Provided by Justin Glisan, Ph.D., State Climatologist, Iowa Department of Agriculture and Land Stewardship
Several weather disturbances brought widespread rains to Iowa during the first week of June, the start of meteorological summer. While northwestern Iowa reported above-average totals, the remainder of the state was near to below average on moisture. Temperatures also fluctuated through the reporting period as various air masses filtered across Iowa. Most of the state observed seasonal conditions with warmer readings in eastern Iowa and below-average temperatures in the northwest; the statewide average temperature was 66.6 degrees, 0.9 degree above normal.
A line of showers and thunderstorms continued moving across eastern Iowa into the evening hours on Sunday (29th) as gusty southerly winds pushed daytime highs into the low to mid 80s. A strong low pressure center over northern Minnesota fired severe thunderstorms along a cold front just after midnight on Monday (30th) with several northwestern counties reporting severe straight-line winds and hail. There was a lull in thunderstorm activity for much of the morning and early afternoon until the line refired in western Iowa ahead of the dry line, a demarcation boundary for higher dewpoint temperatures. A second wave of strong thunderstorms fired along the cold front as it pushed into central Iowa with afternoon temperatures in the upper 80s and 90s fueling atmospheric instability. The line was narrow and fast-moving with locally heavy downpours and additional hail and high wind reports. Overnight lows hung in the upper 50s and 60s under cloud cover and southerly winds. Event rain totals at 7:00 am on Tuesday (31st) were highest in northwestern Iowa with over 20 stations reporting at least an inch; Lake Park (Dickinson County) observed 2.07 inches while Spencer (Clay County) measured 2.27 inches. Stations in southern Iowa saw totals between 0.30-0.50 inch with lesser amounts farther east. The system finally moved out of southeastern Iowa in the early afternoon hours, where rain totals were at or under a few tenths of an inch, though Keokuk Lock and Dam (Lee Country) reported 1.31 inches. High pressure took hold of the Midwest into Wednesday (1st) with clearing skies and light, northerly winds. Daytime temperatures remained in the upper 60s and low 70s as an isolated disturbance brought light rain to portions of southern Iowa.
The pattern cleared into Thursday (2nd) morning with chillier lows observed in western Iowa under starry skies and light winds. Temperatures stayed in the 40s with a statewide average low of 47 degrees, eight degrees below normal. Afternoon highs reached into the mid to upper 70s under northwesterly flow, low relative humidity and mostly sunny skies. Friday (3rd) was slightly cooler as a disturbance approached from the northwest, bringing in light to moderate rain over northern Iowa through the evening and overnight hours. Rain totals measured on Saturday (4th) morning were under Sibley’s (Osceola County) 0.50 inch and generally in the 0.10 – 0.20-inch range at stations reporting rainfall over much of Iowa’s northern two-thirds. Spotty showers persisted through the day, especially in eastern Iowa where highs remained in the low to mid 60s, while mid to upper 70s were experienced in the southwest. Overnight lows into Sunday (5th) held in the 50s as clouds cleared and isolated pockets of fog formed in the absence of wind at multiple stations in central and western Iowa.
Weekly precipitation totals ranged from 0.05 inch in Sac City (Sac County) to 3.19 inches at Spencer Municipal Airport (Clay County). The statewide weekly average precipitation was 0.64 inch while the normal is 1.17 inches. Oelwein (Fayette County) reported the week’s high temperature of 92 degrees on the 30th, 15 degrees above normal. Cherokee (Cherokee County) and Sioux Rapids (Buena Vista County) reported the week’s low temperature of 40 degrees on the 2nd, on average 15 degrees below normal.