Forecast for Sunday, December 9, 2012

A nearly stationary frontal boundary should move southward this evening as a weak cold front. There is some question as to how far south this front moves and thus how far the drier air can puncture into our region. In areas where drier air fails to make much progress, overcast skies with patchy fog is a possibility for much of the night. I think it is best to forecast mostly cloudy skies for now with areas of patchy fog. The most breaks in the clouds should be found in the Poconos.

The weak cold front puts on the brakes sometime Sunday Morning. North of the front, there maybe a few breaks early in the clouds with peaks of sun. Meanwhile, closer to the front in our southern areas, it will be mostly cloudy and there could be a few rain showers. Then the front will begin to reverse itself and return northward as a warm front later Sunday. This will likely mean any breaks of sun will be limited to a few hours and these breaks should diminish later in the day. Rain should also develop by evening with overrunning precipitation (warm air riding over the colder air) occurring. Those peaks of sun in the northern areas, if they occur, could make for warmer late morning and afternoon temperatures across the north. However, the southern areas will actually end up with higher maximum temperatures for the day because warmer air will move in from the south late Sunday Night and the southern areas may fall south of the warm front or within the warm sector by late Sunday Night. This means the southern half of our region could see rising temperatures Sunday Evening and highs after 11 PM. It is a very tricky forecast for Sunday temperatures and there is the potential for a bust.

On Monday, the warm front continues slowly moving northward. Yet again, we find ourselves trying to figure out how far north this front actually gets. It may very well have a tough time moving north of the Poconos and Lehigh Valley. South of the warm front, mid-sixties to low-seventies is a possibility with some sunshine. North of the front, it will be showery, overcast, and foggy with temperatures holding in the upper forties to mid-fifties. A cold front is expected to arrive late Monday into Tuesday Morning. Widespread rain showers are likely with even a few thunderstorms. The best chance of thunderstorms will be in the areas that see warmer maximum temperatures on Monday which may allow for some modest instability and CAPE values to build up.

After Tuesday, it turns cool again with mostly sunny conditions. The next system may arrive next weekend with a chance of precipitation. For more on our long term trends, see the previous post.