Forecast Discussion for May 20, 2010

As you can see on the WV imagery, the lead s/w trough that brought us the rainy weather is now heading out, NEward as it treks through New England. Another one is dropping southward over the area this morning. This has kept the low clouds in the picture for most of the overnight, and into the early morning hours. Regional observations show a few showers, relatively weak and scattered about, so it clip the western portions of the forecast area. Latest surface analysis shows weak low pressure moving out over Maine, and a surface ridge over the OH Valley. Both these features are very weak, so there is no pressure gradient between the two. A cold front front is movig down from Canada as well.

We'll begin to lose the clouds throughout the morning, as the s/w trough treks out. I'll go for mostly sunny skies by the early afternoon. The cold front will continue to trek southward, and a pre-frontal trough will develop out ahead of it. They'll be a few showers/thunderstorms, as indicated on a few short-range models such as the WRF. These showers should die out with the loss of daytime heating as they head southward with the front. So pops around 20% will be put into the grids.

As the s/w trough moves out with its associated cool pool aloft, temps at 850mb will begin to rise. We'll see temps between 10 and 12'C, which correlates to temperatures around 80 degrees or so. Afternoon seabreezes will be had at the coast, with an onshore flow ahead of the cold front, so temps there will be cooler.

Any showers or isolated thunderstorms will die out with the loss of heating. The cold front will run into the surface high that is building to our west, and should wash out with time. Temps will fall into the mid 60's in the urban corridor, Winds decouple over the interior, with decent radiational cooling conditions expected, with lows in the 50's as the airmas behind the washing out front is not all that cooler.