That's one big high-pressure system settling over the eastern United States (see map). By this afternoon it will stretch from Texas to Maine. The high brings clearing skies today and diminishing winds after sunset. And that should mean some serious cooling tonight.

The National Weather Service's Sterling forecast office is predicting a low of 40 degrees tonight at Baltimore-Washington International Thurgood Marshall Airport. Patchy frost is possible in the usual cold spots west of the I-95 corridor. Frost advisories and a freeze warning are posted for parts of the state tonight, from Hagerstown west.

A plunge toward 40 would threaten to tie the record low for a May 19 by morning. The record low for a May 19 in Baltimore is 39 degrees, set on that date way back in 2003.

But with the high moving in from the Ohio Valley today, skies will be clearing, and the high May sun will start to warm things up. We may only get to the mid-60s today - still about 10 degrees below the long-term average for this time of year. But the high, and the sunshine, will stick around all week, driving temperatures well above average by Wednesday, with highs near 80 degrees Wednesday through Friday.

But, as luck would have it, unsettled weather is forecast to return by the Memorial Day weekend. Our fate rests with low pressure that's expected to develop over the Gulf Coast. If that low starts sending moisture up the East Coast as the old high moves out this weekend, we would get several days with 30 percent chances for showers and thunderstorms.

Sunny, pleasant workdays, and a showery holiday weekend. Figures.