A potentially significant severe weather event is expected to unfold across Iowa later today and tonight as another powerful storm system moves into the Midwest. The greatest threat window for Iowa appears to be during the evening and overnight hours, especially across western, central, and southern portions of the state.
Large hail, damaging winds, and tornadoes will all be possible with storms that develop to our west this afternoon before tracking east across Iowa tonight.
Morning Storms Could Influence Afternoon Development
Showers and thunderstorms moved across Iowa early Monday morning, producing pockets of gusty winds and heavy rain. While those storms weakened as they pushed east, they may still play a role in how the atmosphere recovers later today.
We will be watching how quickly warmer, more humid air can surge back north into Iowa this afternoon. If enough recovery takes place, the environment could become highly favorable for severe thunderstorms by late day.
Despite the morning activity, confidence continues to increase that storms will redevelop to our west and move into Iowa this evening.
Timing of Severe Weather Across Iowa
Current projections suggest thunderstorms will begin developing across eastern Nebraska late this afternoon before moving into western Iowa during the evening hours.
- Western/Southwest Iowa: After 6 PM
- I-35 Corridor (Des Moines metro included): After 8-9 PM
- Eastern Iowa: After 10 PM and continuing overnight
Storms are expected to continue moving east through the overnight hours before gradually weakening toward early Tuesday morning.
Tornado Threat
The atmosphere across portions of Iowa may become supportive of rotating thunderstorms capable of producing tornadoes this evening.
Wind shear in the lower atmosphere is expected to increase significantly tonight as a strengthening low-level jet develops across the region. That setup can help thunderstorms rotate and sustain themselves as they move east.
While there are still some limiting factors regarding how unstable the lower levels of the atmosphere become, conditions may still support isolated tornadoes — especially with any discrete or embedded rotating storms that develop during the evening hours.
The tornado threat may be greatest across western and central Iowa during the evening before transitioning into more embedded circulations overnight as storms organize into a line.
Damaging Wind Threat
Damaging straight-line winds are expected to become an increasing concern as storms evolve into a larger complex tonight.
Some storms could produce wind gusts exceeding 60 to 75 mph, especially as storms organize into a fast-moving line while tracking east across the state.
Given the strength of the winds just above the surface tonight, storms may be capable of transporting some of that momentum downward, leading to pockets of damaging winds.
Large Hail Possible
Large hail will also be a concern with the strongest storms, particularly during the early stages of storm development across western Iowa this evening.
Very steep lapse rates and strong atmospheric instability could support hailstones reaching quarter size or larger, with isolated reports of significantly larger hail possible in the most intense storms.
As storms merge into a larger line later tonight, the hail threat may gradually decrease while the wind threat increases.
Stay Weather Aware Tonight
Because much of Iowa’s severe weather threat arrives during the evening and overnight hours, it will be especially important to have multiple ways to receive warnings before going to bed tonight.
Make sure wireless emergency alerts are enabled on your phone, and have a reliable method to receive weather warnings if warnings are issued overnight.
You can also stay updated throughout the day and tonight with the ISCN Weather app and by following updates from IowaWeather.com and the Iowa Storm Chasing Network Facebook page.