The Development and Potential Benefits of an Apparent Temperature Climatology

Excessive heat was the biggest contributor to weather-related deaths in the United States during the period between 2007 and 2016. The primary tool that NWS forecasters use to assess excessive heat is the NWS Heat Index (NWSHI). The NWSHI was developed in 1990 by Rothfusz to fit a multiple regression analysis of the Apparent Temperature (AT) model developed by Robert Steadman in 1979. Subsequent work by Steadman expanded his AT model to include the variables of solar radiation and wind. Previous work by Wood and Keehn has shown that the inclusion of a variable wind has a significant effect on the AT in warm humid climates, and that the AT with solar radiation can be significantly higher than the AT in the shade on sunny days.

An examination of Houston area Heat Related Illness (HRI) data indicates that early season heat events (May/June) often result in multiple HRI hospital visits when the NWSHI is below the NWS regional threshold for an excessive heat advisory. These observations motivated us to develop a 30 year climatology of AT in the sun and shade at Houston area NWS Automated Surface Observing Systems (ASOS) sites. Similar to the NWS experimental HeatRisk Project, which associates heat risk based on the deviation from the daily temperature climatology, this work aids heat risk assessment based on an AT which includes all of the variables an individual experiences outdoors. In this study, we will present the methods and process utilized to develop an AT climatology, and also explore the benefits that an hourly AT climatology can provide to decision makers and the public. This climatology could also be used as the basis for the NWS to make a transition from a fixed AT threshold based heat watch/warning advisory to a variable AT threshold that better identifies early warm season heat risk.