The cooling effect of a thunderstorm is well-known, but today the region felt a dramatic example with the arrival of that fast-moving and destructive storm.
At 2 p.m., the official temperature was 97, the highest reading in Philadelphia since June 10, 2008. That came after one of the warmest nights on record.
Between 2 and 3, however, as the storm approached, the temperature plummeted 26 degrees. In a thunderstorm, the column of rain is quite cool. The water comes from the colder regions of the atmosphere, and the outflow of air from the storm cell can have quite a chilling effect.
This one flashed across the state at 55 m.p.h., and hurricane-force gust of 75 m.p.h. was measured at Philadelphia International Airport.
The extent of the damage isn't fully determined yet, but it is known that at least 100,000 utility customers lost power and that tree damage was widespread.
Chester and Delaware Counties were especially hard-hit, and so were sections of Philadelphia. Several large trees were down near Citizens Bank Park, where the Phillies spanked Cleveland in a rain-delayed afternoon game.
Our garden writer, Virginia Smith, reports that the famous 60-foot yellowwood at Bartram's Garden was severely damaged when it was struck by lightning. Bartram's will be closed tomorrow.
Another casualty of the storm was a somewhat esoteric record. Overnight, the temperature at the airport never got below 81.That would have topped the previous record-high minimum for the month of June, which was 80.
Thanks to that thunderstorm, however, the official low for June 23, 2010, will go into the books as a prosaically.
By morning, it should be considerably more comfortable.