National Weather Service United States Department of Commerce

A few minutes of exposure to direct sunlight can be extremely taxing on the human body, so it’s important to know whether or not it’s too dangerous to head outside – especially if you’re planning to engage in strenuous activities. Wet Bulb Globe Temperature (WBGT) – one of several NWS heat forecasting tools that you can use to prepare for extreme heat days in advance  – became operational on June 1. Operational products are supported by NWS employees 24 hours a day, 7 days a week.

Additionally, WBGT forecasts for the contiguous U.S. will be accessible hourly up to 36 hours, every three hours up to 72 hours, and every six hours up to 168 hours in advance. WBGT forecasts for Hawaii, Guam, and Puerto Rico will be available every three hours up to 72 hours in advance.

How is WBGT calculated?

WBGT takes into account temperature, relative humidity, wind speed, and solar radiation to estimate heat stress on the human body in direct sunlight. This newly operational forecast tool is most useful for active people who are spending time outdoors while engaged in physical activity.

Stay Weather-Ready

If you are an outdoor worker, athlete, or a part of another group that could benefit from WBGT forecasts, keep in mind that WBGT guidelines vary from region-to-region, so be sure to adhere to the advice of your local officials before engaging in outdoor activities.

To learn more about heat-risk and how to better protect yourself from the impacts of extreme heat, visit the NWS Heat Safety Tips and Resources page.