INDIANA, USA — Add the wet bulb globe temperature (WBGT) to you list of weather words to gauge how hot the weather is going to be. It is an advanced way to measure heat and the impact it will have on humans outside. This is becoming a leading forecast variable to summer weather outdoor events and sports.
For the latest heat forecast, tap HERE.
It is an advanced calculation of air temperature, solar angle and radiation, humidity, wind, and cloud cover. It can be hot and humid, but this number is a more accurate representation of how the sun actually feels on your skin and how easy it is to cool down.
Equation Estimation: WBGT = 0.7Tw + 0.2Tg +0.1Td
Looks complicated. It is adding up the humidity (Tw), the heat transfer between a human the surrounding environment (Tg), and actual air temperature (Td). These all together are also accounting for sun angle, cloud cover, and wind.
WBGT is more accurate for heat than the heat index because it also factors in wind and how much sun is beaming down on you. The range of numbers is broken down into 4 categories.
- Extreme: 90 WBGT degrees or higher — 45 minutes of breaks every hour
- High: 88-90 WBGT degrees — 40 minutes of breaks every hour
- Moderate: 95-88 WBGT degrees — 30 minutes of breaks every hour
- Low: 80-85 WBGT degrees — 15 minutes of breaks every hour
These thresholds have specific recommended actions for doing work or play outside. The National Weather Service in Tulsa, Oklahoma and Oral Roberts university have a study on how they estimate this type of temperature without a globe thermometer.
WBGT in sports
Many states and individual school districts have maximum wet bulb globe temperatures that kids can play in. Many school districts across the country start implementing mandatory breaks with water near 90 WBGT degrees. At 92 WBGT degrees and above, outside sports are suspended. It's too hot to play.
The wet bulb globe temperature varies throughout the day, just like normal air temperatures. As the sun gets higher in the sky, as humidity goes up from south winds or plants giving off water, this number goes up.
For example, in 2024 the day after Father's Day, central Indiana has a higher heat stress forecast. The wet bulb globe temperature will hit the moderate category. This highlights that the weather will be very hot and humid and will make outdoor work and play more exhausting. However it is not high enough for widespread cancellations.
Notice how the highest wet bulb globe temperatures are hit in the afternoon and early evening. Once the sun starts setting, the WBGT starts to fall again.
In the morning, the wet bulb globe temperature is usually not high enough to cancel events.
Heat stress maps
The NWS has released an experimental heat stress index map. It is similar to wet bulb globe temperature, but it also takes into account how long lasting the heat will be in a day, and how unusual this type of heat is for a particular time of year. You can access this map HERE.
At WTHR, we will show the wet bulb globe temperature map to see which parts of Indiana will be the hottest and most humid.
Get ready. This summer looks very hot across the United States. More so than normal...
— 13News Meteorologist Matt Standridge