Iowa Weekly Growing Season Report

Preliminary weather summary for the week ending September 19, 2021

While widespread rain fell across much of the state, unseasonable dryness persisted through the reporting period with the driest conditions found in southeastern Iowa; precipitation deficits of over 0.80 inch were observed with wetter conditions over Iowa’s northern half. Iowa also experienced warmer than average conditions with positive departures near seven degrees in southern Iowa. The statewide average temperature was 68.8 degrees, 5.9 degrees above normal.

A slow moving cold front continued to push across Iowa through Sunday (12th) afternoon, bringing scattered light rain showers to portions of Iowa. Daytime highs varied from the mid 80s in front of the boundary to low 70s behind with clearing skies. A line of heavier thundershowers formed over northeastern Iowa as the sluggish front approached the Iowa-Wisconsin border, leaving behind heavier rainfall. Totals reported at 7:00 am on Monday (13th) showed general totals of between 0.10 inch to 0.25 inch over much of Iowa’s northwestern half with a pocket of measurements above 0.50 inch centered near Waterloo (Black Hawk County); Independence (Buchannan County) observed 0.92 inch. A secondary warm front set up from west to east through the day, locking in warm temperatures across Iowa’s southern two thirds; north of the front, highs hovered around the mid 70s while mid 80s were reported south of the front. A low pressure center entered eastern Iowa around sunset, firing off stronger thunderstorms a few hours later; a severe-warned cell dropped 1.50-inch hail in Auburn (Sac County). Heavier showers also formed in northeastern Iowa as several stations reported a few tenths of an inch with Elkader (Clayton County) and Lake Mills (Winnebago County) both observing 0.33 inch. Winds shifted to a northerly direction as the low moved out of Iowa late Tuesday (14th) morning. Cloud cover gradually cleared off with afternoon temperatures in the upper 60s north to low 70s south. Generally dry conditions were observed into Wednesday (15th) as high pressure reigned across the Upper Midwest. Morning temperatures were chilly over northern Iowa with low to mid 40s observed at several stations while low 50s blanketed the rest of Iowa. Daytime highs remained near seasonal, in the upper 70s and some low 80s, under mostly sunny skies and light southerly winds. 

Thursday (16th) was warm with highs pushing into the upper 80s and low 90s in the northwest with gusty winds out of the south and clear skies; low to mid 80s were observed farther southeast with the statewide average high at 86 degrees, ten degrees above normal. A strong line of thunderstorms moved into northwestern Iowa along a cold front after midnight producing several reports of severe straight-line winds. The line weakened and continued across Iowa through Friday (17th) morning before dissipating. A secondary line of thundershowers popped up over extreme southeastern Iowa later in the afternoon. More than half of Iowa’s stations reported measurable rainfall below 0.20 inch with higher amounts in the northwest and southeast; Rockwell City (Calhoun County) measured 0.88 inch while Mount Pleasant (Henry County) reported 0.80 inch. Overnight conditions into Saturday (18th) were cooler than average behind the cold front with lows ranging from the low to mid 40s north to upper 50s south. Daytime temperatures reached into the mid to upper 80s in southern Iowa with upper 70s northeast under clear skies. Starry skies and a near full moon were visible through early Sunday (19th) morning with temperatures in the 60s, up to 12 degrees above average.

Weekly rain totals ranged from no accumulation at stations in southeastern Iowa to 1.04 inches near Harpers Ferry (Allamakee County). The statewide weekly average precipitation was 0.16 inch while the normal is 0.77 inch. Little Sioux (Harrison County) observed the week’s high temperature of 92 degrees on the 16th, 15 degrees above normal. Mason City Municipal Airport (Cerro Gordo County) reported the week’s low temperature of 41 degrees on the 18th, seven degrees below normal.