textproduct: Des Moines

KEY MESSAGES

- Warm temperatures continue to start this week with highs in the mid 80s to near 90 today and Wednesday. Brief cooldown mid-week with highs still in the low 80s through end of week.

- Shower and storm chances (20 to 30%) are expected late this afternoon into the evening and again late Wednesday, both over northern Iowa. The severe risk is low, but gusty winds and hail are possible.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 210 PM CDT Tue May 26 2026

The current pattern across the central US is characterized by relatively weak flow through the mid and low levels and a stagnant jet pattern. A zone of ridging is sitting over Iowa as the divider between the near-stationary 500mb closed lows over the US west coast and Quebec. Sunny skies and warmer temperatures spread across the state this afternoon, but locally higher theta-e exists in the northern part of the state. A weak surface trough/diffuse windshift boundary over central MN was likely enhanced by remnant overnight convection. This boundary will sag south and west over the next 24 hours, driven by a strengthening high over Lake Superior. This boundary may provide enough of a trigger for a few thunderstorms in northern Iowa. SFC CAPE on the order of 1000-1500 J/kg will be enough to sustain a few short lived, single cell updrafts, but only around 20 knots of effective shear will not support storm organization. Still, relatively dry low levels yield DCAPE values near 1000 J/kg that could lead to strong downdrafts in collapsing cells.

Showers and storms may continue to bubble along and near the windshift boundary overnight, but should clear out around sunrise. Mostly sunny conditions will be in place for much of the day, allowing for another dry, well-mixed PBL. Despite the mixing, winds should stay quite weak, as there is very little additional momentum to mix down. The diabatic heating and efficient mixing will put high temperatures in upper 80s and possibly lower 90s in some locations. NBM/REFS mean temps for Des Moines sit around 89 degrees, but the 75th percentile is 92 and may be a realistic upper bound for highs tomorrow for the central part of the state. Despite the meager moisture, the heating again brings 1000-2000 J/kg of CAPE. The weak surface trough/wind shift boundary is expected to be sitting over the northern half of the state and may be the focal point of a few scattered storms during the afternoon and early evening. Severe weather is unlikely at this time, as effective shear will again be very low. However, dry low levels and high DCAPE values will create a potential for strong downdrafts in the stronger cells that develop. For storms today and tomorrow, QPF will generally be less than 0.2 inches.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 210 PM CDT Tue May 26 2026

On Thursday a weak low will eject east off of the much larger cutoff upper level low that has settled across California and the SW US. This weaker low will lift into the central US, taking advantage of Gulf moisture transport. The low level jet is oriented away from the area, though some convection may skim into southwest Iowa with weak instability, around 500 J/kg MLCAPE. There is very little shear, under 20 kts, to organize storms so any that do develop should be disorganized and pulsey in nature. The upper air pattern is largely unchanged into the weekend with a plume of instability from the Gulf and through the plains, skimming western Iowa. This will provide a window for diurnal thunderstorm development each afternoon and evening along this axis through Friday and the weekend. Sunday and especially into Monday the surface high east of the area builds back, helping to keep push thunderstorm chances west of the area and keeping Iowa dry. At this time guidance suggests that this will remain in place through early next week.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1234 PM CDT Tue May 26 2026

VFR conditions will prevail for most of the TAF period. A few thunderstorms in southern Minnesota may sink south into northern Iowa this evening and overnight. These scattered storms could impact KMCW first this evening, then later reaching KALO overnight. At this time confidence is lower in storms sinking far enough south into Iowa, so have maintained the prob30 groups at both sites. Wind becomes light and variable through Wednesday morning.

DMX WATCHES/WARNINGS/ADVISORIES

None.