for metro Philly you have July 15th 1995 & then there's everything else, one of those events you'll never forget
a couple clips NCDC storm events database
"An oppressive heat wave gripped most of Eastern Pennsylvania. It
climaxed on the 15th as almost every location reported record
breaking heat. The dew point temperatures, reached into the 80s
across southern Pennsylvania that day, an almost unheard of
phenomena. This, combing with sweltering temperatures produced an
apparent temperature of 129 degrees in Philadelphia."
"Record breaking high temperatures on the 15th included 104F in Lancaster,
103F in Philadelphia (The highest in 29 years.) and Williamsport,
101F in Selinsgrove, 100F in Avoca, 99F in Harrisburg and 98F in
Allentown."