This time of year, Irondequoit Bay normally is one huge sheet of ice and Dean Rudy is careening down the ski slopes. Instead, he's been zigzagging on water skis in sunny, 50-degree weather.

"It's absolutely delightful. I already feel like I've cheated winter," the 34-year-old Xerox Corp. manager said. His wife, Merilou, was at the controls of the boat on Tuesday, and their two children were along for the ride.The mild weather, extending through the fall and into the first week of winter, is proving a boon for golfers, roller skaters and hikers in the Northeast and Midwest, and a headache for winter clothing retailers, ski resorts and ice fishermen.

Also mighty peeved in usually frosty New York City is Rabbi Abraham Abraham, a.k.a. "The Mighty Atom," who is president of the Coney Island Ice-Breakers Winter Ocean Swimmers.

"I just got off the beach swimming," he said. "Normally, the temperature of the water is in the 30s. Now, it feels like it's in the 50s. It did not touch my vibes, give me that heavenly feeling."

November was the fifth warmest in a century in the Northeast, with temperatures averaging 3.6 degrees above normal, and "there seems little doubt that December will prove to be another mild month," said Warren Knapp, director of the Northeast Regional Climate Center at Cornell University.

In the Berkshires over the Christmas holidays, skiers were hitting the slopes at night, leaving daytime for more warm-weather sports, said Larry Dubin of Jiminy Peak ski resort in Hancock, Mass. He estimated business is down at least 15 percent.

Other ski resorts, outfitted with snowmaking machines, said their trails are probably as full as ever.

"If anything, warmer weather brings more people out," said Timothy McAtee, who owns a resort in Watertown in northern New York. "Besides, manmade snow is more durable."

Resorts make snow at night, when the temperature drops below freezing, and build up the trails enough so that they can last the day without melting away.

In the Adirondacks, 500 miles of snowmobile trails have almost melted away in Webb, N.Y. "More than half of what we expected (in reservations) have been canceled," moaned the town's publicity director, Bob Hall.