Iowa Weekly Growing Season Report

Preliminary weather summary for the week ending July 12, 2020

Warmth persisted across the state during the reporting period with positive departures of up to five degrees. The statewide average temperature was 77.8 degrees, 3.3 degrees above normal. Several days during the period were also active with multiple waves of showers and thunderstorms, especially in northeastern Iowa. Below average totals of over an inch were reported in the driest portion of the state, namely west-central Iowa, while parts of eastern Iowa reported above-average totals.

Hazy conditions persisted through the late morning hours on Sunday (5th) as southerly winds and partly sunny skies pushed afternoon temperatures into the upper 80s. Overnight lows into Monday (6th) morning remained warmer than average, generally in the upper 60s and low 70s, as a complex of thunderstorms pushed into northwest Iowa. The system did not hold together for a long duration and dissipated over north-central Iowa during the early afternoon. Hot conditions again prevailed with highs in the upper 80s and low 90s with another line of storms pushing into western Iowa in the evening hours. Morning totals at 7:00 am on Tuesday (7th) from stations in the northwest corner of Iowa show amounts ranging from 0.10 inch at Remsen (Plymouth County) to 1.26 inches at a gauge in Sioux City (Woodbury County); rainfall was generally a few tenths of an inch at most stations. Scattered thunderstorms, some severe, formed across eastern Iowa during the afternoon hours with multiple reports of high wind gusts and tree damage. Radial damage to crops and trees in Quasqueton (Buchanan County) was likely a result of strong straight-line microburst winds; a 90-mph wind gust was also observed near Mount Joy (Scott County). The storms lingered into the late night hours and cleared eastern Iowa early Wednesday (8th) morning. Measurable rain was reported east of a line from the Quad Cities to Waterloo (Black Hawk County); Davenport Municipal Airport (Scott County) reported 1.24 inches with Dubuque (Dubuque County) observing 0.63 inch. Statewide morning lows, in the upper 60s and low 70s were up to 10 degrees warmer than normal; Fort Madison (Lee County) reported 75 degrees while the statewide average was 70 degrees, seven degrees above normal. With the warm start and sunny skies, highs were able to rise into the upper 90s across portions of south-central Iowa, making it the warmest day of the year so far. High dewpoints pushed heat indices into the triple digits; the statewide average high was 92 degrees, seven degrees above normal.

Balmy conditions on Thursday (9th) helped fire a line of severe thunderstorms through the evening hours, leading to a widespread severe wind event across northeastern Iowa. Heavy rain from the stronger storms was also reported in northern and eastern Iowa. Over 70 stations reported at least one inch with the statewide average rainfall at 0.51 inch. Swisher (Johnson County) observed 2.90 inches and was one of over 20 stations to report over two inches of rainfall. Friday (10th) was generally dry across a majority of Iowa with highs ranging from the low 80s north to low 90s south. A complex of thunderstorms pushed into western Iowa overnight into Saturday (11th) along an existing outflow boundary; additional storms fired in extreme northeast Iowa. Unstable conditions lead to an active weather day across Iowa’s eastern half. Strong thunderstorms moved through the eastern one-third of the state through the afternoon as another line of severe thunderstorms marched from north-central Iowa into the southeastern corner. There were widespread reports of severe straight-line winds and large hail on the order of 1.25 to 2.00 inches again causing additional crop damage. Rainfall reported at 7:00 am on Sunday (12th) showed totals in the range of 0.25 inch to 0.75 inch in Iowa’s northeastern one-third; St. Ansgar (Mitchell County) observed 1.88 inches.

Weekly precipitation totals ranged from no accumulation at multiple stations in southern Iowa to 3.68 inches in Anamosa (Jones County). The statewide weekly average precipitation was 0.92 inch while the normal is 1.05 inches. Osceola (Clarke County) and Perry (Dallas County) reported the week’s high temperature of 97 degrees on the 8th, on average 11 degrees above normal. Cedar Rapids No. 1 (Linn County) reported the week’s low temperature of 54 degrees on the 12th, 11 degree below normal.