textproduct: Des Moines

KEY MESSAGES

- The hot and humid conditions will continue throughout the week, especially over southern Iowa the next few days where heat index values will peak around 100 degrees. A Heat Advisory remains in effect for portions of southern Iowa through Wednesday afternoon.

- Thunderstorms will be possible at times for the next several days, but general coverage and frequency will be low. Only 20% chances are carried at times through Tuesday north of I-80. There is some potential for isolated severe weather Tuesday night/Wednesday morning over northern Iowa.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 242 PM CDT Mon Aug 31 2026

Surface conditions this afternoon are quite warm and humid across the forecast area, despite the push of upper-level cloud cover tracking northeast across Iowa per satellite imagery. Temperatures range in the low to mid 80s across the northwest half of the state, with warmer values south/east in the upper 80s to low 90s, while dewpoints sit in the upper 60s to 70s. These conditions are thanks to the prominent southwesterly flow in the low levels all the way up to 250mb, as the large ridge and associated heat dome remains parked over the southeast CONUS. Further west, a negatively tilted and rather strong shortwave trough is noted over southern Saskatchewan, while another trough, albeit weaker in comparison, is located over California/Nevada. At the surface, a southwest to northeast oriented boundary sits over far eastern Nebraska through northwest IOwa and southern Minnesota, tied to the aforementioned Canadian trough. Ahead of this boundary and closer to the weakened low level jet, some isolated weak storms had occurred at times through the morning, but were short lived as they lifted northeast across the state, only producing occasional lightning strikes and some brief rainfall. These earlier storms struggled due to the near surface warm layer that is winning out, paired with drier air and a lack of notable forcing to keep storm activity going. The remainder of the afternoon is expected to remain dry, with a very low chance for additional storms to develop given similar conditions working against storm development being more persistent. Continued warming will push temperatures a bit higher yet into the low to mid 90s, warmest southeast, where heat indices are expected to top out around 100-105 degrees. The Heat Advisory is in effect for the rest of today and will remain through Wednesday, as little change in the expected larger scale pattern will result in overnight lows in the 70s offering little relief and similar expected high temperatures and heat indices to today's values. Those who plan to spend time outdoors should stay hydrated and limit time directly in the sun to avoid heat illness.

Into the evening and overnight, the aforementioned boundary will have pushed further into Iowa, which guidance points its location somewhere over central to north central Iowa in more of a west to east orientation, as the quicker eastward moving upper level Canadian trough mentioned above tracks into Ontario. At the same time, increasing flow in relation to the low level jet maximizes over Kansas around 30-35 knots, and less so over Iowa around 20-25 knots. In terms of overall environment, shear values increase around 30-35 knots, along with MLCAPE values around 1000-2000 J/kg, while lapse rates sit around 6.5-7 C/km. The elevated warm layer overhead though, along with rather weak forcing for surface convergence and lift near the boundary would suggest rather limited potential for storms that may develop during this timeframe, which would be brief in nature and relatively weak. Therefore, have kept PoP coverage low into Tuesday morning, with this low coverage lifting north across the state.

Despite the low potential for showers and storms in the morning, the overall trend is for dry conditions to keep hold for much of the forecast area through Tuesday afternoon/early evening, with continued heat and humidity being the primary concern given higher certainty of occurrence and overall impacts. The next window of opportunity for showers and storms return through the evening into Wednesday morning, with a focus in development near the lingering surface boundary over Iowa. In terms of location of this boundary, model guidance continues to be varied on where exactly this feature will end up, as solutions vary from over north-central Iowa to southern Minnesota. Regardless of location, development of elevated showers and storms is suggested to occur late Tuesday night to Wednesday near and behind the boundary, with an environment more favorable for at least stronger storms given more favorable forcing as a stronger LLJ around 30-40 knots looks to develop, paired with instability values around 1000-1500 J/kg and mid-level lapse rates around 7.5 C/km. There is a low potential for isolated strong storms given this better environment for organized storms, with damaging winds the main concern given DCAPE values around 1000-1500 J/kg with the presence of low-level dry air per soundings, though hail is also possible if any stones can survive the steep warm layer below. Any showers and storms would gradually taper off through mid-late morning as the low-level jet fades, with capping overhead and a lack of forcing likely allowing for dry conditions through the rest of the day.

LONG TERM /THURSDAY THROUGH SUNDAY/

Issued at 242 PM CDT Mon Aug 31 2026

Into the end of the work week, the ridge over the southeastern CONUS flattens out somewhat, but still generally keeps its influence over Iowa, which will allow for the continuation of rather uncomfortable conditions with the heat and humidity. Forecast highs in mid 90s and heat indices around 100-105 degrees over much of southern Iowa are expected, which could lead to an extension in current heat headlines into Friday if forecast trends continue to lean that way, so stay tuned for updates. Additional shortwaves traveling through the western periphery of this ridge will continue to bring continued periods of showers and thunderstorms, particularly during the overnight and morning Thursday and Friday. Location of the associated boundary(s) and the influence of the cap overhead are still generally uncertain in this range, and even more so through the weekend considering how earlier activity in the week plays out, so will need to monitor trends over the coming days. For now, have left at least low PoP mentions over portions of the forecast area through the period given this overall potential.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1242 PM CDT Mon Aug 31 2026

VFR conditions are expected to continue across all terminals through the TAF period. Upper-level clouds will continue to pass overhead into Tuesday morning, with a remaining low potential (<20%) for some isolated showers and storms between 06-12z. Given low confidence in occurrence though, as well as exact location and timing of any storm coverage, have left out and will continue to monitor. LLWS is expected during this general time period at KDSM and KOTM, before fading following sunrise. There is a slight increase in fog potential based on latest guidance over KALO and KMCW, so have continued with 6SM BR mentions and may have to lower vsbys further if trends continue or if the increase the overall potential occurs.

DMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 7 PM CDT Wednesday for IAZ059>062-072>075- 082>086-093>097.