Severe weather looks like a distinct possibility for a chunk of the region tomorrow, with a moderate risk of severe weather out from Lancaster to Quakertown to Trenton to Toms River and points south, with a slight risk for areas north of that. The difference between slight and moderate in this case will likely do with the track of a low pressure center and disturbance across the region during the afternoon and evening hours and the amount of clearing that can take place after the leftovers of today's likely severe weather outbreak in the Midwest (we'll get the weakened leftovers late tonight in parts of the region). The red shading is the moderate risk area, yellow shading is slight.
The Storm Prediction Center indicates a 45% shot at severe weather within 25 miles of a point tomorrow afternoon and evening in the purple shaded areas -- pretty much a coin flip chance. Odds are lower to the north. The area within the black line is where a ten percent chance of significant severe weather (EF-2 tornado or stronger, wind gusts from severe weather of 75 mph or higher).
With the severe weather events in the Midwest later today, modeling suggests the weakening remnants of the storm complex push east into our region late tonight as rain and thunder, riding east along the stalled front to our south (today) that lifts back north (tonight). Whatever is left of that complex of thunderstorms moves through the northern half of the region late tonight and early tomorrow (NAM modeling below shows the hint of it after 3 AM). The morning shower/storm threat will gradually lift north with the warm front, putting Southeast Pennsylvania, South Jersey, and Delaware under the gun for strong and severe weather with thunderstorms that develop to our west in the afternoon hours.
Severe weather looks most likely after 3 PM to our west, after 5 PM in the city, and after 6 PM at the Shore. This is a rather robust disturbance that is modeled to push through -- the energy aloft and the amount of dynamics associated with the low pressure center are such that a severe weather outbreak is certainly possible.
The keys in this event occurring are placement of the warm front boundary -- areas south of the boundary will stand a much greater shot of getting severe storms, as well as how much sunshine breaks out in the warm sector as sunshine will destabilize the atmosphere.
In addition to the severe weather potential, the threat for heavy rains do exist tomorrow across the entire region, with areas to the north more prone to a consistent, persistent heavy rain event. Flood watches are out for much of the region for tomorrow.
Modeling does suggest the prospect of one to two inches of rain from thunderstorms in the region. If the severe aspect of these storms verifies out, a good chunk of that may fall in a short period of time, leading to more flooding problems. If your side street, stream, or parking lot flooded on Monday, it has a pretty decent shot of doing so again on Thursday.