textproduct: Des Moines

KEY MESSAGES

- Hot and humid today and tomorrow. Heat peaks on Monday, but could be tempered by storms and/or smoke aloft.

- Two rounds of storms are possible on Monday. Severe storms are expected and may produce damaging winds, along with hail and heavy rain. There is also a low tornado threat in northern Iowa.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 318 AM CDT Sun Jul 19 2026

The cool front that sank south across Iowa through the day on Saturday is draped across northern Missouri early this morning. In the wake, temperatures overnight have been much cooler than recent nights. Most areas are in the low 60s, though southern Iowa still sits in the low to mid 70s nearer the boundary. Patchy fog has developed in a few places early this morning and may expand through sunrise, though widespread dense fog is not anticipated. Despite the cooler morning temperatures, the thermal ridge will rebuild through the day with afternoon highs back into the upper 80s and low 90s. The rebuilding ridge will result in an instability axis setting up across western to southern Iowa this afternoon. There is little forcing in place today, however an isolated thunderstorm could develop there.

Our attention then turns to the pattern shift that is expected to result in two rounds of thunderstorms: overnight tonight into early Monday morning and again Monday evening. Strong theta e advection is anticipated into the area during the daytime which may result in the warmest day of this hot stretch. Forecast highs, for now, are in the mid to upper 90s. At the same time, convection chances in the morning could temper afternoon warming potential depending on how quickly things can recover. Smoke overhead is also possible and could also influence daytime temperatures. Given the uncertainty here, no heat advisory has been issued, but one may be needed if confidence in convective evolution and subsequent impacts to temperatures increases. If recovery occurs as currently forecast, heat indices in the afternoon could exceed 100-105 for much of the area.

Round 1: Overnight and early Monday morning. A shortwave trough will ride across Montana and the Dakotas Sunday, reaching the upper midwest overnight. Convection from this wave is expected to track across South Dakota overnight, decaying as it reaches Iowa with remnants moving across the state through the early morning. Most of this should be sub-severe by the time it reaches the state, however a few stronger cores may persist and could result in hail or a stronger gust.

Round 2: Monday evening. The atmosphere is expected to recover behind the early morning decaying convection with strong theta e advection into the area and an airmass that becomes deeply unstable by afternoon as the upper level shortwave tracks north of the state. Recovery in the warm sector of the associated surface low will result in 4000+ J/kg of MLCAPE across the area. The jet is robust as well, inducing 50-60 kts of 0-6 km shear. This shear will be more than sufficient for organized convection with well maintained and longer lived updrafts. As such, evening convection is expected to be much more vigorous than the decaying convection of the morning, and this is the primary window for severe storms. Storms are expected to develop along a cold front that will push across the state in the evening, though airmass thunderstorms ahead of the front are possible in afternoon especially on any lingering outflow boundaries from morning convection. By late afternoon convection is expected to initialize. It is possible that two areas of convection develop, as hinted at in recent CAM guidance. The first area would be near the surface low cutting across Minnesota into Wisconsin and northwest Iowa with the second along the trailing cold front with best convection west near the edge of the thermal ridge on the instability axis. As the cold front pushes across Iowa through the evening, convection is expected to become more widespread along the entire front trailing across Iowa. As it grows upscale into an MCS overnight expect that wind will be the primary hazard. Large hail is also a concern, especially with initial updrafts with steep mid and low level lapse rates of 7-8 C/km. Hodographs are fairly straight, but a tornado cannot be ruled out mainly near the surface low in northwest Iowa with enhanced stretching and a little better low level curvature. There is also plenty of moisture in place with PWATs around 2" with warm cloud depths exceeding 4000 m, which will allow for efficient rainfall. Progressive storm motions and dry antecedent conditions (along with mature crops) should mitigate most hydro concerns.

LONG TERM /TUESDAY THROUGH SATURDAY/

Issued at 243 PM CDT Sat Jul 18 2026

Showers and storms are expected to taper off after sunrise Tuesday, with surface winds shifting northwest as the mid-level trough and associated deepening low pressure system departs the region. A tightened pressure gradient on the backside of this system will bring breezy conditions through the day, with gusts up to 20-30 mph. Highs as a result will also be ''cooler'' with values in the 80s, and dewpoints in the upper 50s to low 60s. The pattern through midweek generally remains the same as the ridge remains west of the region and upper level northwest flow continues to bring slightly cooler and less humid conditions overhead, as highs generally top out in the 80s and dewpoints reach into the upper 50s to low 60s. Subtle waves riding the larger scale flow with periods of some level of moisture return though could bring additional chances of showers and possible storms to Iowa later Wednesday through Friday, though details are not as clear on exact timing and coverage details of this activity and will be refined in the coming days. More summer like conditions are expected to return near the end of the work week as temperatures gradually return into at least the low 90s as the ridge strengthens once again.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1248 PM CDT Sun Jul 19 2026

Haze due to smoke will continue to linger at/near the KALO and KOTM terminals in the near term, then gradually lift through this evening and especially Monday. Otherwise, generally VFR conditions are expected outside of some potential short-lived MVFR ceilings due to spotty cumulus development. Otherwise mid to upper level clouds increase most notably near the latter portion of the period, with a low potential for storms in northern Iowa and therefore the addition of PROB30 mentions in this issuance. Further details regarding exact timing and coverage will need to be refined in future updates. Light southeast winds will gradually shift SW late in the period and become breezy.

DMX WATCHES/WARNINGS/ADVISORIES

None.