Wednesday, July 31, 2013

Philly's Rainfall An Exceptional Regional Exception

If one were to look at just Philadelphia for rainfall this month and think that were the total of the whole of the Mid Atlantic or even Delaware Valley, they'd be mistaken. Eight inches of rain in a localized area, with a swath of four inch plus rains occurring along a 20 mile swath from Wilmington northeast through Cherry Hill, does not a regional rainfall total make.  Neither does six inches, which fell a week ago Monday, across Burlington County in Mount Holly and Mount Laurel.

As evidenced by the rainfall gradient across the city on Sunday's event, not everyone has been blasted with ark-busting rainfall. Here in my suburban perch, ten to fifteen minutes of rain yielded a couple of hours of sun while those storms created lakes along Route 42 and Route 130 in South Jersey.

For the month, Philadelphia's total is rather anomalous compared to the region's totals.

The majority of the region is running above average on rainfall -- exceptions include Atlantic City, Allentown, and Wilmington -- but the percent to normal for everyone else is within the realm of what's considered reasonable, within a couple of inches of normal on either side for just about everyone.

Even drilling down closer, the rainfall at the Airport is not representative of what's fallen in the city.  Northeast Philadelphia this month has picked up 4.07" of rain, less than a third of what the Airport has received. Millville, located between Atlantic City and Wilmington, has over five inches of rain this month and is running a bit above average.

Rainfall distribution is rarely uniform, with some locations often out-performing others. In summer, when steering mechanisms are a bit weaker and training (storms tracking in similar general path) is more apt to occur, incidents such as Sunday can skew the reality of rainfall for a location. While the record books will remember 8.02" of rain on Sunday and 13.24" for July 2013, your yard in Eagleville, Bensalem, or Allentown knows differently as it didn't get anywhere near that!