textproduct: Des Moines

KEY MESSAGES

- Enhanced Risk (level 3 of 5) of severe storms this evening. Tornadoes, damaging winds, and large hail are possible as a line of storms moves west to east across the state.

- Cooler and dry through the middle of the week.

SHORT TERM /THROUGH TONIGHT/

Issued at 218 AM CDT Mon May 18 2026

Showers and thunderstorms continue to push east across Iowa early this morning. While the line of storms was initially robust in western Iowa last evening, producing damaging wind gusts and tornadoes, early this morning the cold pool has surged out ahead of the storms and weakened the storms significantly. Drying on the backside of the decaying MCS has resulted for wake low type winds to develop, with recent gusts of 40-50+ mph occurring. We will be watching this closely through the morning as a similar set up yesterday resulted in even stronger gusts. So far those have yet to materialize and this line is more progressive than yesterday's storms in southern Iowa. No hydro problems have been identified with the storms overnight tonight with the progressive nature of the line helping to reduce residence time over any single location. These storms are tied to a surface low currently centered over north central Iowa and south central Minnesota that will continue to move east this morning and through today. Meanwhile the primary surface low is centered across the panhandle of Oklahoma and southwest Kansas early this morning. This will eject northeast today as the upper level trough finally kicks east. This will serve as the impetus for convective initiation once again this afternoon, and will be the final round in this four day stretch of severe weather across Iowa. Evolution and expectations for severe storms will be outlined below, however it is important to note first that the ongoing/diminishing MCS across Iowa this morning will impact the evolution of storms later today. Storm strength this afternoon into Iowa will depend on how quickly the atmosphere can recover and how far north theta e advection can surge back north into the state after the cold pool shoves that boundary south.

CAMs indicate that the atmosphere should recover by late this afternoon with soundings largely uncapped across most of central and southern Iowa. This uncapped environment has 3000-3500+ J/kg of SBCAPE along with well curved hodographs through the low to mid levels. SRH values of 300-400 m2/s2 in the 0-3 km layer, 250-300 m2/s2 in the 0-1 km layer, and 200+ m2/s2 in the 0-500 m layer will be more than sufficient to maintain rotating updrafts through the mid levels and helicity for potential tornadogenesis in the low levels. The streamwise factor is also around 0.03-0.04 for storms to ingest efficiently. While shear/rotational factors are certainly in place for tornado genesis, low level instability is somewhat lacking. SBCAPE is quite high, but much of that is through the mid levels with steep 8C/km lapse rates. Low level 0-3 km CAPE is much lower at under 50 J/kg. Less low level stretching could help to limit tornadogenesis, but certainly cannot be counted on in an otherwise volatile environment. Storms are expected to initiate in eastern Nebraska around 21z and move into southwest Iowa around 22- 00z. The line will continue to push east across the state. The low level jet will strengthen after 00z, helping to maintain storms into central Iowa through 06z. Storms are expected to diminish in strength as they move east around and after 06z tonight. There is deep moisture transport into the area ahead of the upper level trough with PWATs of 1.5-1.75" across the area which should support efficient rainfall across the area this evening. The good news here is that the line of storms remains progressive and should limit most hydro concerns. Even so, pockets of 2-3" may be possible in southern Iowa where storms are more initially discrete/clusters before growing upscale and lining out across central Iowa. Given multiple rounds of precipitation over the last several days, capacity has diminished some, though most areas should still be able to handle the expected QPF. Primary areas of concern would be any heavy rain pockets that set up over towns. Widespread flash flooding is not anticipated to be a concern.

LONG TERM /TUESDAY THROUGH SUNDAY/

Issued at 342 PM CDT Sun May 17 2026

A much needed break from the active weather stretch begins on Tuesday as a high pressure nudges into the region later Tuesday into Wednesday. Mid-level winds behind the departing system Monday night also turn out of the north to northwest ushering in cooler temperatures with highs in the 50s to 60s on Tuesday through Thursday and lows Wednesday and Thursday mornings in the upper 30s to 40s. Winds on Tuesday will remain elevated through much of the daytime with a tight pressure gradient still in place with sustained winds out of the northwest 15-25 mph, and gusts to near 30 mph in the northwest. Showers and thunderstorms then return to the forecast from later Thursday into Friday as an upper trough crosses the Central Plains with a developing surface low reaching towards the area into Friday. Additional details to come in the next several days.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 636 AM CDT Mon May 18 2026

A few showers will affect OTM in the next couple hours, after which the bulk of the day will be dry. SSE winds will increase, mainly at ALO/DSM/OTM, while low clouds affect northwestern IA including FOD/MCW at times, where ceilings will be MVFR to possibly IFR at times. This evening into tonight, TSRA will move through the area followed by SHRA. Have included TEMPO groups for TSRA at all sites during the most likely time window, but expect that to be refined throughout the day. Low ceilings will also gradually spread across the rest of the area during that time, then later tonight in lingering SHRA a cold front will surge through the area, bringing gusty NW winds and IFR ceilings at the end of the 12Z TAF period.

DMX WATCHES/WARNINGS/ADVISORIES

None.