Thursday, July 19, 2012

Update on Rains Tonight & Tomorrow

Radar at 4 PM shows a pretty decent line of storms back across Western PA, a few hours away from hitting the Philly metro but it continues to slowly march east.  Other scattered storms have popped along the frontal boundary across Southern Pennsylvania, Delaware, and South Jersey.  All of these are moving slowly east and southeast, with the line back to the west generally moving east.

The tricky part of this forecast is how that line works into our relatively "stable" airmass overhead.  With the "cool" front lying just south of the region we're in a semi-stable airmass despite a surplus of humidity and a downright muggy afternoon around here.  It feels more like Miami than Montreal despite being behind the cool front as dew points are all in the 60's and lower 70's.  There's enough 'there' from a moisture standpoint for rain at some point tonight but seeing a widespread thunder threat along the lines of what's churning through Western Pennsylvania remains to be seen.   We may see a bit of a fizzle in rainfall as these storms move in thanks to that stable boundary in the atmosphere overhead while they tend to survive (if not thrive) down across Delaware and South Jersey later on.  The NAM (below) shows that scenario playing out.  That said, these storms have done a good job surviving through Pennsylvania so far so it is more than possible we get something out of them when they move through later on.  Best chances for rain, though, will be generally from the city on south with this evening's storms.

Farther west, mid level energy lurks in Michigan and is moving east.  This should wrap up over Pennsylvania and result in a rainier late night and Friday.  You can see the batch of rain moving into PA on the NAM graphic above later tonight...this should get into our region on Friday morning and result in an at-times rainy Friday around most of the region.  Given this is mid level energy we would be working with, parts of the region could get less rain than others while some parts of the region could see over an inch of rain between tonight and tomorrow.

Rains will be moderate and according to the NAM and Euro computer models, focused more substantially on areas north of the city than south.  So, following that logic tonight may be more city and south with tomorrow being a rain event that mainly focuses on the city and points north.  The potential according to the Euro is for over an inch from about Wilmington to Atlantic City on north, with potentially two inches of rainfall in spots. We'll see....we've been quite dry of late.  We may not get to those higher totals but an inch of needed rain certainly can't be ruled out.

Even if the steadier rains don't materialize south of town there is the potential for strong thunderstorms tomorrow south of Philadelphia -- a slight risk for severe weather is out for Delaware and extreme southern New Jersey for the potential for strong winds within any thunderstorm that fires tomorrow.

As always, you can keep track of the rains on our Current Weather Page and we'll have another update in the morning on where things are at.