Track tonight's thunder on our current weather page.
Update, 8 PM: From a rather empty PPL Park as the storm rolled in on the Union match. This storm definitely packed a bite farther northwest of the city, as the Lehigh Valley and Berks County featured damaging winds and some hail. Locally, though, the storm is bringing better shots of "doomsday" cloud decks, wind, and a refreshing temperature drop of nearly 20 degrees in some spots. However, the storm line weakened as it moved into Philadelphia from the west thanks to diminishing instability with the loss of daytime heating and less potent dynamics that were found to the north and west. Downpours and occasional gusty winds will continue off and on through the evening hours as the storm line moves through the region.
Update, 7 PM: Severe thunderstorm warnings have been issued for the upper half of Chester, Montco, and Bucks until 7:45. Storms are now entering the western portion of Chester County and are moving east and northeast...we should see conditions deteriorate across the burbs over the next 30-45 minutes with storms moving in. Wind is the biggest threat for now with these storms but hail and heavy rains will accompany as they move in. Many locations could pick up a quick inch or two of rain over the duration of the storm.
Update, 6 PM: A severe thunderstorm watch was issued recently for Southeast PA and the northern two-thirds of New Jersey until 10 PM. This watch is for the counties in pink or the hybrid of pink and green shading. A flash flood watch is out for the green county and hybrid pink/green shading through tonight. As of 7 PM, the line of storms extends from Mount Pocono to Lehighton to just west of Reading to York. Cells are moving northeast on an eastward moving line. Probably will see the arrival time for these storms a bit earlier than what is listed below...but not significantly earlier...but they should get to Philly by 9 PM.
Approaching 5 PM and the line of storms is really taking off...extending from near Scranton to Harrisburg to Hagerstown, moving east-northeast. The worst of the line is generally in two pockets -- one to the west of Scranton, the second to the west of Harrisburg. That southern "bad" pocket is what will move through the northern suburbs and the Lehigh Valley over the next few hours.
The city's activity looks to be produced from cells that are to the south of Hagerstown, MD, at this point. The line in Maryland and in Northwest Virginia is still potent but not on the order of what is working through Central Pennsylvania this afternoon. That said, the storms could produce frequent lightning, gusty winds, and heavy rainfall. A flash flood watch is out for tonight for Eastern Pennsylvania and New Castle County in Delaware. Heavy rainfall in localized areas could reach two inches or more -- that's enough to cause flooding in streams that were hit pretty hard by last weekend's pop up and slow-moving thunderstorms in Eastern Pennsylvania. Not everyone will get two inches of rain but the best chances for it will be west and northwest of the city this evening with the strongest of thunderstorms.
A severe thunderstorm watch is also out for Lehigh, Berks, Lancaster Counties and the Poconos until 9 PM.
Timing this system out, it looks like Reading could get in on thunder after 6 PM, Allentown by 6:30-7, the western suburbs around 7:30-8, and Philly around 9 PM...give or take. Evening activities in the city should be ok -- it's north and west that might have some issues especially after 6 PM and towards sunset as these storms approach. Jersey and Delaware should be OK this evening...storm chances do increase after sunset from the west but with the setting sun storms will not be as strong as they are now in Central PA.