textproduct: Des Moines

KEY MESSAGES

- A few showers and perhaps an isolated thunderstorm are possible (20%) late today (north) through Thursday.

- Frost and Freeze potential Thursday night and Friday night.

SHORT TERM /THROUGH THURSDAY/

Issued at 331 AM CDT Wed Apr 29 2026

Currently, a longwave trough continues to meander east over southern Canada towards the Great Lakes. On water vapor imagery, a shortwave trough is moving across Utah and a subtropical jet (STJ) is rounding the top of a ridge over Mexico. The STJ, combined with the flow around the base of the longwave and a departing cold front induced deep convection across the southern US this evening, which is now dissipating. There is some choppy cloud cover currently across the Midwest, and a few very light showers exiting eastward out of Iowa. PoP chances remain low across the state for the next 12 hours, as a sfc-800mb dry layer advects in behind the departing cold front.

The pattern over the next few days will feature the longwave trough sliding over the Great Lakes, leaving Iowa in a NW flow regime. Several days of shortwaves will round the western periphery of the longwave, making passes through the state. On Wednesday, a subtle cold front in Northern Iowa may be enough to create a few precip chances from afternoon extending into the evening. Cold air advection through the 850-600mb layer should steepen lapse rates just enough to yield some CAPE on the order of 100 J/kg. For this reason, any showers that form will have the potential for a few rumbles of thunder. Still, little QPF is expected with these as dry air in the low levels will be persistent all day Wednesday. The surface pressure gradient on Wednesday will be fairly weak, but winds may still be breezy and marginally gusty at times. The planetary boundary layer (PBL) will be fairly tall by midday and allow some stronger mid level winds to mix down, though winds in the mid levels aren't particularly strong either. Temps Wednesday will warm into the upper 50s to 60s by afternoon, and may fall into the mid 30s in northern Iowa into the night. A low chance for frost exists, as there will likely be enough cloud cover to stunt radiative cooling and prevent frost.

Thursday is overall quite similar, though a more respectable shortwave will approach the state into the afternoon. Through the morning, pacific moisture will advect in from the west, bringing Tds into the low 40s in southern Iowa. This, plus the potential vorticity advection and the subtle front continuing to sag southward will increase precip chances in southern Iowa through the morning and midday. Again, an unstable layer with several hundred J/kg of CAPE will form and allow the potential for some thunder with any showers. Winds will be similarly breezy given the tall PBL. Again, highs will reach the mid 50s to lower 60s.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/

Issued at 331 AM CDT Wed Apr 29 2026

Great lakes upper low pressure and subsequent troughing will lead to a generally cool northerly flow that will feature intermittent short wave passages. Precipitation chances from Thursday are expected to be mostly out of the are by Thursday evening. A broad area of Canadian high pressure will ridge into the state Thursday night and will settle south and be centered over Iowa late Friday into Friday night. The main forecast challenge is the overall frost and freeze potential. Good boundary layer decoupling appears likely Thursday night and with an earlier passage of the short wave, this will allow for more clearing and subsidence behind the system. A similar and perhaps even more favorable setup for radiational cooling arrives Friday night. Surface dew points will be even lower as the center of the high pressure arrives and may result in overnight lows dropping into the 20s over northern Iowa. Expect frost and freeze headlines for both night and if you have sensitive vegetation you would like to protect, make plans now. Modest warm advection and thermal ridging will occur Saturday and Saturday night as the high moves to the southeast and a short wave approaches from the north. Temperatures will gradually warm this weekend with some low precipitation chances on Sunday as the next short wave arrives. Highs are expected to be in the 60s and 70s Sunday through early next week.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 635 AM CDT Wed Apr 29 2026

Area of mostly VFR stratus is moving southeast out of the area. There remains a low chance of a brief period of MVFR conditions at KDSM early in the period. Cumulus clouds are expected to develop late morning and into the afternoon with bases mainly AOA 5 kft. The wind will become breezy and gusty at times today before diminishing again tonight. A few showers may occur over mainly northern Iowa tonight but probabilities remain low enough to exclude from this forecast.

DMX WATCHES/WARNINGS/ADVISORIES

None.