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Dew points have hit 90 degrees at several Iowa weather observation sites this week. 

It’s part of a record heat dome that’s been shattering records and producing eye-opening temperature and heat index values across the central United States in recent days. 

The heat index in Lawrence, Kan., hit 134 degrees Monday afternoon. It hit 130 degrees in Ottawa, Kan. 

Many meteorologists and weather observers have commented on multiple dew point values at and above 90 degrees in western Iowa this week. Some believe sensor calibration issues could be producing inaccurately high dew point readings. 

That may be true in some cases. But there are also two main atmospheric and land use factors that may be causing dew points to spike to near if not above 90 degrees. 

The first is what we call “corn sweat.” It occurs as corn plants in the massive sea of cornfields in the Upper Midwest transmit moisture from soils into the atmosphere above the plants. The 

 estimates an acre of corn can pump out 3 to 4 thousand gallons of water into the air in a day! 

 multiple times about how Pete Boulay with the Minnesota Department of Natural Resources State Climatology Office did an informal experiment above the dense corn plot that recorded dew points as much as 1 to 5 degrees higher over the cornfield than surrounding areas at the same time. 

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. 

So it’s almost certain that corn sweat is boosting dew point values from western Iowa into southern Minnesota by several degrees this week. 

Record hot Gulf of Mexico water temperatures

The second factor that’s likely contributing to the astoundingly high dew point readings in the Upper Midwest this summer is 

. Water temperatures in the Gulf have hit 90 degrees in some areas from Texas all the way to Florida. 

Warm water in the Gulf of Mexico has been feeding extraordinary heat and moisture into air masses in the southern and central U.S. this summer. Southerly wind flow has pumped those tropical dew point levels into the Upper Midwest in the past week. 

Dew points reached the 80s at multiple locations in Minnesota Tuesday. The 

highest dew point ever recorded in Minnesota is 88 degrees

It may take some time to see how much sensor calibration issues factored into the incredible 90-degree dew points recorded in Iowa this week. But corn sweat and a superheated Gulf of Mexico air mass are also very likely significant factors.

Weather and Climate News

Updraft® - Minnesota Weather News

Paul Huttner

Author

What’s causing the incredible dew point levels in Iowa this week? 

What's causing the incredible 90-degree dew points in Iowa this week?

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