After the major heat wave of 1993, the City of Philadelphia embarked on a new way of identifying and mitigating the impacts of excessive heat. Research conducted by the University of Delaware showed success during a 1995 heat wave, and that work resulted in an operational program introduced in 1997 at the National Weather Service (NWS) Forecast Office in Mt. Holly, NJ for the City of Philadelphia. This new program supplemented traditional ways of determining the need for excessive heat warnings by expanding the criteria to include air mass identification, time of year, and length of excessive heat event.

Implementing the program required a concerted training effort for the meteorological operations staff of the NWS office, as well as local governmental partners and media. Education outreach on this topic is essential, as the impacts of excessive heat are still poorly understood by many people, even after the disastrous heat event in Europe during the summer of 2003. The partnership between the NWS office in Mt. Holly NJ and the City of Philadelphia can serve as a model for other urban areas as they develop and implement their own excessive heat programs.

A next generation program now uses gridded forecast data from the NWS National Digital Forecast Database as well as a more sophisticated statistical analysis of the excessive heat threat and promises an improved level of performance.