Presented by Bradley G. Illston 1, Steven Piltz 2, and Steve Amburn 2 1 Oklahoma Mesonet; 2 National Weather Service Forecast Office, Tulsa, OK Utilizing Existing Meteorological Networks to Estimate Wet Bulb Globe Temperature as an Operational Tool for Heat Related Activities

Estimation of the impact of temperature, humidity, wind speed, and solar radiation on humans Its “values” are similar to a heat index ▫ However, the wet bulb globe temperature additionally accounts for sunlight exposure and wind speed Used extensively in military and athletics warm-weather decision making to better protect soldiers and athletes from heat-related injuries Wet Bulb Globe Temperature

Valuable tool for any person making critical decisions on outdoor heat- related decisions involving humans. The Wet Bulb Globe Temperature is calculated by combining natural wet bulb temperature, black globe temperature, and air temperature. WBGT = (0.7 * Nat. Wet Bulb Temp.) + (0.2 * Black Globe Temp.) + (0.1 * Air Temp.) …..but how can we get black globe temperature? Wet Bulb Globe Temperature

A key component in the calculation of WBGT is black globe temperature. The black globe temperature is an estimation of the value of a temperature taken inside a black globe exposed directly to the sunlight. For direct measurement, this requires a special instrument (i.e. black globe thermometer), which most meteorological networks, including the Oklahoma Mesonet, do not have. Black Globe Temperature Estimation

Dimiceli et al. (2011) showed that the black globe temperature could be estimated from actual meteorological measurements of air temperature, solar radiation, humidity, and wind speeds. A fourth degree polynomial equation was derived from which a linear equation was approximated. In 2010 and 2011, black globe temperature sensors were installed at the NWS Tulsa WFO and Norman Oklahoma Mesonet station, respectively. Comparisons of actual black globe temperature measurements to the formula derived from Dimiceli et al. showed that the black globe temperature was estimated to within 0.66°C, which ultimately contributes less than 0.15°C in error to the WBGT. Black Globe Temperature Estimation

Depending upon the value of WBGT, risk factors can be assumed These risks are a general estimation and can be altered ▫ if you are not acclimated to the weather ▫ if you are wearing different clothing (e.g. if you a wearing a military pack, add 10 to WBGT before determining risk) Wet Bulb Globe Temperature Risks

Color-coded risk categories are easier for the public than individual values. Especially when compared to heat index values. Wet Bulb Globe Temperature Risks

Adapted from: 1) USGS Survey Manual, Management of Occupational Heat Stress, Chapter 45, Appendix A. 2) Manual of Naval Preventive Medicine, Chapter 3: Prevention of Heat and Cold Stress Injuries. 3) OSHA Technical Manual Section III: Chapter 4 Heat Stress. 4) National Weather Service Tulsa Forecast Office, Wet Bulb Globe Temperature.

Public understands heat index and its values. Heat index is limited. Does not take into account wind speeds (which can help cool the body via evaporation) and cloud cover (which helps lower the radiational warming on the body). Comparison to Heat Index WBGTHeat Index Measured in the sunYesNo Measured in the shadeNoYes Uses TemperatureYes Uses RHYes Uses WindYesNo Uses Cloud CoverYesNo Uses Sun AngleYesNo

High WBGT values, but the heat index remained low Low wind speeds and sunny skies Different implications of the heat conditions Heat related advisories may not have been stressed to the public Comparison to Heat Index Case Study

Conclusion WBGT shows impact of temperature, humidity, wind speed, and solar radiation. Black globe thermometer not needed. Don’t abandon heat index…add WBGT. Use risk categories rather than values for general public. NWS is investigating making WBGT an NDFD element.

Brad Illston Thank You