ST. LOUIS – Heat and humidity strike back this week. High temperatures will climb back into the mid-90s and dew points back in the 70s later this week.
St. Louis weather is no stranger to heat coupled with high humidity, usually feeling more oppressive than dry heat. Our geographic location is partly to blame.
Being on the fringe of the corn belt, crops nearby increase humidity in the atmosphere, known as “crop sweat” or evapotranspiration.
“It kind of stands for two things,” said Kevin Deitsch, the warning coordination meteorologist with the National Weather Service. “Evaporation, the sun heats up water and it evaporates or turns to water vapor. And transpiration, which is the movement of water within a plant.”
This process is maximized over corn fields.
To break it down: after a good rain, crop roots soak in water from the soil. The plant absorbs the water and they ultimately sweat just like us. The plants release moisture into the atmosphere, thus creating higher dew points.
“This time of the year when the corn is healthy, it’s starting to get taller, the corn sweats or evapotranspirates, so we get really moist conditions around this vegetation,” Deitsch said. “And that can bring up our dew points and this sticky feeling outside.”
A higher dew point means higher humidity, making our bodies difficult to cool.
“If the dew point is lower, that means there is less moisture in the atmosphere and that allows our sweat to dry,” Deitsch said. “What that means is the sweat evaporates and cools our body. When it’s really oppressive and really moist outside, our sweat doesn’t evaporate all that easily, so our bodies stay overheated.”