textproduct: Des Moines

KEY MESSAGES

- Lingering showers and weak storms are expected to continue generally over the western half of Iowa this morning, drying out into the afternoon.

- A front moving through Tuesday will lead to continued chances for showers and storms. This looks to occur over two rounds; The first over north/north-central Iowa through the morning, and a second later in the afternoon to evening. Isolated strong to severe storms, as well as heavy rain are possible, with higher chances Tuesday evening/early Wednesday.

- Cooler temperatures and lower humidity arrive late week.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 305 AM CDT Mon Sep 7 2026

Lingering showers with some isolated areas of embedded weak storms are ongoing over portions of western Iowa this morning. This activity is elevated and is being fueled by deep moisture convergence within a ribbon of relative weak instability around 500 J/kg, as a 25-30 knot low level jet sits overhead. The expectation is that with little change in the environment over the next several hours, similar activity is expected to continue generally west of the I-35 corridor, before slowly decreasing in coverage by late morning and especially into the afternoon. Additional rainfall amounts this morning should generally read under an inch. Drying conditions will return as forcing aloft decreases, along with the push of drier air as surface high pressure currently centered over the Great Lakes dominates overhead, pushing the instability axis westward. While the mid-level ridge becomes more centered over the Midwest briefly today, a push of 850mb warm air advection is expected to occur, with efficient mixing and a tightening pressure gradient allowing for surface winds to become breezy by late morning and through the afternoon. Gusts up to 20-25 mph will be common, with locally higher gusts up to 30-35 mph over northern Iowa. Highs are expected to remain cooler compared to the recent hot conditions experienced, as thick cloud cover is slow to decrease into the afternoon, with forecast values reaching into the low to mid 80s.

As a potent trough moves into Manitoba, Canada late tonight, an associated boundary extending from Minnesota through the Dakotas is expected to gradually track into Iowa through Tuesday. Ahead of this boundary, showers and thunderstorms are forecast per guidance to arrive into north/northwest Iowa around if not just after midnight. A strengthening low level jet is expected to have more of an influence into Iowa as it expands across the state, along with a push of theta-e advection overhead. A closer look at the environment features relatively limited instability amounts across northern Iowa of less than 1000 J/kg, along with shear around 25-30 knots and lapse rates around 6.5-7 C/km, which would indicate a low severe risk into Iowa with this morning activity. Cannot rule out some sub- severe wind gusts, and periods of heavy rain though as PWATS are indicated around 1.5-1.75 with deep warm cloud depths. Lingering dry air overhead may delay the timing of showers and storms slightly as soundings indicate, so will be something to monitor and adjust as needed.

As the jet fades through the morning, the coverage of showers and storms looks to decrease as the front slowly descends southeast, with a continued low severe threat. Attention however turns to the late afternoon to evening timeframe Tuesday, as the cold front itself arrives into central Iowa, paired with stronger forcing for lift given a restrengthening LLJ and higher moisture levels pooling ahead of the boundary. Temperatures in the warm sector (central to southern Iowa) are expected to be quite warm in the upper 80s to low 90s, paired with dewpoints in the upper 60s to low 70s. Higher instability values around 2000-3000 J/kg, along with shear values around 30-40 knots are indicated per soundings overhead, which would be more favorable for potential severe weather. Isolated severe storms with damaging wind gusts and large hail are possible. There is an increasing potential as well per latest guidance for heavy rainfall Tuesday into early Wednesday, given the indication for training storms along the boundary and high PWAT values overhead around 2-2.5 inches. Rainfall amounts around 1-2 inches are expected at this time, though slightly higher amounts near 3 inches could occur in areas where repeated stronger storms pass through. Details will continue to become more clear in future forecast updates.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 322 PM CDT Sun Sep 6 2026

Storms will exit the region behind the cold front on Wednesday, ushering in cooler temperatures and lower humidity. Highs in the lower 80s are expected through Thursday, with precipitation chances potentially returning by Friday.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 627 AM CDT Mon Sep 7 2026

Showers with isolated storms are currently moving towards KFOD/KDSM. These will likely remain showers and only last a couple of hours, but there is a slight chance that they briefly produce some lightning. Rain is expected to last until 15z, but could linger longer and will be monitored. VFR conditions prevail from the midday into the evening, but the 6z-12z period will become more active. LLWS is likely across the state during that period, though it appears too marginal for inclusion in this TAF issuance. Thunderstorms also become more likely across the northern terminals but kept PROB30 for now.

DMX WATCHES/WARNINGS/ADVISORIES

None.