textproduct: Des Moines

KEY MESSAGES

- Early morning rain tapers off across the area by around 10am, then becoming warm, dry, and breezy. Wind gusts of 35-40 mph possible through the afternoon.

- There is an Enhanced Risk (level 3 of 5) for severe storms this evening. Strongest storms are expected in western Iowa with a line that will move across Iowa in the evening and overnight into Monday morning. Tornadoes, damaging wind, and large hail are all possible with this line of storms.

- The final day of severe weather in this active stretch is Monday with another Enhanced Risk (level 3 of 5) for severe storms. Storms are expected to develop in southwest Iowa late in the afternoon and move across Iowa through the evening. Tornadoes, damaging wind, and large hail are all possible with this line of storms.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 232 AM CDT Sun May 17 2026

Storms early this morning have settled across southern Iowa with an area of strong wind gusts occurring north of the line with drying north of the precipitation shield. Gusts of 55-65 mph were reported, but have diminished early this morning. Meanwhile, an MCS moving across Nebraska and Kansas has reached far western Iowa. It has diminished in strength this morning and is expected to continue to weaken as it moves across the southern half of Iowa this morning. Precipitation is expected to taper off quickly from 7-10am. It then becomes very warm, dry and breezy through the rest of this afternoon. Soundings continue to indicate mixing through dry low levels with wind speed of 35-45 kts at times at the top of the mixed layer. While these higher gusts may not make it to the surface, gusts of 35-40 mph are possible through the afternoon. These winds are owed both to the mixing and dry air at the surface and the tightening pressure gradient across the state as the surface low lifts north through the plains and midwest.

The surface low sets up across Nebraska and South Dakota by late this afternoon with convection firing in the vicinity of the triple point and south along a trailing boundary. The environment across Iowa ahead of the incoming boundary is ripe for severe storms. This will be a nocturnal setup for Iowa as storm reach western portions of the area around 02z and push across the area overnight, exiting east close to 10z. Strongest storms are expected west with diminishing strength as the line propagates east overnight. The 00z HRRR sounding at Estherville tomorrow evening at 02z provides a snapshot of the conditions available for storm as they move into the area. The environment is deeply unstable with 2500-3500 J/kg of SBCAPE and mid level lapse rates of 8C/km. Stretching through the low levels is there with 100-150 J/kg of 0-3 km CAPE. Hodographs are also favorably curved with streamwise values of 0.029 (this is pretty high). 300- 500 m2/s2 of 0-3km SRH will favor sustained rotating updrafts with 400+ m2/s2 at the 0-1km layer and even 300 m2/s2 for 0-500m. This is more than sufficient for tornadogenesis and could support strong and/or long lived tornadoes. This does not guarantee that scenario will occur, simply that the environment would support it in western Iowa. DCAPE values are also 1000-1200 J/kg. All of this is supportive of strong convection as the cells in northwest Iowa begin to grow upscale into a line as it moves east. This would be capable of tornadoes, large hail, and damaging wind gusts. Storms are expected to diminish in strength towards 06z and fully exit the area around 10-12z based on current CAM trends.

With storms exiting the area early there should be plenty of time for recovery through the day on Monday. This is the final day of severe weather in this active period as the upper level trough finally lifts up out of the area. The upper level support will create a more dynamic setup and has the potential to be the most robust day of severe weather of the period. Reflecting this, there is an Enhanced Risk (level 3 of 5) across Iowa with a Moderate Risk (level 4 of 5) just to the southwest of Iowa. We will have to watch the track closely as convection from tonight may influence changes to the track on Monday afternoon and evening. As it currently stands, storms are expected to develop in far southwest Iowa late Monday afternoon, growing upscale into a line of storms that pushes across Iowa through Monday evening. All hazards are once again expected including tornadoes, large hail, and damaging wind gusts. The environment once again includes 2500-3000 J/kg of SBCAPE with 300+ m2/s2 of 0-3 km SRH and 200+ m2/s2 0-1 km SRH (150+ m2/s2 0-500m), mid level lapse rates of 8C/km and 1000+ J/kg DCAPE. In addition to the severe storms risk, the hydro risk continues after repeated days of convection across the state. The progressive nature of both Sunday and Monday convection should help to mitigate more widespread problems, but it will be worth monitoring for areas that may be vulnerable.

LONG TERM /TUESDAY THROUGH SATURDAY/

Issued at 330 PM CDT Sat May 16 2026

The encore system will lift through the area on Monday, bringing the potential for widespread storms and heavy rainfall. Severe weather looks likely with this system, as the parameter space boasts 60+ dewpoints, very unstable, surface based conditions, and a good amount of kinematic support along the cool front passing west to east through the area. All severe hazards will be possible, including hail, damaging winds and tornadoes. Strong moisture transport will also lift into the warm sector of the Monday system, bringing plenty of liquid into the area. Storms should be fairly progressive along the cold front, but localized ponding or flash flooding is certainly possible, especially in areas that receive rainfall tonight and Sunday night as well. Likewise, more water being added to local rivers could lead to in-bank rises through next week. We then see a brief break in the active pattern through the middle of the week, with milder temperatures overhead.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 640 AM CDT Sun May 17 2026

Lingering showers across KALO and KOTM this morning will taper off in the next 1-2 hours. Then dry and breezy today with southerly winds gusting 25-35+ kts across all sites. Mainly VFR cloud cover this morning should become more scattered into the afternoon. Note a few observations report 200-500ft ceilings this morning, however these are isolated in what is largely a VFR cloud deck and conditions are not expected to become widespread. A line of thunderstorms will move into western Iowa after 00z this evening, pushing across Iowa through the overnight and exiting east at the end of the TAF period.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 8 AM CDT this morning for IAZ081-092>095.