'Corn sweat' may help boost dew points to 80 degrees Saturday

Get ready for yet another extreme weather phenomenon in Minnesota this weekend — corn sweat.

I wrote in 2010 and 2016 about how evapotranspiration from the sea of corn across southern Minnesota and Iowa can modify our air mass through higher dew points.

The National Agricultural Statistics Service (NASS) reports U.S. farmers planted 91.7 million acres of corn in 2019. That’s about 69-million football fields.

Corn plants efficiently suck moisture from soils and evaporate it into the air. That can raise dew points above cornfields by 1 to 5 degrees.

Here’s a clip from my 2016 post.

Measurements by Pete Boulay at the Minnesota DNR Climate Working Group have found dew point levels from 1 to 5 degrees higher inside a relatively small corn plot at the University of Minnesota's St. Paul Campus.

Pete's brief experiment in 2010 confirms what other sources say about extensive corn crops adding to dew low level dew points. Dew point spikes of 1 to 5+ degrees are quite likely in the Upper Midwest in summer depending on wind velocity and trajectory.

Hello all,

There's been discussion about certain AWOS sites in Minnesota and their proximity to row crops, especially St. James. The dew point temperatures at sites like St. James are consistently higher than other locations during the high dew point season of July and August. Could the close proximity of actively transpiring crops be the explanation?

I wasn't quite hot enough on Thursday, so I did a little dew point experiment on August 12 using a "pshychro-dyne" instrument. I measured the wet and dry bulb temperature at the St. Paul Campus Weather Station and the small, but dense corn plot in front of the station. It was a sunny day with very few clouds. Winds were light before noon, but became fairly breezy from the south by afternoon. Readings were measured at 5ft above the ground and were conducted in either shade or in the instrument shelter.

Observations...

The dew point temperature was higher in the corn by 1-5 degrees F, wind may play a role. It feels very hot and muggy in the middle of a corn field in August.

Pete Boulay - Minnesota DNR Climate Working Group

80-degree dew points Saturday?

A few forecast models crank out dew points above 80 degrees Saturday afternoon across southern Minnesota. Most of that is due to a tropical air mass from the Gulf of Mexico. But evapotranspiration from the sea of corn will likely add a few degrees dew point (and heat index) values Saturday.

NOAA’s NAM model cranks out potential heat index values over 110 degrees across southern Minnesota Saturday afternoon.

Could Saturday bring the highest heat index values of summer to some Minnesota locations? Stay tuned.