State Climatologist Justin Glisan says the drought-busting rains of July pushed the month to near the very top of the state record book
“We were beat out by of course the great flood year of 1993, but this July will go down as the second wettest on record,” he says. He says it will be a July many people will remember for the big storms. “Over nine inches of rainfall across the state and that’s nearly five inches above average. So particularly soggy conditions statewide in quite a remarkable month, in terms of rainfall,” Glisan says. He says we were about and inch-and-a-half from the all-time July record.
Glisan says the early dry months of the year kept 2025 from being another flood year like 1993. “We had capacity in the soil moisture profiles for infiltration, stream flows were lower than average as well,” he says. “So we had a repository both in the streams and the soil profiles to take up a lot of this moisture.” Glisan says there were two main sources of moisture that led to ample July rain. “Plenty of moisture detection from the Gulf. We also had some Pacific monsoonal moisture through the mid levels of the atmosphere that was also able to get into the upper Midwest. You have two of those moisture sources, plenty of fuel for thunderstorms to feed off of,” Glisan says.
Glisan says he gets asked a lot about the so-called “corn sweat” where moisture comes off the 13 million acres of corn in Iowa. He says it is another source of water that leads to rain. “It’s a few orders of magnitude below the large scale moisture infection from the Gulf and from the Pacific monsoonal moisture. But the evapotranspiration from the crop can add a few points to the dew point, and that’s where we can add a little more moisture into the atmosphere,” he says.
Glisan says the heat dome that set up around the third week of July that led to heat indexes in the triple digits, but not record heat. “Overall you look at the month in general, we were about two degrees above average, so not exceedingly warm outside of that heat dome,” Glisan says. Glisan says that heat did spawn storms, including the derecho that barreled across the state.
