Monday, June 25, 2012

Worst Three Day Heat Waves In Philly History

The heat wave that ended on Friday featured three consecutive highs of 95 degrees or higher...definitely a legit, honest-to-goodness heat wave.  This wasn't a cheapy shot of heat and modest humidity, it was one of those old fashioned summer heat waves that did a number on local roads and drenched us in sweat.

In terms of three day heat waves, it was also one of the most intense.  Our Heat Wave Index (HWX for short) was developed to measure the cumulative impact of heat over a stretch of 90 degree days.  Our index takes the daily progressive heat impact (the measure of intensity, duration, shock value, and overnight lows) and combines that over the run of a heat wave to give us a measure of how "bad" the heat really was.

The HWX that this most recent heat wave ended up measuring was 48 -- which would rank tied for 6th all time among heat waves of merely three days (no more, no less).  It was also the most intense three day heat wave since one hit the region between June 15th and 17th, 1991 -- when the mercury reached 98, 100, and 94 over the course of those three days.  The worst of the three day heat waves was an event that scorched the region in June, 1952.  Between June 25th and 27th, the thermometer topped 98, 100, and 95 over the three days, with lows only bottoming out at 80 on June 26th.   What makes the June 1952 heat wave a bigger slap in the face was that on June 21st-23rd, highs were 67, 67, and 64 degrees.  Temperatures jumped to 86 on the 24th, then to 98 on the 25th.

Talk about a true shock to the system!

While this most recent heat wave did not bring a 100 degree day, it was certainly a noted change from the cool regime of a few days prior when temperatures were in the lower half of the 70's.