The summer of 2007 was noteworthy for its extended heat waves over large sections of the country. NOAA's National Weather Service (NWS), in conjunction with the University of Miami and Kent State University, is using one operationally-based guidance system (the Heat Health Warning System – HHWS) and one developmental product (the Heat Stress Index – HSI) to assist NWS forecasters to effectively communicate information regarding excessive heat to the American Public. The HSI demonstrated that a number of days registered stress values in the top 1 percent of a significant period during the summer, indicating that both intensity and duration of heat was significant for the season.

With these new tools, NWS forecasters can evaluate the duration and intensity of summer heat, as well as determine when heat produces a negative human health outcome in each city. The HSI uses five meteorological parameters to determine if a particular day is unusually stressful for any given place; the index varies from 1-10, with 10 being the most stressful possible day for a given locale for that time of year. Meanwhile, the new synoptic-based HHWS is designed to provide guidance to NWS Weather Forecasting Offices (WFOs) by estimating whether forecast meteorological conditions are stifling enough to produce excess deaths. The WFOs use this information to help determine whether heat advisories or excessive heat warnings should be called at a certain locale.