In the past, the National Weather Service (NWS) has largely relied on urban heat/health warning systems that are based upon somewhat arbitrary sets of maximum and minimum heat index values. Today, an increasing number of Weather Service Forecast Offices are utilizing new, more rigorous warning systems, designed to accurately identify those days most likely to cause health distress. There are several distinguishing characteristics within these heat/health warning systems: · Each system is customized to a particular urban area, and takes into account the unique meteorology, urban structure and demographics of that area. · These systems are based upon actual weather/health relationships, as determined by daily variations in human mortality. · Meteorological input goes well beyond atmospheric temperature and humidity, and an air mass-based synoptic methodology is employed to develop thresholds beyond which human health deteriorates.

Weather Service Forecast Offices will be utilizing these new systems as guidance in their issuance of excessive heat warnings and advisories. The systems are housed on password-protected websites, and provide the forecasters with a wealth of information regarding the nature and potential health impacts of the forecasted heat event. The systems will foster increased communication between the NWS and local governmental agencies that are responsible for instituting intervention activities whenever the forecasters issue an excessive heat warning. Additionally, a number of effectiveness checks will be utilized to determine if the system accurately predicts health outcomes, and if the systems are actually saving lives