Iowa Weekly Growing Season Report

Preliminary weather summary for the week ending September 21, 2020

Cooler and drier conditions persisted across the state through the reporting period as a quieter weather pattern settled over the Midwest. High-level smoke from western wildfire produced many hazy days as temperatures were up to three degrees below average in eastern Iowa; near normal conditions were reported across much of western Iowa with a statewide average temperature of 61.0 degrees, 1.2 degrees below normal. After the wettest week of the reporting season, no measurable rainfall was reported across Iowa, leading to deficits on the order of 0.60 inch to over 0.80 inch.

Sunny and seasonal conditions greeted Iowa Sunday (13th) afternoon as clouds finally cleared the state. Daytime temperatures were seasonal, in the mid to upper 70s with variable winds. Under clear skies, morning lows on Monday (14th) dipped into the low 50s with low-level patchy fog observed at locations around the state. Winds shifted to a southerly direction during the afternoon as temperatures pushed into the upper 70s and low 80s. Tuesday (15th) was a warmer day across Iowa as southerly winds picked up under clear skies. High temperatures peaked in the low to mid 80s, slightly warmer than normal. Overnight lows into Wednesday (16th) were in the upper 50s and low 60s with partly cloudy conditions reported in southern Iowa. A weak cold front propagated northwest to southeast through the day, shifting winds to a northerly direction and ushering in cooler air. Temperatures ranged from the low 70s north to low 80s south; southeastern Iowa reported some mid 80 degree readings. Skies stayed mostly clear allowing morning lows to drop into the mid 40s to low 50s. With a dome of high pressure dominating the upper Midwest, conditions remained unseasonably cool, sunny and dry across Iowa. Temperatures stayed in the 60s and low 70s with a statewide average high of 69 degrees, five degrees below normal.

Thursday (17th) was another cool day across Iowa with temperatures in the mid 60s north to low 70s south under sunny skies and a light northerly wind. Overnight temperatures into Friday (18th) were chilly across northern Iowa, where upper 30s were reported at some stations. Temperatures did vary across the state, however, with low 50s across southern Iowa and 40s moving north. The statewide average low was 44 degrees, six degrees colder than normal. A westerly wind built in through the day as cloud cover filtered across eastern Iowa. Afternoon highs remained in the mid 60s east to low 70s west, still cooler than expected for this time of year. A high pressure system to the east of Iowa produced southerly winds into Saturday (19th) morning with partly cloudy conditions throughout the state. Winds picked up into the afternoon hours as temperatures remained consistent with the previous day. A copper colored sunrise greeted the state on Sunday (20th) as high-level wildfire smoke persisted. Morning lows were generally in the mid 50s, though upper 40s were reported in eastern Iowa. 

While the normal precipitation for the week is 0.77 inch, no measurable precipitation fell across the state during the reporting period. Four southeastern Iowa stations reported the week’s high temperature of 86 degrees on the 16th, on average nine degrees above normal. Mason City Municipal Airport (Cerro Gordo County) reported the week’s low temperature of 35 degrees on the 18th, 12 degrees below normal.