May 17, 2026 Zach Sharpe 0

Iowa Weather: Tornadoes, Large Hail, and Damaging Winds Possible Across Iowa Sunday Night

Strong to severe thunderstorms are expected to develop across parts of Nebraska and South Dakota Sunday afternoon before tracking east into Iowa overnight. While much of the day across Iowa may remain quiet, conditions are expected to become increasingly favorable for severe weather later this evening and overnight as storms move into the state from the west.

We continue to monitor the potential for damaging winds, large hail, and tornadoes — including the possibility of a few strong tornadoes across western Iowa if storms can remain discrete before evolving into a line.

Timing of the Severe Weather Threat

The greatest severe weather threat for Iowa is expected during the overnight hours Sunday night into early Monday morning.

Storms are forecast to begin developing across Nebraska and South Dakota during the late afternoon and early evening hours. As these storms strengthen and organize, they are expected to move into western Iowa before continuing east across the state overnight.

The strongest storms are expected across western Iowa during the evening hours, with storms gradually weakening as they move farther east later tonight. Current guidance suggests storms may exit eastern Iowa between 5 AM and 7 AM Monday morning.

While uncertainty remains regarding exact storm mode and intensity, the environment across western and central Iowa appears highly supportive of severe thunderstorms.

Damaging Winds Could Become Widespread

Weather map showing wind threat levels across Iowa and surrounding areas; red zone indicates high wind gust potential near Sioux City, Storm Lake, Fort Dodge and Omaha, with yellow/tan and brown regions signifying lower threat levels. Includes a legend and a banner reading 'WIND THREAT' from IowaWeather.com (ISCN).

As storms organize into clusters or a squall line overnight, the threat for damaging straight-line winds is expected to increase significantly.

Forecast soundings show a very unstable atmosphere with strong downdraft potential capable of producing wind gusts in excess of 70 mph in the strongest storms. Some storms could evolve into bowing segments capable of producing widespread damaging wind reports.

The highest wind threat currently appears to be across western Iowa during the late evening hours before shifting east overnight.

Large Hail Possible With Initial Supercells

Weather map showing hail threat areas across the Midwest with color bands (red, yellow, brown) and a banner labeled 'HAIL THREAT' from IOWAWEATHER.COM in the upper left.

Before storms transition into a line, discrete supercells may develop across parts of Nebraska and western Iowa Sunday evening.

These storms would be capable of producing very large hail thanks to steep mid-level lapse rates and extreme instability. Some hailstones could exceed 2 inches in diameter in the strongest rotating storms.

The best opportunity for very large hail will likely occur across western Iowa near the Nebraska border during the evening hours.

Tornado Threat Continues Across Western Iowa

Banner reads 'TORNADO THREAT' over a color-coded weather map of Iowa showing red high risk, orange and yellow elevated areas, and green safe zones with town names like Sioux City, Des Moines, Fort Dodge, Ames, and Waterloo.

The tornado threat remains one of the more concerning aspects of this setup, especially across western Iowa Sunday evening.

Forecast models continue to show strongly curved hodographs, increasing low-level shear, and favorable storm-relative helicity values capable of supporting rotating supercells and tornado development.

If storms can remain isolated and surface-based before growing into a line, a few tornadoes may occur — including the potential for a strong tornado or two across portions of western Iowa. As storms become more linear overnight, the tornado threat may transition to embedded tornadoes within the line.

The exact placement of the warm front, amount of cloud cover during the day, and how quickly storms become linear will all play a major role in determining the overall tornado risk.

Uncertainty Still Exists

Despite the concerning setup, there are still uncertainties regarding storm evolution.

Morning cloud cover and leftover convection may influence how unstable the atmosphere becomes later today. Additionally, the timing and strength of forcing across Nebraska and the Dakotas will determine whether storms remain discrete supercells longer or quickly transition into a line.

Even with those uncertainties, confidence remains high that at least some portion of Iowa will experience severe thunderstorms tonight.

Stay Weather Aware Tonight

Because this will largely be an overnight severe weather event for Iowa, it is especially important to have multiple ways to receive warnings while you are sleeping.

Be sure to check back throughout the day for additional forecast updates as confidence increases in storm timing and impacts. Also make sure you have the ISCN Weather App installed so you can receive the latest severe weather information, radar updates, watches, and warnings as storms develop tonight.