Baltimore Grand Prix fans may see some showers or thunderstorms on Saturday or Sunday. But forecasters have become even more certain that Labor Day Monday will bring significant rain to the region as a low-pressure system begins to draw tropical moisture this way from the Gulf.

Baltimore Grand Prix racing events should will be completed by Sunday. But Monday is scheduled as a make-up day if Saturday or Sunday events are postponed by weather or some other issue. 

The wet weather on Monday will include moisture from what hurricane forecasters expect will become Tropical Storm Lee later on Friday. The slow-moving storm is loitering in the northern Gulf of Mexico, and is forecast to dump as much as 20 inches of rain on portions of the northern Gulf Coast. More on that in the next post.

The National Weather Service's regional forecast office in Sterling, Va. says there's a 30 percent chance for rain at BWI-Marshall Airport on Saturday, with showers and thunderstorms most likely to appear after 2 p.m., just as the main events at the Grand Prix are getting underway. Forecasters expect less than a tenth of an inch of rain, unless you happen to be under a thunderstorm.

Rain chances on Sunday are the same - 30 percent - and so are the expected accumulations and the timing. On Sunday night and Monday, however, the predicted rain chances jump to 60 percent, with "thunderstorms likely."

Later in the week, forecasters expect the region will begin to feel the direct effects of whatever is left of that Gulf Storm:

"Long range models suggest a plume of tropical moisture from what should be named Lee will stream across the mid-Atlantic from the middle of next week into next weekend. This, along with an offshore flow, could create a significant rainfall event for the region, particularly for east-facing ridges, such as the Blue Ridge."

(PHOTO: Mike Ehrman, Getty Images, March 2011)