Monday, July 29, 2013

Yesterday's Record Setter Was Localized

To give you an idea of how localized yesterday's excessive rains (for some) were, twenty miles separated just under two-thirds of an inch of rain at Northeast Philadelphia between over eight inches of rain at Philadelphia International Airport.  Yesterday's 8.02" total at PHL set a daily rainfall record for any day, any month.

It's not like it didn't rain anywhere else -- some parts of the region picked up close to an inch such as Pottstown and Limerick, others picked up a solid half inch of rain (Trenton and the Northeast).  However, the stripes of real estate across South Jersey, the southeastern half of Philadelphia, and down into Wilmington were the "winners" in the rainfall game as training set up shop and ran over the same real estate.

There were two rounds of "training" that set up yesterday -- the first between 3 and 8 PM along I-95 and I-295 -- that round lead to the lake along the 42 Freeway (er, I-76) in South Jersey just above I-295 as well as to numerous reports of flooding along Route 130 in South Jersey.  That round of training produced the following HOURLY rainfall totals in Philadelphia:

  • 2.56" from 3-4 PM (this is pretty close to a record if not in fact a record for any hour in Philadelphia...hourly records are a lot harder to pin down)
  • 1.82" from 4-5 PM
  • 1.57" from 5-6 PM
  • 1.40" from 6-7 PM

Any of those totals are impressive on their own -- but in four successive hours, flooding is going to be a problem (and there was enough of that to go around).

Those of you above I-95 were largely scratching your heads, wondering what the fuss was about. Northeast Philly picked up less than an inch of rain, Mount Airy picked up just a few tenths.  Rainfall largely set up and stalled along the same general boundary, which is known as training because precipitation tracks along the same path largely like trains.

The first train ran between 3 and 8 PM along a swath from Wilmington northeast to Cherry Hilly, centered around the Airport, Gloucester City and Camden.  A second train set up between 9 PM and Midnight farther south, generally from Smyrna in Delaware northeast through Glassboro where another couple of inches of rain fell.

(More: Radar loop of yesterday's storms -- via wunderground)

These rains weren't it for Philadelphia, a late night party of thunderstorms came through the city and parts of the suburbs between 1 and 3 AM, bringing another couple of tenths of an inch of rain that propped our monthly rainfall total up to 13.24" (as of 5 AM), which is the second wettest month on record and wettest July on record. It trails only August 2011 in the great rainfall chase...and that record ain't going to fall in the next three days. Unlike August the other months on that list, this month's run into the record books is much more localized in nature as Atlantic City's total rainfall in July is 3.40", Trenton's is 5.44"...both significantly lower than what's fallen at the Airport.

We've picked up 23.77" of rain in the last two months at the Airport -- nearly TWO FEET of water. Granted, the August/September 2011 duo was a bit higher as we nearly dropped thirty inches of rain but such totals are still very impressive regardless of past precedent.

Rainfall Totals (NWS, as of 4:30 AM Monday)