textproduct: Des Moines

KEY MESSAGES

- Frost/freeze headlines this morning for lows near and below freezing.

- Warming trend through Wednesday.

- Slight Risk for severe weather for southern portions of the area Thursday. Cooler weather to follow.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 340 AM CDT Mon Apr 20 2026

A dry air mass, clear skies and light winds were in place overnight. Radiational cooling will drop temperatures into the 20s north and east, justifying the Freeze Warning. The Frost Advisory covers where temperatures will drop close to freezing, but as noted in the previous discussion, the dry conditions will limit the formation of frost. The 850mb ridge will move to the east this morning and be replaced with southwest flow and WAA. Highs in the 70s will return in the southwest. The wind field in northwest Iowa will be elevated due to the distant influence of a low in southern Canada. Its boundary will move across the state Tuesday, the most noticeable change will be in wind direction. WAA continues and highs in the 80s will return Tuesday. Another ridge will move into Iowa late Tuesday and converge with the increasing moisture return to the south. The EML will be exerting its influence at this point, so its capping will likely lead to some low cloud cover in southern Iowa. Showers may manage to develop on the gradient of the cap in far southeast Iowa and into Illinois.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Issued at 340 AM CDT Mon Apr 20 2026

Speaking of capping, destabilization of the midlevels will continue, setting up the environment for severe weather Thursday. A shortwave trough will eject from its parent circulation, pivoting into the Dakotas early Thursday. Cyclogenesis will result, pulling the moisture axis ahead of a passing cold front. The low and midlevel jet will overrun the state of Iowa during peak heating Thursday, providing low and deep layer shear. Questions remain on moisture availability, which explains why CAPE values are lower at this range.

A large circulation centers itself over southern Canada, likely locking in cooler temperatures for Iowa this weekend. The evolution of the western CONUS trough is questionable into next weekend, but rain chances are nearby due to the amount of sources of synoptic lift at play.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1241 PM CDT Mon Apr 20 2026

VFR conditions are expected across the terminals through the period. Breezy south/southeast winds are expected through the evening, then turning more southwesterly through Tuesday morning, remaining breezy mainly over KDSM and KOTM. Widespread LLWS is expected overnight, ending after 12z. Winds shift further from northern to southern Iowa near the end of the period as a dry frontal passage enters the state, becoming northeasterly.

DMX WATCHES/WARNINGS/ADVISORIES

None.