to “expect major delays, service modifications, detours and the potential of service suspension.”

“North Shore routes will become particularly difficult as the storm progresses,” NICE said in a statement.

The Port Authority said it expected hundreds of flight cancellations at the three area airports its operates: LaGuardia, Kennedy and Newark Liberty.

The agency said it had supplies of cots and other essentials for ticketed passengers who may be stranded at the airports.

The reconstruction of LaGuardia Airport creates special problems there, the agency said, and passengers should not go to the airport after the storm ends unless they have a confirmed reservation.

PSEG Long Island will get help from up to 1,500 workers from as far away as Florida to assist with power restoration and tree trimming should the storm knock out power.

The utility by Monday morning had secured the help of 1,000 power-line personnel and 500 tree trimmers from out of state to supplement the hundreds of workers already on the Island, spokesman Jeff Weir said.