They've spent months training in every sort of weather for Wellstone's Dallas White Rock Marathon. But for the 15,000 runners racing Sunday morning, this is not exactly the forecast they want to hear: "A pretty good shot of rain."

But that's almost certainly what they'll get. Most will just shake it off.

"As long as it isn't lightning, it's a go," said Mike Windsor of Fort Worth, picking up his race credentials on a gorgeous Friday afternoon that felt more like May than December.

"We practice in every type of weather," said Lance Johnson, a member of the same training group, "so whatever it is, bring it on."

That's the spirit, because the Dallas area is in for a major change, with temperatures plunging from a record 84 on Friday afternoon to around 35 by Monday morning.

And it all begins Sunday, about the time the marathoners take their first steps, the first raindrops fall and the temperatures start to slide.

"I think it's going to be pretty wet," said Pete Delkus, chief meteorologist at WFAA-TV (Channel 8). "I think it will be steady rain in the afternoon, and more scattered in the morning."

The temperature at race time should be in the upper 60s, Mr. Delkus said, but that will be the peak, and it will slip through the day as the rain increases.

Dan Shoemaker, a meteorologist with the National Weather Service in Fort Worth, put the chance of rain Sunday at 70 percent, tapering to 60 percent Sunday night, with sharply cooler temperatures by Monday morning.

The warmth will be gone, but the wet remains, perhaps into Wednesday, Mr. Shoemaker said.

That's a world of difference from the weekend's start. Friday's 84 degrees broke an 85-year-old record for the date, and today's forecast high of around 80 could be a record, too, forecasters said.

Of course, that isn't exactly ideal marathon weather, either. But anyone tackling a 26-mile run doesn't worry too much about the weather.

"The first [White Rock] Marathon I ran 11 years ago, it was freezing at the start, started raining as we were running around the lake, and in the end was like running in a carwash," said Fort Worth runner Debbie Koennecke.

"After all the work we've done," said Mr. Windsor, who's running his first marathon, "it would have to be really bad to keep me from running."

Fortunately, it probably won't be really bad when the marathon begins at 8 a.m. Sunday near American Airlines Center.

Besides, runners are an adaptable bunch.

"I don't like the rain much," said Frank Douglas of Forney, but it won't stop him.

So what preparations will he make should the skies open?

"I'll put on my hat."