Wednesday, August 28, 2013

Let's Just Scrap That "Smattering" Talk

Granted, not everyone was rained upon today. The Shore above Atlantic City dodged a lot of the rain today, and areas south and southwest of Wilmington dodged a fair amount of rainfall as well.  However, in between those two locations, varying amounts of rain fact, some spots picked up close to three inches through 5 PM today (see below).

The city's 0.97" as of 5 PM puts them to 29.64" since June 1st, which is the rainiest summer ever...even including the unofficial era before 1870.

The heaviest rains today were in a stripe that extended from Allentown south through the western half of the city -- North Philly had an unofficial report over two inches on our Facebook page, with one inch totals across Bucks, parts of Montgomery County, on south into South Jersey.

The cause for this um, ugly bust, in our forecast was a convergence zone (boundary that caused moisture in the atmosphere to lift and squeeze out) that stretched across Eastern Pennsylvania into South Jersey. These mesoscale features are hard to pin down in modeling -- and often times short term modeling struggles to pick this up.  While the NAM and HRRR (the HRRR is a pretty reliable piece of guidance) hinted at steadier showers to our west and southwest, the SREF (which I didn't rely on in our forecast as it was a bit of an outlier in precip intensity and amount) had those showers much closer to the region.  Other models were less robust in the amount of rain that was projected -- GFS and Euro generally in the quarter to half inch range.

Had this set up 50 miles to our west, I wouldn't be miffed about our forecast and it would have played out pretty well. Not great, but tolerable.

Boundaries matter and small scale features matter when there's a moisture rich environment, which we had today with PWAT's pushing two inches out there.  These heavy mesoscale rains have been proven time and time again this summer (see the eight inch rain in Philly a month ago).