Evaluation of the Effectiveness of National Weather Service Heat Forecasts in North Carolina

Extreme heat is the leading cause of weather-related mortality in the U.S. As many as 700 people die each year as a direct result of the heat. Extreme heat also affects human health through heat stress and can exacerbate underlying medical conditions that lead to increased morbidity. The North Carolina Division of Emergency Management is currently developing a heat response plan with the goal of “providing timely, adequate, and sustainable heat emergency response and operational planning guidance, in coordination with state and federal agencies, to protect lives during a heat emergency.” The plan is to be activated, or triggered, in phases when one or more National Weather Service (NWS) forecast offices issues a heat advisory, heat watch, or excessive heat warning. To evaluate the effectiveness of these triggering criteria, the relationships between the issuance of NWS heat products and the number of emergency department (ED) visits for heat-related illness were examined across each NWS forecast region in North Carolina for the period 2007 to 2012. Results reveal that, while 3 to 7 percent of all summer days during the six year period met heat advisory, watch, or warning criteria, these days only accounted for 10 to 29 percent of all ED visits for heat-related illness. In other words, the majority of heat-related ED visits occurred on days that fell below the thresholds for an advisory, watch, or warning. While adjusting the triggering criteria would likely decrease the number of “unwarned” ED visits, doing so would also increase the number of heat products issued, which may desensitize the public to the seriousness of the heat hazard. Therefore, it is recommended that heat response plans incorporate awareness and prevention strategies that address the health effects of heat at temperatures below current NWS thresholds.