Boston weather forecast 8/20/11: some sun, possible shower/t-storm

This is a new forecast, starting Friday evening.

Forecast Discussion: A weak cold front is starting to develop some severe thunderstorms over the city of Boston. A Severe Thunderstorm Warning is now in effect for the city until 3:45 PM. This front will pass early tomorrow morning. There is the slight chance for a shower or thunderstorm before midnight, then it will remain partly to mostly cloudy. By tomorrow, some isolated showers and thunderstorms may form in the late afternoon or early evening. However, I would not call this day a washout. Beaches should see highs in the upper 70’s to lower 80’s. A weak high pressure ridge will give us drier conditions on Saturday night. But, another cold front in the Northern Plains will move over us by late Sunday afternoon. This front, along with high humidity, will produce isolated areas of heavy rain and strong to isolated severe thunderstorms. The precipitation will end as the front moves offshore Monday afternoon. High pressure will bring drier weather by midweek. But, a new cold front will bring showers and periods of rain Thursday night into Friday afternoon.