textproduct: Des Moines

KEY MESSAGES

- Thunderstorms are expected over parts of central and southern Iowa, mainly south of Interstate 80 today into this evening. A few strong storms with large hail and damaging winds may occur. Locally heavy rainfall of 1-3 inches is possible over far southern Iowa.

- Addition storms possible Thursday night and again Friday night.

SHORT TERM /THROUGH TONIGHT/

Issued at 255 AM CDT Wed Aug 19 2026

The main surface boundary has settled well to the south of Iowa and is over southern Kansas and Missouri early this morning. An intense low level jet (LLJ) has led to vigorous storms from Topeka to Kansas City and southeastward. A few showers and an isolated thunderstorm have been ongoing over far southern Iowa. High pressure moving into Minnesota with drier air moving into northern Iowa while mid-level moisture continues over southern Iowa. This has led to a moisture discontinuity over the state with PWAT values dropping below 0.75" north while remaining over 1.50" far south. Water vapor imagery and RAP Potential Vorticity 1.5 pressure surface analysis show a robust PV anomaly/short wave cluster moving from southeast Montana and into western South Dakota. This anomaly is stronger than previously expected the past 24-48 hrs and will lead to a more active weather day for parts of Iowa.

Intense storms have developed in advance of upper level system over south central South Dakota. The MUCAPE axis ahead of these storms does lead into southern Iowa storm motions indicators such as the Corfidi vectors and 850-300 mb winds, suggest these storms may follow the instability axis and into the state later this morning. The various CAMs continue to be hit or miss today and much like their performance for much of August. Conceptual model would place thunderstorms across southern Iowa today, with the potential for a few strong storms with large hail and/or damaging wind gusts. Assuming this mornings cloud cover will erode enough for destabilization, surface based convection is certainly possible. Organized storms are possible but there is no shear in the lowest 10 kft with very light winds present then overtopped by increasing speed shear. Even without the surface instability, sufficient instability aloft and potential for free parcel lift is expected for storm potential as static stability is low. Locally heavy rainfall is possible as well and WPC has placed a slight risk for Excessive Rainfall. That said, any heavy rainfall will likely be over far southern Iowa and an area that hasn't had much rainfall the past 72- 96 hrs. The storm potential will persist over southern Iowa through the evening hours and until the upper PV anomaly passes by.

LONG TERM /THURSDAY THROUGH TUESDAY/

Issued at 231 PM CDT Tue Aug 18 2026

Upper troughing over the eastern half of the CONUS continues for the foreseeable future with a ridge over the southwest. By the weekend, the ridge builds over the western U.S. while the trough deepens over the eastern U.S. A closed low looks to develop over the Great Lakes eventually shifting eastward into early next week while another low drops out of Canada and towards the Great Lakes early next week as well. The end result is we remain in upper northwest flow never fully getting under the upper ridge keeping the forecast relatively active with several chances for precipitation through the weekend and beyond. The closest we get to the upper ridge is Saturday into early Sunday which looks to be one dry period. Another is before that, later Wednesday night through much of the daytime Thursday as a surface high pressure moves across, and then again towards mid to potentially later next week when a longer stretch of drier weather may finally take hold. Shortwave energy will precede a cold front which moves through the area on Friday bringing the return of precipitation chances from around Thursday evening through a good portion of the day Friday, though it won't be raining everywhere during this entire stretch. The best moisture return looks to be over Nebraska into western Iowa and southern Minnesota Thursday night and then maybe more into Iowa on Friday. We never fully get an open Gulf during this timeframe, and lower level moisture is also cut off from the Pacific stream despite mid-level moisture much healthier. All this to say, the best (stronger) storm chances are in far northwest Iowa which aligns with the SPC Day 3 Marginal (Level 1 of 5) risk which runs until 7 AM Friday. Temperatures remain pleasant this week in the the 70s to 80s with slightly warmer temperatures (still in the 80s) on Friday ahead of the cold front pending cloud cover and shower/storm timing from the night before.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1124 PM CDT Tue Aug 18 2026

VFR conditions are expected to prevail through this TAF period. Fog mentions were removed from TAF mentions tonight as clouds blanket much of Iowa. With calm winds through the night, any area with clearing may see patchy fog develop, but confidence of clearing over a terminal is too low for TAF mentions. Through 09z, scattered showers may move over KOTM though minimal impacts are expected. Otherwise, showers and storms return to Iowa tomorrow, mainly in the western and southwestern portions of the state. As of now, the only terminal with a mention is KOTM with a PROB30 in the afternoon. The northern extent of this activity could lead to mentions at KDSM, but confidence is too low otherwise. Light and variable winds are expected across much of the area. Depending on the northern extent of a surface boundary, winds at KDSM may become light and from the north/northeast, although guidance is split on how far north the boundary makes it.

DMX WATCHES/WARNINGS/ADVISORIES

None.