Tuesday, June 19, 2012

Two Day Heat Events

While not as lengthy or painful in duration as dog day heat waves in July and August -- the type of heat wave that can last for several days or more, the two day heat event can sometimes bring heat that rivals those found in those longer duration heat wave patterns.  While the Delaware Valley has sweated through three 100 degree days the past two years, those have been in the more "typical" long duration heat wave that lasts multiple days.

With the possibility of the upcoming heat event dodging a high of 90 degrees on Friday (and thus avoiding the textbook definition of heat wave), we went back through the record book to look at the hottest days in a two day heat event where the high in consecutive days was 90 or above...but not for three or more days.

Going back to the start of "modern" data in Philadelphia in the 1870's, we've had four instances where a two day heat event has produced a 100 degree high...two of which from a singular event in 1988 (July 10th and 11th).  The 1988 event deserves a bit of an asterisk because there were two "cool" days with some showers that preceded and succeeded the back-to-back 100's...and the 100 degree days were part of a 16 day in 18 stretch where temperatures broke 90 or higher...it just happened to be a two day spike sandwiched in between those two sub 90 days.  Regardless, it counts as part of the data set because there was no "heat wave" in the three day cycle.  

The other two events, 1934 and 1954, were legit two day heat events.

Considering it's been almost 25 years since the last time we even got into the upper 90's as part of a two day heat event, it's not terribly easy to spike in short duration and somehow avoid getting a three day streak of 90 degree weather.   However, history has shown the potential for major heat in short duration with some relief quickly to follow. Thursday offers our region its best chance of approaching this list provided we avoid 90 degrees on Friday.