A snowfall that brought huge drifts and closed roads in the Buffalo area finally ended Friday as the looming threat of rain and higher temperatures through the weekend and beyond raised the possibility of floods and more roofs collapsing under the heavy loads.

More than 30 major roof collapses, most involving farm and flat-roof buildings, were reported overnight, officials said Friday, after snow Thursday brought the Buffalo area's three-day total to an epic two metres or more.

The forecast called for a chance of rain on Saturday and more through Monday, along with temperatures of about 15 C.

The U.S. National Weather Service issued a flood watch for Sunday through Wednesday, and meteorologist Jon Hitchcock said there might be trouble with drainage as snow and the uncollected autumn leaves underneath blocked catch basins.

New York snow

Michael Palmer and Carin Schultz work to clear her car of snow and remove it from Union street in the suburb of Hamburg, Buffalo, New York. (John Normile/Getty Images)

As towns and villages began preparing for potential flooding, stir-crazy homeowners — some stuck inside since Tuesday — and store employees around the region climbed onto roofs to shovel off the snow and reduce the danger of collapse.

"Five hours yesterday and that's just the beginning," John Normile said Friday of the effort to clear snow from the roof of his Lake View ranch-style home. He, along with his daughter and her boyfriend, had knocked about 180 cm off the back of the house and planned to be back at it for a second day.

"We're getting really concerned about the weight of it," Normile said. "We've got to do it before the rain comes."

12 deaths

The storms were blamed for at least 12 deaths in western New York, mostly from heart attacks and exposure. The latest was a 50-year-old man was found Friday morning in his car, which was buried in snow in Cheektowaga, police said. The cause of death wasn't immediately known.

One elderly resident of a nursing home died after it was evacuated amid concerns of a roof collapse, a spokeswoman for the home said. Deputy Erie County Executive Richard Tobe had earlier reported two deaths in the evacuation.

"We know that relocating people from nursing homes is a very tough thing to do," Tobe said.

More than 50 people were evacuated from several mobile home parks in suburban Cheektowaga and West Seneca on Thursday because roofs were buckling. Tobe said at least 90 small roof collapses involving carports and other structures had been reported by Friday morning, in addition to damage to a pharmacy and a metal warehouse operated by a Christmas decorations company, where damage was estimated in the millions.

Some farm animals had been injured in damaged barns, he said.

With roads impassable, driving bans in effect and the Buffalo Bills' stadium buried in snow, the NFL decided to move the Bills' Sunday home game against the New York Jets to Monday night in Detroit.

463 plows

National Guardsmen drove nurses to their hospital shifts. State troopers helped elderly residents trapped in their homes. State officials assembled 463 plows, 129 loaders and 40 dump trucks from across the state for a massive cleanup effort.

Some Buffalo-area schools were closed for the fourth day, burning through snow days with winter still a month away.

A 212-km stretch of the Thruway, closed since Tuesday, opened mid-afternoon, with some restrictions.

Wintry Weather

Dump trucks wait Friday at the Central Terminal to dump snow removed from south Buffalo neighbourhoods after heavy lake-effect snowstorms. (Mike Groll/Associated Press)

Exit ramps will remain closed along the westernmost 193 kilometres, so, "Assume if you get on headed west you can't get off until Pennsylvania," Gov. Andrew Cuomo said, noting that roads remain "very dangerous."

With deliveries interrupted, some grocery stores reported running low on staples like bread and milk.

"No matter how you cut it, this event will end up in the top five for the Lake Erie area," said U.S. National Weather Service Director Louis Uccellini.

Worst flooding expected Monday

Cities and towns were positioning pumps and other equipment in anticipation of widespread flooding. The worst is expected Monday when, with temperatures at or above 15 C, snow is expected to melt faster than it can be absorbed by the ground or snowpack.

"There's roughly the equivalent of six inches (15 cm) of rain in the snowpack that will essentially be released over two days," Tobe said. "If it was released as rain it would be a monumental storm."

But flooding will likely affect mostly basements and creeks, he said. "It's not going to be this giant flooding like you see in hurricanes," he said.

USA-WEATHER/

TJ Zydel works to clear his roof in the town of West Seneca near Buffalo Thursday. (Lindsay DeDario/Reuters)

Because the Buffalo area is so snowy, building codes require homes and businesses to be able to handle up to 50 pounds per square foot on their roofs, which would be about as heavy as a slab of concrete 10 cm thick, according to Mark Bajorek, a structural engineer.

As anyone who has ever shovelled snow knows, its weight depends in part on how wet or fluffy it is, not just on how deep it is. But Bajorek said some buildings may be close to that limit now, with more precipitation on the way.

Engineers were expected to be out Friday trying to determine how much water was in the snowpack.