The new generation of heat/health warning systems: how they work

The National Weather Service is implementing a new generation of heat/health warning systems in major cities around the country. These systems, which are now operating in 16 Forecast Offices, are based on the health response of the population to heat in each city. Thus, the systems are customized for each urban locale and thresholds to call advisories or warnings vary from place to place. In addition, an air mass-based synoptic methodology is employed to develop thresholds beyond which human health deteriorates.

One unique feature of the system is that the same weather will not necessarily trigger an excessive heat warning throughout the summer. Less people are affected negatively by the heat late in the summer season, so a certain oppressive air mass may create an excessive heat warning call in June but not in August. In addition, the system relies heavily on consecutive days of oppressive weather. Thus, the first day of oppressive weather may not trigger a call, but the third or fourth consecutive day of the identical weather condition could.

The systems are housed on password-protected websites, which are visible to National Weather Service forecasters and health officials within the urban area. The systems have helped facilitate communication between forecasters and stakeholders within the community; thus, many cities now have more sophisticated intervention plans because of the introduction of these systems. Finally, it appears that the systems save lives, and a recent study on the Philadelphia system indicates that well over 100 lives were saved over a three summer period.