textproduct: Des Moines

KEY MESSAGES

- Slight Risk (Level 2 of 5) introduced across northern Iowa Tuesday night into Wednesday morning. Damaging winds up to 75 mph the primary hazard.

- Heat Advisory extended through Thursday with heat indicies pushing upper 90s to triple digits across central and southern Iowa.

- Additional heat and storms continue through the end of the week into Labor Day weekend.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 300 PM CDT Tue Sep 1 2026

Tuesday will feature a mix bag of hot temperatures across southern Iowa and possible storms tonight which could be strong to severe across northern Iowa. What a way to kick off meteorological fall across central Iowa.

Today

Current surface analysis reveals a weak boundary lifting north, which may trigger a few showers and storms as it pushes through. Outside of tonights severe weather risk,the primary story remains the oppressive heat across central and southern Iowa. Highs will climb into the lower to mid 90s along and south of I-80. Heat indices will again reach the mid to upper 90s, with a few locations making a run at the triple digits. The ongoing Heat Advisories across southern Iowa remain in effect through Thursday.

Tuesday Night

Attention then turns to the severe weather threat across northern portions of the CWA tonight. Late morning analysis shows an H5 shortwave positioned over Wyoming, progged to track into the High Plains by this afternoon. Convection is expected to initiate this evening across southern SD and northern NE. As these storms progress eastward, they will tap into a favorable environment for upscale growth into a MCS, aided by a strengthening nocturnal LLJ. High Res guidance (HRRR, RRFS and NAM) consistently positions the nose of the LLJ across southern MN and northern IA. This moisture convergence zone will coincide with the highest instability and our highest confidence (40-60%) in severe weather. Forecast soundings depict MUCAPE values around 3000 J/kg and strong deep layer (0-6km) shear of 40-50 kts, easily supporting robust updrafts. As the MCS matures and consolidates a cold pool, dry entrainment in the lower levels will enhance downdraft potential, introducing a significant damaging wind threat with gusts up to 75 mph. While straight-line winds are the primary hazard, a QLCS tornado or two cannot be ruled out. Robust 0-3km shear (35-40kts) coupled with 50-100 J/kg of 0-3km CAPE will provide ample low level stretching potential for any line- embedded vortices. One limiting factor that may temper the overall severe ceiling is relatively weak mid level lapse rates, generally hovering around 6-6.5C/km. As storms move across the northern parts of Iowa, PWAT values will be around 2" which will support decent rainfall rates. Flash flooding could be concern late tonight in the heavier thunderstorms primary in the urban areas.

Wednesday

Following the departure of the morning MCS and any lingering precipitation, dangerous heat returns. Similar to today, upper ridging will build over the Plains and Midwest, bringing another round of hot temperatures and tropical dewpoints. The next window for convection arrives Wednesday night into Thursday as a warm front lifts into northern Iowa. Low-level moisture pooling ahead of the boundary will push dew points into the lower 70s, yielding 2000-2500 J/kg of MUCAPE. However, there is considerable uncertainty regarding storm convergence across the north,. Deep-layer shear looks weaker, and an intense capping inversion characterized by H8 temperatures of 23-25C, could suppress storm initiation.

LONG TERM /THURSDAY THROUGH TUESDAY/

Issued at 300 PM CDT Tue Sep 1 2026

As we head into the end of the work week and Labor Day weekend, additional showers and storms will be possible again Thursday night into Friday morning. Highs on Friday will once again climb into the lower 90s, coupled with oppressive dew points in the 70s. The ongoing Heat Advisory may eventually need to be extended through Friday. However, we opted to hold off on any extensions with this forecast package due to lingering uncertainty regarding the southward extent of Friday morning convection. Additional showers and thunderstorms chances will remain in the forecast through the weekend, alongside continued warm highs in the upper 80s and lower 90s.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 625 PM CDT Tue Sep 1 2026

Enhanced winds near 2KFT are expected late this evening into the overnight, resulting in wind shear at most sites on the order of 35- 45 knots. This should fade out across the state after 10z. Thunderstorms look to impact the far northern part of Iowa tonight, with exact timing somewhat uncertain. Confidence is highest for KMCW, but KFOD and KALO have ~20% chance of being impacted. Still, an outflow boundary with a wind shift and gusts may push further south to KFOD (60% chance). Variations in the LLJ will cause variations in the surface wind near sunrise, shifting more southeasterly near sunrise, and back to more southwesterly by mid- morning.

DMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory from 1 PM Wednesday to 7 PM CDT Thursday for IAZ057-058-070-071-081-092. Heat Advisory until 7 PM CDT Thursday for IAZ059>062-072>075- 082>086-093>097.