textproduct: Des Moines

KEY MESSAGES

- Temperatures will fall into the 30s across northern Iowa this morning, and near freezing in some areas. A Frost Advisory remains in effect generally north of Highway 20.

- Shower and thunderstorm chances return late Monday night into Tuesday. A few stronger storms could develop in southeastern Iowa on Tuesday afternoon, with gusty winds being the main concern.

- Breezy conditions are forecast on Tuesday, especially in northern Iowa during the afternoon where northwest winds of 25-30 MPH with gusts to 40 MPH or more are likely.

- Warmer temperatures are expected through much of the week and into next weekend.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 220 AM CDT Mon May 11 2026

A large surface high pressure area is draped across the region early this morning, centered over Minnesota into Wisconsin but certainly extending through Iowa as well. The result is very light north to northeast breezes across our service area. An area of mid-level clouds has persistently developed over about the southern half of Iowa on the periphery of the ridge, limiting radiational cooling in that area with temperatures largely remaining in the 50s as of this writing. However, across northern and eastern Iowa where skies are clear, temperatures have already fallen into the 40s and will fall farther before sunrise, especially in spots where winds go calm. Lows generally in the 30s are still expected in those areas this morning, and the Frost Advisory remains in effect for our northern counties roughly north of Highway 20. The clouds in the south will gradually clear out this morning, but even in those areas that clear before sunrise temperatures will not be able to fall as far as in the north.

During the day today the surface ridge will move off to our east over the Great Lakes, allowing for a return of south southeasterly low-level flow by late in the day. Concurrently, a modest mid-level thermal ridge will move over the High Plains and toward Iowa by this evening, combining with the low-level wind change to support warmer temperatures with highs this afternoon ranging from upper 60s in our northeastern counties to near 80 in the southwest. Satellite imagery does show cirrus clouds approaching from the northwest which may affect our area today, however, indications are that these will be quite thin and not significantly mitigate the combined warming effects of the synoptic pattern and a seasonally high solar angle.

From late tonight into Tuesday night, our primary feature of concern is the 500 MB trough that will be digging from far southern Canada later today, down into North Dakota and Minnesota tonight, then across Iowa and the Great Lakes region Tuesday and Tuesday night. This system will push an attendant surface trough southeastward through Iowa on Tuesday, which will have several impacts on our sensible weather. Ahead of the boundary, tonight, low-level winds will turn to south and eventually south southwest and gradually increase overnight, supporting much warmer nighttime temperatures. Whereas lows this morning will range in the 30s north to 40s south, on Tuesday morning they will range in the 50s northeast to near 60 southwest. Also, with the 500 MB trough approaching late tonight broad forcing for ascent will spread overhead along its leading flank, combining with the low-level warm air advection to support scattered showers ahead of the surface boundary, particularly in our northeastern areas. Chance PoPs (30%) are maintained in those areas for the expectation of scattered light showers after midnight and into the early morning hours Tuesday.

The precipitation outlook during the day Tuesday becomes more uncertain. Most upper-level support will translate eastward away from our area during the day, however, the surface boundary will be moving through in the late morning (north/central) to late afternoon (southeast) hours, with diurnal destabilization occurring ahead of it. Forecast soundings depict a stout mixed/dry layer with a weak capping inversion above it, and with limited surface convergence along the boundary or forcing aloft, there may not be sufficient impetus for initiation for most of the day. However, most CAMS include scattered light echoes filtering through during the day, which likely indicate light elevated showers based above the mixed layer. Whether any such showers will be able to precipitate through that layer to the surface remains to be seen. By the afternoon, in our southeast, if the cap can be overcome and moisture is sufficient then we may be able to generate a few thunderstorms in our southeastern counties just before the boundary pushes through, which would carry some threat of strong wind gusts given the steep low-level lapse rates, but that is a conditional threat. For now, have maintained 20-30% PoPs in our central and southeastern counties during the day to account for this scenario.

In addition to precipitation potential, the passage of the surface trough on Tuesday will also bring strong winds to the area, especially in northern Iowa where confidence is high in blustery conditions by the afternoon. A deep well-mixed layer with dry adiabatic lapse rates up to 700 MB and homogeneous northwest winds of 25-30 KT or higher within that layer support surface winds approaching 30 MPH, with gusts to 40 MPH or higher at times and advisory criteria could be met. Relative humidity will fall to around 20% in many areas and combined with the strong winds this could support elevated fire weather concerns, however, these are heavily mitigated by the greenness of most surface fuels. Even so, Tuesday will not be a conducive day for outdoor burning.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 248 PM CDT Sun May 10 2026

Temperatures cool slightly on Wednesday, albeit still in the 70s. The broad upper level ridging then fills in behind the departing shortwave, warming temperatures into the 80s through the second half of the work week. As mentioned in yesterday's long term discussion, despite the brief ridge moving in, the pattern quickly becomes agitated through the end of the week and into next weekend with multiple shortwaves and increasing shower and thunderstorm potential, the first of which looks to be on Thursday night into Friday as a healthy gulf moisture stream returns to the state. Additional chances continue into the weekend. This will likely put a damper on the highs in the 90s that NBM guidance had been forecasting for next weekend and today's extended forecast now reflects this a bit better. That said, with the southwesterly to westerly flow pattern, temperatures should stay seasonably warm in the 80s through the weekend.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1142 PM CDT Sun May 10 2026

VFR conditions are expected to prevail at all sites throughout this TAF period. Timing was refined with regards to the wind shift expected to take place throughout the day tomorrow. As the surface high pushes to the east, winds will go from light and variable to being from the south at around 7kt. Towards the end of the period, winds are expected to increase to 10-15kt across northern sites and beyond the end of the period winds may increase at sites farther south.

DMX WATCHES/WARNINGS/ADVISORIES

Frost Advisory until 8 AM CDT this morning for IAZ004>007- 015>017-023>028-039.