P.M. T-Storms & Forecast for Sunday, June 12, 2011

Once again, we have decided to release our daily forecast earlier than normal today. There have been a few changes to our forecast today. The Storm Prediction Center has now placed most of our region under a slight risk for severe thunderstorms with the northeastern areas under a 5% or “see text” risk of severe thunderstorms.

The warm front moving through our region will be responsible for numerous showers and thunderstorms, especially across Southeastern and Central Pennsylvania into Delaware by mid-afternoon into early this evening. While I don’t like to live model by model run, as it can do you in, the 12z North American Model shows explosive development across these areas. If the warm front can nudge northward and give portions of the area some sunshine for one to two hours…we could be looking at a pretty decent severe weather outbreak. Shear would be sufficient near the warm front for even a few isolated tornadoes. The National Weather Service is concerned the Pennsylvania and Maryland border could be a hot spot for this activity. Chester and Lancaster Counties certainly could be within the bull’s-eye.

The late morning guidance from the NAM also seems to be suggesting the potential for flash flooding with excessive rains within 6 hours or less. It is showing 3 to 4 inches of liquid within this time frame. Earlier thunderstorms from this morning were quite active with torrential rainfall. Lancaster County is already under a flash flood watch...Mount Holly WFO could follow through shortly.

Rain and thunderstorms will be scattered throughout late tonight, although some of the activity may diminish.

A cold front is expected to move through our region on Sunday Night. A pre-frontal trough of low pressure should affect our area Sunday Afternoon into Sunday Evening with potential effects from the actual cold front itself if the atmosphere has not been overturned. While (as of early this morning) we are not under a slight risk of severe thunderstorms in the Day 2 Convective Outlook, later outlooks could include our region in a risk as I feel there is enough shear for scattered instances of damaging winds and large hail.

High pressure builds in bringing us a tranquil period for the beginning of the new week with low humidity and pleasant temperatures. More humidity and another potential for showers and thunderstorms could arrive by mid to late week.