Monthly Weather Report

Iowa Monthly Weather Summary – May 2026

General Summary

Temperatures averaged 60.8 degrees or 0.9 degrees above normal while precipitation totaled 2.88 inches or 1.96 inches below normal. May 2026 ties 2004 and 2006 as the 60th warmest and ranks as the 35th driest May in 154 years of statewide records. A warmer May occurred in 2024 while a drier one occurred in 2025.

Temperatures

Temperatures across Iowa were near to slightly above normal through the month with the warmest conditions across central to northern Iowa. However, much of the state experienced near-normal temperatures. Sioux City Airport (Woodbury County) reported the month’s high temperature of 95 degrees on the 25th, 19 degrees above normal. Sioux City Air National Guard Base (Woodbury County) reported the month’s low temperature of 22 degrees on the 7th, 21 degrees below normal. May’s statewide average maximum temperature was 73.8 degrees, 2.7 degrees above normal while the average minimum temperature was 47.9 degrees, 0.9 degree below normal.

Heating Degree Days

Home heating requirements, as estimated by heating degree day totals, averaged 11% less than last May and 11% less than normal. Heating degree totals are 3% less than last year at this time and 11% less than normal.

Precipitation

May featured several rounds of rainfall-producing systems interspersed with extended dry and warm periods. Precipitation was generally episodic, with the heaviest rainfall tied to severe thunderstorm outbreaks during the middle and latter portions of the month. Rainfall distribution was highly variable, with localized swaths of excessive precipitation exceeding five inches while other areas received only light amounts from isolated showers.

Early in the month (May 4–14), precipitation was generally light and scattered. Rainfall was largely confined to southeastern and eastern Iowa on May 4, where Lee County stations received up to 0.96 inch. Additional weak disturbances on May 7, 12, and 14 produced mostly light totals under 0.30 inch, with measurable precipitation concentrated across eastern and northeastern Iowa. A significant shift occurred from May 15–18 as multiple severe weather episodes crossed the state. Widespread rainfall accompanied these storms, with more than half of Iowa's stations receiving at least 0.30 inch on May 15 and totals reaching 1.40 inches in Allison (Butler County). On May 16, heavy rainfall expanded across southern Iowa, where nearly 20 stations reported at least 2.00 inches and another 30 stations exceeded 1.00 inch.

The most widespread event occurred overnight May 17–18, when every reporting station measured precipitation. Amounts of 0.50 to 0.75 inch were common statewide, with localized totals of 2.00 inches in Le Mars (Plymouth County) and 3.00 inches in Bedford (Taylor County). A second round of storms later on May 18 generated a narrow corridor of excessive rainfall across southern Iowa, including 2.02 inches in Osceola (Clarke County), 3.18 inches in Pella (Marion County), and 5.30 inches in Mount Ayr (Ringgold County).

Following a brief dry period, another storm system brought widespread rainfall to northwestern Iowa on May 21–22. Stations across the northwest one-third of the state generally received at least 0.25 inch, while several locations exceeded an inch. The highest totals included 1.04 inches at Spencer Municipal Airport (Clay County) and 1.48 inches at Sioux City Airport. Late-month precipitation was more localized and convectively driven. Thunderstorms on May 24–25 produced rainfall of 1.10 inches in Rock Rapids (Lyon County) and 1.22 inches in Sheldon (O'Brien County).

Additional storms on May 25–26 dropped 0.97 to 1.63 inches near Osage (Mitchell County). The final widespread rainfall event of the month occurred from May 28–31 as a low-pressure system over the Plains transported moisture into Iowa. Southwestern Iowa received the heaviest totals, including 2.20 inches in Hastings (Mills County), while later thunderstorms expanded across western Iowa with 1.07 inches in Council Bluffs (Pottawattamie County) and 2.02 inches in Shenandoah (Page County).

Severe Weather

May was an active severe weather month across Iowa, with multiple outbreaks producing tornadoes, large hail, damaging winds, and localized flooding. The first severe storms occurred on May 4 when a cold front triggered thunderstorms across southeastern Iowa that produced small hail and wind gusts approaching 60 mph. Severe weather became more widespread on May 15 as a strong cold front swept across the state. Large hail was the primary hazard, particularly in northwestern Iowa where hailstones exceeding two inches in diameter were reported near Anthon (Woodbury County), Kanawha (Hancock County) and Meservey (Cerro Gordo County). Additional severe storms on May 16 were concentrated in southwestern Iowa, where hail up to 2.75 inches in diameter fell near Red Oak and a weak tornado was confirmed near Gravity (Taylor County).

The most significant outbreak occurred on May 17–18 as supercells developed along the South Dakota–Nebraska border and tracked eastward across Iowa. Preliminary reports indicated 20 tornadoes, all rated EF-1 or weaker, along with widespread damaging winds. Wind gusts reached 82 mph in Gruver (Emmet County) and 88 mph in Correctionville (Woodbury County) as storms evolved into a large bowing convective system. A second round of severe weather later on May 18 produced four additional weak tornadoes across southern Iowa and generated a narrow corridor of excessive rainfall. Another severe weather episode occurred on May 24–25 when thunderstorms across northwestern Iowa produced hail ranging from 1.00 to 1.25 inches in diameter.

Spring Summary

Temperatures for the three spring months of March, April and May averaged 52.0 degrees, 3.7 degrees above normal. This ranks as the 7th warmest spring on record. Precipitation totaled 10.29 inches or 0.21 inch below normal, ranking as the 45th wettest in 154 years of observations; Spring 2012 was warmer and the warmest on record while 2025 was wetter.

USDM

The US Drought Monitor (USDM) depiction released on June 4, indicated a trend towards degradation across much of Iowa. While the small areas of Severe Drought (D2) in northwest Iowa was removed, much of the state was classified D0 – Abnormally Dry conditions.  Additionally, the area of D1 – Moderate Drought have persisted in northwest Iowa and another area in the eastern part of the state has reemerged.  Currently, just over 70 percent of the state is experiencing some level of dryness, and nearly 3 percent is designated as some level of drought.

Justin Glisan, Ph.D.
State Climatologist of Iowa
Iowa Dept. of Agriculture & Land Stewardship
Hoover State Office Bldg.
Des Moines, IA 50319
Telephone: (515) 281-8981
E-mail: [email protected]

Weather by Districts

* Departures are computed from 1991-2020 normals. Due to the federal government shutdown, observations are still preliminary.
The weather data in this report are based upon information collected by the U. S. Dept. of Commerce, NOAA National Weather Service.