BUFFALO, N.Y. — After a three-day onslaught that dumped 7 feet of snow on the Buffalo area and killed at least 12 people, the sun came out, but so did predictions of flooding caused by rain and temperatures of up to 60 degrees.

Weather Service meteorologist Jon Hitchcock said there might be trouble with drainage as snow and uncollected autumn leaves blocked catch basins.

“The biggest flood threat would be on Monday when temperatures are at their warmest,” he said. “There could be general urban flooding.”

“There’s roughly the equivalent of six inches 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.”

He said flooding would likely affect mostly basements and creeks.

The National Weather Service issued a flood watch for Sunday to Wednesday.

“We are preparing now for more flooding than we’ve seen in a long, long time,” Gov. Andrew Cuomo said. He said the state was sending in pumps, boats, helicopters and high-axle vehicles that can operate in 4 to 5 feet of water.

“If we’re lucky we won’t need any of it,” he said. “But prepare for the worst and hope for the best.”

The snow remained a huge challenge. Officials were still urging people to put off nonessential travel so snow removal efforts could progress. Cuomo reopened a 132-mile stretch of the state Thruway that had been closed since Tuesday, but several exit ramps remained closed along the westernmost 75 miles.

“Assume if you get on headed west you can’t get off until Pennsylvania,” the governor said.

More than 30 major roof collapses, most involving farm and flat-roof buildings, were reported overnight, officials said Friday, and warm temperatures could make the snow even heavier.