Staff report

A potential nor'easter could blanket counties along Lake Ontario with more than a foot of snow, according to the National Weather Service in Buffalo, which updated the event to a winter storm warning Sunday afternoon.

The Weather Service also extended the winter storm warning from 8 p.m. Monday evening through 8 p.m. Wednesday evening for Monroe, Wayne, and northern Cayuga counties. Ontario and Livingston counties were removed from the original winter storm watch.

The storm could bring heavy and blowing snow to the Rochester area, with accumulations of 8 to 16 inches possible in some areas and very poor visibility for driving and deep snow on roadways.

Wind speeds will range between 20-30 mph with gusts up to 40 mph possible.

► Rochester windstorm: What you need to know Sunday

► More; Gov. Andrew Cuomo critical of RG&E's windstorm response

► Interactive map predicting snowfall

The heaviest accumulations are expected Tuesday and Tuesday evening.

Already, several Monday flights have been cancelled and delayed at the Greater Rochester International Airport because of the storm.

Irondequoit Supervisor Dave Seeley, posting on the town's Facebook page that the Winter Storm Warning "...has added a new level of concern to this already serious emergency, Our town has already begun to mobilize for this upcoming severe event, even as recovery from Wedesday's wind storm continues."

The storm is predicted to bring more than 6 inches of snow to Washington, D.C., northern Maryland, New York, central and eastern Pennsylvania and a large part of New England.

Why the higher amounts here? Along Lake Ontario, "potentially the bulk of the snow … will be lake effect or lake-enhanced," said Bob Hamilton, a meteorologist in the Buffalo office.

The Weather Service warned that any change in track could dramatically alter the amount of snow and where it falls. But there is little doubt that a big storm will explode on the region, says Tom Kines, senior meteorologist for AccuWeather.

"A lot would really have to go wrong, so to speak, for this system to not deliver a ferocious punch," Kines told USA TODAY. "The reality is we are just hemming and hawing over snow amounts. Who gets 6, 12 or even 18."

The wet, heavy snow combined with the high winds could mean damaged trees and powerlines and blocked roads. Washington, Baltimore, Philadelphia, New York and Boston all could face a direct hit, meaning airport disruptions could prompt flight delays and cancellations across much of the nation.

Philadelphia International Airport tweeted that some airlines would be issuing travel waivers and urged travelers to contact their carriers. With snow already roling across parts of the Midwest, airlines canceled more than 100 flights Sunday and and more than 500 on Monday, according to FlightAware. American, Delta and United were among carriers offering no-cost waivers for flights Tuesday and Wednesday at dozens of airports from Virginia to Canada, if flights are rescheduled by Friday.

"Anybody looking to travel on Tuesday, whether by land or air, will find it difficult or impossible in many places," Kines warned.

Kines said two "pieces of energy" were involved. A storm system was dumping heavy snow across the Northern Plains on Sunday and was heading east. Another storm system will try to form Monday off the South Carolina coast, he said.

"That storm is going to take control," he said. "The big cities will probably fall into the 6- to 12-inch category. But there will be places that get 12 to 18. And it's not out of the question that New York or Boston will be among those places."

The National Weather Service issued a blizzard watch from New York City and Long Island to southern Connecticut, southern Rhode Island and parts of southeastern Massachusetts, including Boston. Parts of the Mid-Atlantic and Northeast, including Philadelphia, Baltimore and Washington, D.C., were under winter storm watches.

The menacing forecast comes less than two weeks after February wrapped up as the nation's second warmest since climate tracking became a thing in 1895. But days of bitter cold, with more to come, doesn't bode well for the confused flowers that had prematurely emerged on trees and plants across much of the region.

During the brunt of the storm, northeasterly winds will pull ocean water toward the coast and create rough surf from Virginia to Maine, Accuweather predicted, leading to tides 1-2 feet above normal. Coastal flooding and beach erosion are also a concern.

The storm was billed as a potential nor'easter — brutal storms that form along the East Coast as warm air from over the Atlantic Ocean clashes with arctic cold to the north and west. The storms get their name from the northeasterly winds that blow in from the ocean ahead of the storm.

“We are closely monitoring this storm as it develops and I am directing all state agencies to be on alert and ready to respond as the weather develops," New York Gov. Andrew Cuomo said. He promised that more than 2,000 trucks and 443,000 tons of road salt were at the ready.

Most of the region will be dealing with extremely cold temperatures until the weekend, so don't look for a quick melt, Kines said. Even though the big storm, if it materializes, would hit just a week before spring officially arrives.

"The fact that it is snowing, that happens this late," Kines said. "When you start talking a foot of snow or more, that doesn't happen very often."

Includes reporting by John Bacon and Bart Jansen of USA Today.