Written by Theresa Rose on July 30, 2018


By Dr. Justin Glisan, State Climatologist, Iowa Department of Agriculture and Land Stewardship

The last full week of July greeted Iowa with unseasonably cool temperatures and relatively dry conditions. Daytime highs over most of the state were in the lower 80s, two to three degrees below normal. Overnight lows were cooler as well, dipping into the upper 50s, four to six degrees below normal. Statewide precipitation totals were between 0.25 to 1.2 inches below normal; only parts of Mills and Fremont counties observed slightly above average precipitation. A cold front moved through Iowa early on Monday (23rd), bringing measurable rainfall to the state’s western third. Little Sioux (Harrison County) reported 0.52 inches of rain, while other locations in Sioux and Lyon counties observed between 0.25 and 0.33 inches. Tuesday (24th) was quiet statewide, with Bellevue (Jackson County) reporting the week’s high of 97 degrees. Active weather returned on Wednesday (25th), as another cold front moved through, firing up severe thunderstorms in north central Iowa. There were more than 10 reports of severe straight-line winds and pea to quarter-sized hail; Dows (Wright County) reported large broken tree limbs of up to eight inches. The line weakened and propagated through the eastern third of the state; Mason City (Cerro Gordo County) reported 0.80 inches of rain, while Waterloo (Black Hawk County) observed 0.16 inches. High pressure dominated Thursday (26th) and Friday (27th), bringing fair and cool conditions. Saturday (28th) was a wet day for western and southern Iowa, as a system brought measurable rainfall. Rathbun Dam (Appanoose County) recorded 0.98 inches of rain, the week’s highest accumulation; sixteen stations had accumulations of at least 0.50 inches. Thundershowers lingered into Sunday morning (29th), with isolated storms popping up in the afternoon. Weekend average highs were well below normal, especially in the southwest. Mount Ayr (Ringgold County) recorded a high of 66 degrees, 19 degrees below normal.