Lee wrote a summary for the NWS Des Moines website calling the emergence of a strong heat wave in late August unusual but not unprecedented.
“In 1976, a heat wave peaked on September 6-7 when temperatures reached as high as 103 degrees at LeMars. Amazingly, a strong cold front swept across Iowa a couple of days later, and on the morning of the 10th frost was reported in the lowlands with freezing temperatures at a few locations,” he wrote.
What is unusual isn't just the timing of the heat wave. Des Moines will almost certainly see four consecutive days with highs of 95 degrees or hotter for the first time since 1955. Ottumwa is expected to see three consecutive days above 95 beginning Monday.
Those are dangerous temperatures for those who spend a prolonged time outside, especially if the exposure includes strenuous activities.
People should be aware of how the heat affects them and stay out of the sun when possible. Drink lots of fluids and reschedule activities into the evening or early morning when possible.