‘Corn sweats’ added to weekend’s oppressive heat

You’ve likely heard in the past that it is not the heat, but the humidity - that makes all of us the most uncomfortable during the summer.

This past weekend, most of the Miami Valley baked under a “heat dome” that sent temperatures soaring into the 90s and rocketed the heat index over 100 degrees. The heat index is also known as the apparent temperature, and is what the temperature feels like to the human body when relative humidity is combined with the air temperature, according to the National Oceanic and Atmospheric Administration. While we have been in the 90s several times already this summer, the relative humidity - or more specifically - the dew point, had not been quite this high all year.

One of the reasons for the high humidity this past weekend may actually surprise you. In the summer, we normally have our hottest weather whenever a large high-pressure system anchors itself near or just off the east coast of the United States. The airflow around the high pressure is clock-wise. This airflow can bring northward very warm air from the south and moisture from the Gulf of Mexico. This flow can also bring moisture off of the Atlantic Ocean if it is strong enough.

But airflow is not the only reason for the sticky temperatures. Believe it or not this time of year, maturing corn in the fields can actually sweat and significantly increase in humidity. I’m sure you were likely taught about the hydrologic cycle in science class back in grade school. Well, moisture in the air not only comes from evaporation from lakes, rivers and oceans, but also occurs from plants in a process called evapotranspiration. Across the Midwest and here in the Ohio Valley this time of year we see lots and lots of corn - and yes - that corn can sweat, just like humans do. As air moves through the numerous fields of corn, that moisture is evaporated into the air.

According to the U.S. Geological Survey, during the growing season, just one acre of corn can sweat around 3,000 to 4,000 gallons of water per day. This moisture can add anywhere from 5 to 10 degrees to the dew point, which is a measure of moisture in the air. Dew point that is measured above 70 degrees is considered to be oppressive. Over the weekend, the dew point soared into the middle 70s to near 80 degrees from Iowa into Ohio. Yet, the dew point dropped off in areas that had less agricultural areas making it less humid.

The good news over the coming days is the high pressure system off the east coast will break down, at least briefly, to allow for slightly cooler temperatures and slightly lower humidity across the Miami Valley. However, the long-range outlook into August continues to indicate temperatures will be above average and yes, likely more days of high humidity. That means that you along with the fields of corn will likely sweat a lot more before the summer and growing season end. On the bright side - there are now only a little over 8 weeks until autumn arrives.

Eric Elwell is WHIO StormCenter 7 Chief Meteorologist. Contact him at eric.elwell@coxinc.com or follow him on Facebook and Twitter.