Weatherz School: What’s the WBGT?
I was recently at a baseball game, and it was hot. I was sweaty just sitting there, trying to hide from the sun under an umbrella. I checked the temperature and was shocked to find that it was only 78°. I would have guessed about ten degrees more than that.
The weather I was experiencing wasn’t well represented by the temperature, or even the heat index. But there is a weather parameter that reflects the full picture of that hot day at the diamond, and it’s called the Wet Bulb Globe Temperature.
The Wet Bulb Globe Temperature attempts to describe how “hot” it is and the potential for heat related stresses. The problem is, it’s a mouthful and it isn’t used by most people. A more common indicator of heat related stress is the Heat Index. Let’s break down the differences between the two.
The Heat Index is a “feels-like” temp calculated from the temperature and humidity. A temp of 95° and dew point of 70° yields a heat index of 102°. So, a miserably humid heat is well represented.
But here’s the kicker; the Heat Index assumes you are in the shade. Direct sunlight can add as much as fifteen degrees to the heat index. That’s where the Wet Bulb Globe Temperature comes into play.
This is also determined by temperature and humidity, but the temperatures are measured in direct sunshine. In addition, it factors in wind speed, cloud cover, and even sun angle. The Wet Bulb Globe Temperature is the highest with clear skies and calm winds. It goes down as cloud cover and wind increase.
The Twin Cities National Weather Service office has a page dedicated to the Wet Bulb Globe Temperature. You can check the forecast daily. As the map moves into yellows, oranges, and reds, heat related stress increases.
To stay safe in the heat, it’s best to move plans out of peak heating hours, in the middle of the day. Take frequent breaks in the shade or A/C, and stay hydrated. Paying attention to the Wet Bulb Globe Temp helps sports teams stay safe and spectators stay comfy.