Preliminary Weather Summary

Written by Theresa Rose on June 2, 2020

Preliminary Weather Summary
Provided by Justin Glisan, Ph.D., State Climatologist, Iowa Department of Agriculture and Land Stewardship

The final week of May was warmer and wetter across much of Iowa as an active storm track brought multiple systems through the state; above average rain totals were reported at a majority of stations. Near seasonal temperatures were observed across western Iowa with warmer conditions farther east; the statewide average temperature was 66.3 degrees, 2.3 degrees above normal.

A line of strong thunderstorms with heavy rain continued moving through western Iowa into the early afternoon hours of Sunday (24th) before quickly dissipating as it moved into central Iowa. With southerly winds and clearing skies, daytime highs reached into the upper 70s and low 80s, allowing for instability to build in ahead of another disturbance that pushed into southwestern Iowa during the evening; this system produced a few strong thunderstorms along with a wide area of measurable rainfall. Totals reported on Monday (25th) were highest along a swath from southwestern to north-central Iowa with amounts generally at or above 0.50 inch; nearly 30 stations reported totals above an inch with Oakland (Pottawattamie County) reporting 2.42 inches. A southerly flow brought waves of showers and thunderstorms through the day with isolated severe thunderstorms across central Iowa. Johnston (Polk County) reported a brief EF-1 tornado with an estimated peak wind speed of 95 mph. Tuesday (26th) was another active day as a low pressure center spun into Iowa. Multiple bands of showers and thunderstorms moved through the state with several severe thunderstorms reported during the afternoon. Three weak tornadoes were observed in Dallas, Guthrie and Wright counties, though no significant damage was reported. Rain totals were highest in western Iowa with a majority of stations across Iowa reporting measurable rainfall; the statewide average was 0.33 inch of rain.

The low exited into Minnesota early on Wednesday (27th) as high temperatures topped out in the 70s under cloudy skies. Another line of showers and thunderstorms crept through the state ahead of a sluggish frontal boundary overnight and through Thursday (28th). Morning lows remained on the warm side, averaging 62 degrees statewide, nine degrees above normal. The front finally pushed out of eastern Iowa overnight as cloud cover thinned. Rain totals were highest in the northeast where Guttenberg Lock and Dam (Clayton County) reported 3.80 inches. General totals from 0.25 inch to 1.00 inch were reported from central to eastern Iowa with another pocket of heavy rainfall reported in southeastern Iowa; Brighton (Washington County) observed 2.25 inches. Friday (29th) was pleasant statewide with northwesterly winds and partly to mostly sunny skies. Daytime temperatures remained in the upper 60s and low 70s. Overnight lows into Saturday (30th) dipped into the low to mid 50s, with upper 40s observed in north-central Iowa. Another weak disturbance brought periods of showers across Iowa’s southwestern quarter through the day. Totals were generally light, though a small band of over one-half inch was reported across a few southwestern counties with Lamoni (Decatur County) reporting 0.60 inch. Amounts quickly tapered off northeast of this band. Morning lows on Sunday (31st) varied across the state with upper 40s in eastern Iowa under clear skies to upper 50s across western Iowa, where cloud cover was observed.

Weekly rain totals ranged from 0.12 inch in Remsen (Plymouth County) to 4.29 inches in Tripoli (Bremer County). The statewide weekly average precipitation was 1.57 inches while the normal is 1.07 inches. Muscatine (Muscatine County) reported the week’s high temperature of 89 degrees on the 25th, 12 degrees above normal. Elkader (Clayton County) and Stanley (Buchanan County) reported the week’s low temperature of 43 degrees on the 30th, on average eight degrees below normal.