Iowa Weekly Growing Season Report

_{Preliminary weather summary for the week Sept. 15-21, 2025}

A nearly stationary cut-off low pressure system spun over the Upper Midwest throughout the reporting period, bringing above-normal rainfall to much of Iowa’s western three-quarters. Unseasonal warmth also persisted, with positive departures in the 10- to 12-degree range in eastern and southern Iowa. The statewide average temperature was 71.6 degrees, 8.6 degrees above normal.

Sunday (14ᵗʰ) afternoon was the warmest of the reporting period, with daytime highs in the mid-80s to low 90s under sunny skies; the statewide average high was 90 degrees, 14 degrees above normal. Scattered thunderstorms developed over central Iowa into Monday (15ᵗʰ) morning and continued into northeastern Iowa during the day. Temperatures rebounded into the upper 80s, with some locations in the southeast reaching the 90s. Additional storms formed in eastern Iowa toward evening before dissipating around sunset. Eastern Iowa recorded the highest totals: 1.98 inches in Sigourney (Keokuk County) and 1.99 inches in Mount Auburn (Benton County). Outside of these amounts, a broad swath of 0.25-to-0.75-inch totals extended from east-central to northeast Iowa. Winds shifted southeasterly into Tuesday (16ᵗʰ), bringing mostly clear skies and morning lows in the mid to upper 60s. Pulse thunderstorms developed intermittently throughout the day as the cut-off low pressure system provided energy and instability. With little steering flow, some storms in central and northern Iowa produced locally heavy rainfall and hail. Totals ranged from 2.13 inches in Burt (Kossuth County) to 4.25 inches in Fort Dodge (Webster County). Much of west-central Iowa received at least 0.75 inch, with another pocket of heavier rainfall in northeastern Iowa. Showers and thunderstorms persisted in western and northern Iowa into Wednesday (17ᵗʰ) morning, then shifted into central and eastern Iowa after noon. Temperatures varied widely, from the low 70s northwest to the low 90s southeast. Some storms were severe warned for hail and strong winds. The complex weakened as daytime heating ended, dissipating by nighttime. Four stations reported nearly half of their monthly rainfall in a single day, with totals from 2.01 inches in Carlisle (Warren County) to 2.37 inches in Eagle Grove (Wright County).

Thursday (18ᵗʰ) began with widespread, locally dense fog produced by warm surface temperatures, ample low-level moisture, and light winds. With the existing unsettled pattern, showers and a few thunderstorms continued across much of the state, though many stations reported lighter totals. In Jefferson (Greene County), two gauges measured 1.54 to 2.10 inches, while in Marshalltown (Marshall County), two additional gauges collected 1.30 to 1.39 inches. Many other stations reported between 0.10 and 0.40 inch, and the statewide average was 0.21 inch. Overcast skies persisted into early Friday (19ᵗʰ) as the stubborn low center over the Dakotas streamed showers into Iowa, particularly in the afternoon and evening. Light to moderate rain continued across southern Iowa through the morning of Saturday (20ᵗʰ) and lasted much of the day. Afternoon temperatures were pleasant, in the upper 60s to low 70s, though sunshine was limited. Southeastern Iowa recorded the heaviest rainfall at 7:00 a.m. on Sunday (21ˢᵗ), with amounts ranging from 1.00 inch at Mount Ayr (Ringgold County) to 2.30 inches in Milton (Davis County).

Weekly precipitation totals ranged from 0.02 inch in Fairfield (Jefferson County) to 4.54 inches in Fort Dodge. The statewide weekly average precipitation was 0.90 inch; the normal is 0.83 inch. Donnellson (Lee County) and Washington (Washington County) reported the week’s high temperature of 97 degrees on the 14ᵗʰ, averaging 18 degrees above normal. Spencer Municipal Airport (Clay County) observed the week’s low temperature of 49 degrees on the 21ˢᵗ, one degree above normal.