Drought in Iowa, July 20 to 30, 1999

The most intense hot and dry weather to affect Iowa in the last four years occurred during the last half of July. A large sub-tropical ridge of high pressure developed over the central U.S. as the drought that was widespread over the southern and eastern U.S. expanded northwest. Temperatures warmed into the mid to upper 90s, and occasionally over 100 degrees, for a 10 day period. Overnight low temperatures were in the mid to upper 70s for the most part. It was fortunate for the crops in the state that the dew point temperatures during the heat were unusually high. Dew point temperatures held in the mid 70s to low 80s during much of the period of hot weather. Rainfall was very scattered with most of it falling to the north of the affected area. Though the entire state was affected by the hot and dry conditions, most of the damage occurred over the south third of the state. The unfortunate thing was that the heat occurred during the critical pollination period. Typically, temperatures in excess of 95 degrees hinder the pollination process. This was the case this year with many reports of partial ear fill being reported. Losses over the south third of the state were near 20%. Total losses due to the heat were in the area of $110,000,000 in lost production. Fortunately for Iowa, there were no deaths directly attributed to the hot and dry conditions, though there were several occurrences that the heat may have played a role.