Iowa Weekly Growing Season Report

Preliminary weather summary for the week ending June 20, 2021

Through the middle of the month, much of Iowa experienced the driest start to June on record as unseasonably warm temperatures and low relative humidity gripped the state. The statewide average temperature was 75.6 degrees, 4.8 degrees above normal. With drought conditions persisting across Iowa, a shifting storm track brought much-needed rainfall to most of Iowa’s reporting stations along with severe weather, though precipitation deficits of up to 1.25 inches were reported in northeastern Iowa; only portions of southern Iowa reported above-average rainfall.

Afternoon temperatures on Sunday (13th) reached into the low to mid 90s with variable winds under a sunny sky. Overnight lows remained unseasonably warm, ranging in the low 60s to low 70s. Isolated, light showers pushed into northwest Iowa early on Monday (14th) as temperatures moderated from the previous day, generally in the 80s with a few passing clouds and a light breeze. With a large-scale high pressure dome parked over the Midwest and low dew points, morning lows into Tuesday (15th) ranged from the 50s northwest to low 60s southeast. Dry air and sunshine allowed temperatures to rise into the upper 80s and low 90s with reports of spotty haze in northeastern Iowa. Widely scattered thundershowers developed in western Iowa before sunrise on Wednesday (16th) as winds shifted to the south through the day boosting afternoon highs into the low 90s west to mid 80s east. Additional storms, some strong to severe, fired in northwestern Iowa during the late evening hours producing hail and strong winds from Buena Vista County south to Audubon County. Rain totals reported on Thursday (17th) showed widespread rainfall across a swath of western Iowa with lighter totals east as showers and thunderstorms moved through central and southern Iowa; Anita (Cass County) reported 0.78 inch while Manning (Carroll County) observed 0.96 inch with general accumulations of a few tenths of an inch at a majority of stations experiencing rain. Afternoon conditions were sweltering across much of Iowa with several stations reporting triple-digit temperatures; the statewide average high was 95 degrees, 14 degrees above normal.

A low pressure system propagating across northern Iowa produced stronger thunderstorms just before midnight and through Friday (18th) morning. Additional showers formed during the day as the atmosphere over southern Iowa destabilized into the evening hours, partially due to afternoon temperatures reaching into the 80s under clear skies and higher humidity. Severe thunderstorms formed in this environment with several large hail and straight-line wind reports south of Interstate 80; 2.50-inch diameter hail was reported near Lake Red Rock (Marion County) while severe straight-line winds flattened corn around Milton (Van Buren County). Rain totals at 7:00 am on Saturday (19th) were heaviest near the Iowa-Missouri border with almost 30 stations measuring an inch or more; six stations in Davis County reported more than two inches with a gauge in Drakesville dumping out 3.54 inches. Another strong low pressure system pushed across Iowa overnight into Sunday (20th) producing widespread and much-needed rainfall across most of Iowa with only 15 stations receiving no rain. The statewide average rainfall was 0.40 inch with Little Sioux (Harrison County) observing 2.10 inches; nearly 20 stations reported over an inch of water.

Weekly precipitation totals ranged from no accumulation at a few Iowa stations to 3.56 inches in Mediapolis (Des Moines County). The statewide weekly average precipitation was 0.68 inch while the normal is 1.32 inches. Little Sioux (Harrison County) observed the week’s high temperature of 104 degrees on the 17th, 20 degrees above normal. Elkader (Clayton County) reported the week’s low temperature of 49 degrees on the 15th, nine degrees below normal.