One of the weather risks that falls through the cracks of concern is heat stress. Maybe that’s because air conditioning is so prevalent in our homes, cars, and businesses. Maybe folks think Oklahoma’s a hot place and we should just tough it out. But heat can be a real risk, especially if you haven’t acclimated to the heat.
When you go outside are you ready for the heat? Do you know how warm it will be? Can you work or play without risk? Do you have an idea as you grow older of how much heat stress you can take? Do you know when young kids should reduce outdoor activities? Do you let an outdoor task dictate how long you will work or do change your work or play time to the heat conditions?
The Oklahoma Mesonet has a tool to help you monitor human heat stress conditions. It is a proven tool that can give you guidance to balance outdoor activities with rest periods. It is a tool that has been tested and refined by the U.S. Marines, Navy and Army since the 1950s. It has been used to protect and enhance athletic training. This tool is the Wet Bulb Globe Temperature map.
Mesonet Wet Bulb Globe Temperature maps are updated every five minutes. They use sunlight, wind speed and relative humidity to adjust air temperature.
How dangerous a risk category is to you depends on your level of heat acclimation, level of hydration, activity intensity, and how you balance activity and rest periods. Even with good hydration, if you are not acclimated to the heat you should not be outside working or playing when conditions climb into the High or Extreme Risk categories. Wait until conditions fall back into the Moderate or Low Risk categories. If you need to acclimate to the heat, get outside during Moderate or Low Risk conditions each day for two hours. While outdoors, mix activity and rest. You can divide the time into two one-hour blocks. Increase your activity time and intensity each day. It takes one to two weeks to fully acclimate to high heat conditions.
Plain water or sports drinks can help you get or stay hydrated. Drinks with caffeine, sugar or alcohol promote dehydration. Start hydrating one to two hours before you’ll be outside working or playing.
Wet bulb globe temperature is a different index than the traditional heat index that only uses relative humidity to adjust air temperature.
June 15, 2016 gave us a dangerously hot afternoon. Maps of the wet bulb globe temperature (previous WBGT map) and weather variables from 3:20 pm that afternoon give us a good case study to understand how the weather variables interacted to impact heat stress and wet bulb globe temperature values and risk categories. The air temperatures were hot across the state, ranging from 90 to 103 degrees F.
Recent rains gave us great soil moisture, but on this day all that soil moisture helped pump up relative humidities across Oklahoma. Even at 3:20 pm, for much of the state humidities were above 50%. Those higher humidities helped push the wet bulb globe temperatures into the Extreme Risk. Out in the Panhandle with relative humidities below 20% there was no heat risk.
The sunlight was generally bright across the state, with two areas of heavier clouds. One in the east and another in the southeast. The clouds in those areas lowered sunlight levels enough to drop the wet bulb globe temperature category to Moderate Risk. These were the yellow areas that included Westville and Cookson in the east and Idabel, Valliant, and Cloudy in the southeast.
Wind speeds were higher in the western half of the state. These higher wind speeds helped the western areas stay mostly in the Moderate Risk wet bulb globe temperature category. While eastern areas, fell into the High and Extreme Risk categories.
Along with the most current Mesonet Wet Bulb Globe Temperature map, you can view the Maximum Wet Bulb Globe Temperature maps for the current day and yesterday. All maps are in the Air Temperature group in the Mesonet.org Weather section.