A new product to evaluate the impact of heat on human activities, the Heat Stress Index (HSI), has been developed and is being evaluated by select National Weather Service (NWS) Weather Forecast Offices (WFOs) this year to determine if it has operational potential. The HSI is unique, as it is the only relative weather index currently in use. The index evaluates each day's weather and determines how stressful it is compared to the norm; the index varies from 0.0 to 10.0 and a day's value of 9.9, for example, indicates that only 1 percent of days at that place during that time of year would be more stressful in terms of heat.

The developmental test began on July 15 and ran through September 15 for ten WFOs . A password-protected website was established, posting the HSI twice daily, for access by each office. The values were used by each WFO as additional guidance on when to call heat watches, advisories or warnings, and were passed on to stakeholders, such as local health departments and emergency managers, to see if the product would be helpful for them as well.

Feedback from the WFOs on the index will determine next steps on how HSI can best be used to alert the American Public of heat hazards, including a recommendation as to whether it should be issued to the public. This paper will present the results of the feedback.