The squall that shredded a quiet Washington Sunday afternoon and left capsized sailors battling hypothermia in the cold Potomac was a freak of nature that came so fast that weather forecasters had no chance to warn area boaters, the forecasters said yesterday.

The National Weather Service didn't get out a marine warning until 18 minutes after the 50-knot winds struck Washington at 3:27 p.m. The sudden storm capsized at least 40 craft on the Potomac, with one boater listed as missing and presumed dead yesterday.

"It was a freak because it intensified so suddenly," said Joe Bocchieri of the service's forecast office.

Forecasters said the storm was caused by an unusually cold air mass suddenly moving into an area that was experiencing sunny, mild weather.

The freakish April weather continued yesterday and last night as yet another fast-moving storm dropped up to eight inches of snow on parts of Southwestern Virginia and as much as four inches in the Tidewater area.

The National Weather Service said the storm would stay well south and east of Washington, however, and that area residents could expect today to be cloudy and breezy with a possibility of snow flurries.

Washington Sailing Marina officials said yesterday that damages to boats in the area near National Airport, where most of the capsizings occurred, would total $7,000 to $10,000, mostly from broken masts and torn sails.

All abandoned boats had been retrieved by late yesterday, according to marina officials.

"There wasn't anything you could look at to see it was coming," said James Dillard of Fairfax, a member of the Virginia House of Delegates who was racing his small boat off National Airport Sunday.

"I've been sailing here since 1959 and I'd never seen anything like it," Dillard said after he returned to land.

Veteran Potomac boaters expect sudden squalls on warm summer afternoons, when great thunderheads roll in from the west. But they are more predictable because normally there is not such a drastic difference in temperature between the storm moving into an area and the air mass already there, forecasters said.

Sunday's storm was also particularly dangerous because of the 50-degree water temperature, harbor police said.

Maryland marine police continued the search yesterday for Hung Wang, 35, a Department of Energy economist who has been missing since he was thrown from a sailboat floundering in heavy waves on the Potomac Sunday.

Wang, of 900 24th St. NW, was trying to retrieve a stray line on a 21-foot Explorer class sailboat when the boat suddenly pitched, according to friends.

Robert Rafloski, a friend of Wang, said Wang and two friends rented a boat at the Fort Washington Marina and had sailed for several hours when the unexpected storm knocked loose the jib sheet, a line that controls the front sail.

Wang crawled onto the bow of the sailboat to try to retrieve it and was swept overboard when another heavy gust of wind tilted the boat suddenly.

One of Wang's sailing companions, Earl Williamson, put on two life jackets and dived in to try to reach Wang, who had no life jacket, but after several times coming within a few feet of him eventually lost sight of him in the heavy waves, Rafloski and marine officals said.

A colleague of Wang's, Harold Mohr, said yesterday that Wang had little sailing experience, but had been boating recently in preparation to buy a sailboat.

Dillard's boat capsized along with perhaps two dozen other Sunday racers from the Potomac River Sailing Association just below National Airport. D.C. Harbor Police said 33 boats were overturned in D.C. waters above Wilson Bridge.

Gioia Blix, making rescue runs on Washington Sailing Marina's 17-foot Boston Whaler, brought in 25 boaters. "I did people," she said. "Forget the boats."

Some boat owners were hard to convince. "A lot of them were incoherent," she said.

"They didn't want to leave their boats. It was frustrating. I figured if I left them, we might never see them again."

By the time the storm had crossed to the Chesapeake Bay the Weather Service had issued a marine warning and daylight was running out.

Few boats were sailing when the squall touched down there about 5 p.m.

Although a number of boats had to be assisted to shore, officials reported no injuries to sailors and no damage to boats in the bay.