While it was plenty warm on Tuesday, the high end index values failed to materialize as humidity levels came in a bit below forecast levels and thus kept heat index values lower as well. It was still the highest heat index of the year so far for the state. The featured chart looks into heat index metrics for Des Moines with the top panel showing daily climatology along the the 2026 observations. The bottom panel shows the daily frequency of having a 100+°F maximum heat index. Frequencies steadily increase during June before topping out mid July. You can see the first week of September has higher frequencies than the first week of June! Today will be another very warm day with chances of severe thunderstorms over eastern Iowa.