Last summer, Philadelphia, Pennsylvania, instituted a new Hot Weather–Health Watch/Warning System (PWWS) to alert the city's residents of potentially oppressive weather situations that could negatively affect health. In addition, the system was used by the Philadelphia Department of Public Health for guidance in the implementation of mitigation procedures during dangerous weather. The system is based on a synoptic climatological procedure that identifies “oppressive” air masses historically associated with increased human mortality. Airmass occurrence can be predicted up to 48 h in advance with use of model output statistics guidance forecast data. The development and statistical basis of the system are discussed, and an analysis of the procedure's ability to forecast weather situations associated with elevated mortality counts is presented. The PWWS, through greater public awareness of excessive heat conditions, may have played an important role in reducing Philadelphia's total heat-related deaths during the summer of 1995.
*Center for Climatic Research, Department of Geography, University of Delaware, Newark, Delaware.
+Oklahoma Climatological Survey, University of Oklahoma, Norman, Oklahoma.
#Philadelphia Department of Public Health, Philadelphia, Pennsylvania.
