textproduct: Des Moines

KEY MESSAGES

- 30% chance for showers and thunderstorms in far southern/southeast Iowa this evening. Strong storms, mainly with hail, are possible.

- Slight Risk (level 2 of 5) for severe weather now covering the western half of Iowa for Thursday. A Marginal Risk (level 1 of 5) covers the eastern half.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 259 AM CDT Tue Apr 21 2026

Midlevel clouds covered the state overnight and wind gusts continued in the southeast. This is in response to the LLJ overhead. A boundary could be seen in the wind field near Sioux Falls at 2am. This boundary will move across the state today, reducing the speed of the wind fields behind it. Theta-e advection continues ahead of it. The 850mb wind max will run parallel to the boundary by this evening. By this point, MUCAPE values over 1000 J/kg will collect on the boundary, which will be stalled near the IA-MO border. Last night, we mentioned that capping would focus the activity along the front east of the area, but trends tonight favor weaker capping, thus lower CIN. Strong storms can't be ruled out given the CAPE values mentioned as well as deep-layer shear values over 30kts (albeit in an orientation that will hinder storm ventilation). Since most of this activity will occur after dark, hail would be the main threat and be aided by the building EML (midlevel lapse rates will be around 8 C/km). We'll need to monitor to see if surface based storms can fire earlier (22z-00z) as strong winds will ensue. LCLs look to be too high for tornadoes at this time. If storms can take advantage of the SRH (~200 m2/s2) then any forming supercell would have a greater chance of severe weather.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 259 AM CDT Tue Apr 21 2026

A few trends of note for Thursday's storms. 1) Chances are increasing for pre-frontal convection Thursday morning as the instability axis increases from the southwest, most likely in the south and central part of the state. Severe hail will be the main threat with these. 2) The cold front continues to have a slowed arrival, reaching central Iowa closer to 00z. and 3) The favorable upper- level dynamics have continued to shift west as the shortwave trough ejects northeast sooner. Hodographs over Iowa have shown the trend best with a decrease in deep-layer shear, most of the shear now in the 0-3km layer. In response to the trends above, the Slight Risk has been moved more to the west, centered over Omaha instead of Des Moines. Damaging winds and large hail in isolated storms are the main concerns, although an isolated tornado can't be ruled out. A Marginal Risk covers areas east of Des Moines for the continued threat for hail and strong winds as deep-layer shear and daytime heating are both lost.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 645 AM CDT Tue Apr 21 2026

Main change this issuance was in winds for KDSM where it is now expected the terminal will maintain southerly winds after 00z instead of easterly. 20% chance in thunderstorms for KOTM between 22z and 01z, but have left out of TAF for now due to low confidence. Will continue to evaluate.

DMX WATCHES/WARNINGS/ADVISORIES

None.