Friday, June 01, 2012

Severe Weather Odds Higher South & West of City

Points south and west of the city are in a slight risk for severe weather according to the Storm Prediction Center as a storm system moves into the region later today.  The graphic on the left shows the counties that are in the current slight risk (as of early this morning)...those counties are in the yellow shading and generally include Delaware, Chester, New Castle, and Gloucester for our immediate region.   The city and points north/east are not in a slight risk as of now.

The reason why a good chunk of us are NOT in a slight risk for severe weather this evening is because of timing with thunderstorms (this evening into overnight), the positioning of a surface warm front that will move into the region later on today (the warm front won't clear the city and put us in the best sector for instability), and surface wind trajectory (south to southeast off of the Atlantic).  Farther south and farther west, better instability and less ocean influence will help set up the potential for severe weather across South Central Pennsylvania on south.

We tend to think the best chances for severe weather will reside to our west and southwest today -- Harrisburg, Baltimore, Washington, the Delmarva all stand a good shot at getting some damaging winds, perhaps hail, even a tornado can't be ruled out this afternoon (west) and evening (south).  The Storm Prediction Center's outlook for severe weather suggests a 10% chance of a tornado this afternoon from York, PA, south through Virginia.

The potential for damaging winds also remains highest to our west and southwest...with a 30% chance of a wind gust over 60 miles per hour across the red shaded areas.

Storms will fire up across Ohio this afternoon and spread northeast and east into Pennsylvania, with our best chances for showers and storms locally after 8 PM (starting from west and spreading east).   Since these storms will not be as strong here as they were to the west, gusty winds may still be a factor but the bigger story with these storms will be heavy rainfall.  Some places, mostly north of the city, could pick up two inches of rain tonight.  While flooding shouldn't be an issue for most locations, some localized flooding is possible in the Poconos and Lehigh Valley where the ground is more saturated.  However, the heavier rainfall is not expected everywhere and there will be locations that pick up only a half inch or even less than that.