Wet bulb globe temperature: Why it could shut down the Air Force Marathon

Published: Friday, September 14, 2018 @ 2:39 PM

Meteorologist Kirstie Zontini will let you know if the weather could slow you down for the race.

Have you ever heard of the term Wet Bulb Globe Temperature? Likely not, but it’s serious business at Wright Patterson Air Force Base, and it could force marathon organizers to call the race quits if WBGT reaches a certain level Saturday.

>>Air Force Marathon Forecast from Storm Center 7 Team

Storm Center 7 Meteorologist Jesse Maag explains what it means.

Content Continues Below

“Often times on hot days, meteorologists will talk about the heat index, or the ‘feels like temperature.’ Air Force meteorologists have another method of measuring heat and they go to pretty great depths to calculate it,” Maag said.

The Air Force Marathon released a statement Friday about the heat concerns: "Safety of the runners and our volunteers is of paramount importance so we have protocols in place for a variety of contingencies including adverse weather conditions. We have color-coded advisories based on wet bulb globe temperature, which is the standard across the industry and accounts for temperature, humidity, wind and other factors. We have a fully-trained weather office that is constantly watching weather and advising leadership. At this time, weather forecasts indicate temperatures in the high 80s after 1 p.m., which could impact the heat index. This is typical for previous races. If the WBGT approaches the barrier for black conditions (>82 F) then we would begin reviewing procedures and potentially implement an orderly cancellation with runners taking shelter at first aid and water stations until busses arrive to bring them back to the finish line."

>>Traffic: What to expect marathon morning

Maag explained the heat index accounts for both the temperature and relative humidity, disregarding other atmospheric factors. 

The wet bulb globe temperature, or WBGT, used by the Air Force, takes into account not only the air temperature and relative humidity, but also the wind speed, sun angle, and cloud cover.

>>Air Force Marathon: Racers expected from across U.S.

By using more variables, the Air Force expects to have a more accurate representation of the way the air feels on a hot day. 

The scale is slightly more complicated for the WBGT than the heat index, however. It doesn’t measure how the air feels like the heat index. For example, a calculated WBGT over 82 degrees is considered extremely dangerous.

COURTESY: Air Force Marathon organizers

That is the temperature at which the Air Force Marathon organizers would stop the race, according to an alert sent to participants Friday. 

So what will the WBGT be Saturday for the 2018 Air Force Marathon?

Storm Center 7 Meteorologist Jesse Maag said at 6 a.m. Saturday, temperatures are expected to start in the upper 60s with mostly clear skies overhead. 

By 9 a.m., skies will remain mainly clear with temperatures near the mid-70s. 

Around the noon hour, we’ll begin creeping into the lower to mid 80s with mostly sunny skies overhead. 

Around the noon hour, the heat index should only be around the upper 80s, and that will most likely mean a WBGT below 82. So while it is going to be warm, it shouldn’t be warm enough to have a major impact on the race.