WeatherWeather Science


Meet the sibling of the heat index

How this variable may be more meaningful in Colorado dry heat
Posted at 4:26 PM, Jul 10, 2020

Heat index is a tried and true measure of how it "feels outside" during the warm and humid summer days. But, that's the thing, Colorado summers are typically warm and DRY. Heat index is used to determine heat advisories or excessive heat warnings.

Neither of these alerts have ever been issued by the National Weather Service in Pueblo... seriously, I asked them! This is a factor of our climate as well as our low dewpoints yielding "low" heat index. Temperatures get to the 100's often in the eastern plains, and along the low elevations of the Arkansas river basin.

Determining Heat Danger

The heat index compares temperature with dewpoint. On a hot summer day in Colorado, dewpoints are often below 50 degrees, which would keep the heat index and temperature similar.

While Colorado may not experience many brutally humid days, you can't tell me that standing in the shade versus direct sun doesn't play a role in how it feels. Or, if there is a breeze versus calm conditions.

This is where the wetbulb globe temperature (WBGT) comes in. It certainly doesn't roll off the tongue, but it is a variable that factors in temperature, dewpoint, wind, and the angle and amount on sun.

WBGT is another tool that can be used to determine if heat related illness is a risk on any given day.

It may not be as easy to understand as the heat index chart above is. But, you can calculate the forecast WBGT here.


If you get a value over 80 it is a heat risk. Over 90 and you need to just stay inside. On a 100+ degree day in Pueblo with a 50 degree dewpoint and full sun with no wind, that will fall in the 80-85 category. For an hour of outdoor labor, 15 minutes of that should be a break in the shade or inside.

Unless you are a weather and science lover like me, the wetbulb globe temperature may not have practical applications on the daily. Checking the heat index works just fine if you are planning a hike or some gardening.

But, it is is vitally important for employers, coaches or anyone with responsible for overseeing outdoor strenuous activities. An accurate measure of heat risk should be on a daily checklist for practice for the local high school football team, or military training with equipment on, or the daily work on a construction site.

Know the signs of heat illness

Listen to your body and keep check of others and save a life.