textproduct: Des Moines

KEY MESSAGES

- Thunderstorms will fester over the area through the day.

- Stronger storms are expected to develop this afternoon, and are most likely in southern Iowa. These storms primarily pose a hail, wind, and flash flooding threat.

- Pleasant weather returns on Sunday.

SHORT TERM /THROUGH SUNDAY/

Issued at 301 AM CDT Sat Jun 13 2026

A complex severe weather setup looks to unfold today. Looking across the CONUS, the main shortwave later to be responsible for today's storms is still over Montana but will pivot east quickly in the coming hours. A more subtle shortwave is visible in RAP analysis and mid-level water vapor over southern South Dakota and western Nebraska. A deepening surface low sits over eastern Colorado, with a cold front extending NE to the Great Lakes and across NW Iowa. Ahead of the surface low a LLJ is already reaching 40 knots and may continue to strengthen overnight, with the nose aimed at eastern Nebraska, though the LLJ will fade in strength after 12z. 3000 J/kg MUCAPE and 1300 J/kg DCAPE is advecting north quickly out of Kansas riding the LLJ.

CAMs are in decent agreement about LLJ induced elevated CI in eastern Nebraska near 09z, though there is significant uncertainty in eastward advancement into Iowa. A long-lived MCS is unlikely as the fading LLJ will orphan the storms as they move east. So the damaging wind threat will be minimal though perhaps non-zero given some nearby strong DCAPE values. Per the new SPC outlook, the hail threat is the largest threat with the morning convection given MUCAPE of 3000+ being advected in, though shear looks messy and marginal overall. How far this complex of storms can advance east will have implications for our severe weather threat today. Given the 00z CAM suite and recent HRRR trends, it is likely an outflow boundary (OFB) is draped out behind the morning convection. As a most likely location of this boundary by early afternoon, REFS guidance places it west/east over far southern IA.

Three separate airmasses may be in play for the IA slight risk today. 1. Air unmodified by outflow. At least 2000 SBCAPE and fairly unidirectional shear profiles. 2. Air in the residual cold pool but ahead of the cold front. Better backed low level winds but poor lapse rates. Perhaps some airmass/SBCAPE recovery with intermittent sunshine before the cold front passes. 3. Near the OFB mid afternoon (likely near our southern border). Latest CAM trends show better backed surface winds and sufficient effective shear for supercells. Additionally, airmass recovery may be sufficient for moderate to strong SBCAPE/3CAPE.

The most likely scenario today appears to be morning storms across western and central Iowa with a low-end hail threat. Elevated storms may continue to percolate in the residual outflow and increase in coverage by mid afternoon as the cold front passes with a wind/hail threat where the best airmass recovery occurs. The most robust supercells with primarily wind and hail threat (and maybe a tornado if everything comes together) may occur on the OFB likely draped out in southern IA or Missouri, though this boundary could advance fairly far south without much low-level flow to resist the cold pool. It is worth noting recent HRRR runs where the OFB is perfectly positioned for discrete supercells across central to southern Iowa, with strong CAPE and well curved hodographs. This is a less likely scenario, though given the way it is initializing it is admittedly not "off its rocker" yet so to speak. As a continuation of previous AFDs, a flash flooding threat remains as well. Isolated areas of several inches of QPF are present in the CAMs, especially in southern Iowa where the ground is already very saturated.

High pressure and cold air advection fills in on Sunday behind the front. It should be a very pleasant day with clear skies and highs in the low to mid 70s. Downward momentum transfer via PBL mixing will make winds gusty at times, especially in northern Iowa.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Issued at 243 PM CDT Fri Jun 12 2026

Cooler temperatures are forecast Sunday night through the end of next week. Much of the area will stay below 85 degrees each day, with a slight warming trend towards the end of next week. Lows Sunday night into Monday will bottom out in the high 40s to low 50s before gradually warming each night. The overall pattern looks much less active, save for a few passing shortwaves. Specifics on those will be addressed in the coming days.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1229 PM CDT Sat Jun 13 2026

Messy aviation forecasts today as a cold front crosses Iowa. Several areas of storms are ongoing and more are expected to develop this afternoon. Tried to time various rounds and areas of showers and storms; however confidence is low in the specifics at any particular location. Ceilings are mainly VFR except for OTM which is still ahead of the front and has MVFR ceilings.

DMX WATCHES/WARNINGS/ADVISORIES

None.