Ag Weather Forum

For much of the Midwest, July 2025 will be noted as the wettest July in almost 10 years. A look at 30-day rainfall totals from June 30 to July 29 tabulated by the High Plains Regional Climate Center in Lincoln, Nebraska, shows that July rain totals were more than double the normal amounts in almost the entire western Midwest and in some big swaths of the eastern Midwest. That includes almost all of Iowa, where the rainfall total at central stations offers a good example of the heavy July totals. Ames posted 12.49 inches, 291% of normal; Des Moines, 10.62 inches, 287% of normal; and Marshalltown, 10.07 inches, 284% of normal (rain totals are from the Des Moines National Weather Service). The Des Moines total is a new record for the month of July.

Those Iowa rainfall totals are well into the top 10 historically. The state already had the sixth wettest July in 153 years of records as of Tuesday morning, July 29. Tuesday night rainfall may have nudged that standing up even more.

Atmospheric moisture to support the rain potential has been in ample supply all month, according to Iowa State Climatologist Justin Glisan.

"Thinking about the anomalous dew points and moisture in general, the Gulf moisture gate is open and moisture has been flowing north," Glisan said in an email. He also noted that saturated soil profiles in the southern states of the U.S. have been favorable for Midwest rain development. "Why this is important is that moisture is not extracted out of the air masses that are advecting north," Glisan said.

In addition to Gulf moisture, this year's summer monsoon flow in the southwestern U.S. has been active, which brings the Pacific Ocean into play as a source of moisture for the Midwest. Glisan noted that corn and soybean evapotranspiration has been a minor feature as well when it comes to adding to the atmospheric moisture supply.

"Studies have shown that during pollination and tasseling, corn can transpire anywhere from 3,000-5,000 gallons per acre per day," he said. "That may sound like a lot, but it's orders of magnitude smaller than the Gulf and Pacific moisture sources."

This midsummer rain coincides with corn pollination and raises the prospect of a significant boost in yield performance at harvest time.

"It has been a while since U.S. corn yields were above trend and even longer where a particularly good yield, such as 5% above trend, has been seen," noted DTN Contributing Analyst Joel Karlin on July 28. "A positive yield deviation that large applied to current USDA weather adjusted trend yield of 181 bushels per acre works out to 190 bushels per acre."

That is a lofty number, but the impressive Midwest July rainfall only adds to that potential.

Bryce Anderson can be reached at bryce.anderson@dtn.com

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