Thursday, August 01, 2013

Flash Flood Watches For Chunk Of Region

Flash Flood Watches are out for a large chunk of the region today, generally along I-95 and points north and northwest, as the combination of southern rains and an approaching cool front from the west will tag team over our region and give us a one-two slap of rain and thunder through the course of the day. It does not appear to be an all day washout but the potential does exist for some prolific rainfall in some locations later on this morning and this afternoon.

Rains will progress through the region in two shots -- the first, associated with warm advection that pushes up from the southwest in the form of a warm front. Your usual overrunning type scenario brings this morning's rain event for the region.  As a cool front to the west approaches us later on today, the atmosphere further agitates and combines with the humid airmass that the warm surge brings to produce additional rain and thunder through the region.

Severe weather does not appear likely but steady to heavy rain does, especially if you are north and northwest of Philadelphia.  Three higher resolution models (the two shown below plus a third version we outlined in the daycast earlier) show the potential for two inches or more of rain in parts of Eastern Pennsylvania. One of the models is a bit more robust on that heavy rain than the other but you can see that it's not an equal opportunity flooder today -- the heavier rain risk does set up for Eastern Pennsylvania.

The other operational models -- GFS, Euro -- are not quite as aggressive on targeting Eastern Pennsylvania and while the operational NAM shows Eastern PA gets a bit more rain than the rest of the region, it's not as rainfall-happy as the higher resolution models are apt to be.  That said, there is a good bit of moisture in the atmosphere pushing northward with this warm surge this morning and the combination of that, and the trigger in the form of the approaching cool front from the west, will trigger thunderstorms that will produce localized heavy rains later on.  Perhaps not on the scale of the uber-aggressive high-res modeling but some spots probably yield two inches of rain today, perhaps more.

South Jersey looks to dodge the rainy bullseye, as do the Delaware Beaches, but it's not an "all clear" type of day down there. You will have storms -- just not on the order of what may fall west of the city later.

It appears we get a lull late in the afternoon into the early evening hours around Philly -- although more storms are still possible this evening as a frontal boundary approaches from the west -- but a large chunk of the modeling gives us a lull for a while towards the PM rush. Whether that occurs remains to be seen.

More: Current Weather Page