Sunday, July 24, 2011

Nastiest Day Since 1995

I was up in Upstate New York for a couple of days...thinking initially I would dodge the worst of the heat that was gripping the Delaware Valley on Friday. Unfortunately, my heat waterloo was in Watkins Glen, NY on Thursday where a bank thermometer topped out at 105 degrees at 5:30 PM.   While it was a touch aggressive, the high of 104 just 20 miles south in Elmira wasn't.   It was nasty up there Thursday and while still hot on both Friday and Saturday, the heat was much more tolerable as dew point levels were in the 50's and low 60's.   Jumping into Seneca and Cayuga Lakes was arguably more of a relief on Friday and Saturday.

The heat waterloo for the Delaware Valley was arguably Friday -- widespread heat index values of 110-120 gripped the region during the worst of the heat as the region baked in air temperatures of over 100 degrees, with heat index values of over 110 at peak heat as dew point values were in the 70's for much of the day in much of the region.   The record winner among observation sites locally was Wilmington, with a heat index of 123 at 3 PM.

This was arguably the worst day in the region from a heat and humidity standpoint since July 15th, 1995 -- a date that lives in heat infamy in Philadelphia as the heat index topped out at a sweltering 129 at the worst of the day.  In terms of hourly heat index values, the worst Philadelphia experienced on Friday was 118  (3 PM, temp of 102, dew point of 77).  You can see the '95 heat index values in orange on the far right compared to this past Friday...'95's dew points were several degrees higher which made the heat index run 120 or above from late morning through the 7 PM ob.   If you notice the humidity levels in the 40's and 50's, on a "normal" summer day those readings aren't so bad but on a very hot day 40-50% humidity is excessive.   This is why using dew point in concert with temperature is a much more effective way to measure the "nasty" factor.

The good news is that we should likely not see any more days as extreme as this during the remaining weeks of this summer.   Heat will still be an issue as well the muggies but no attempted repeats of July 1995 are on the horizon.