textproduct: Des Moines

KEY MESSAGES

- Our slow warmup continues each day this week, with actual temperatures in the low and possibly mid 90s. Heat indices may approach 100 at times, particularly mid to late week.

- Shallow, patchy fog possible early this morning, particularly in southeast Iowa.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 246 AM CDT Mon Jul 13 2026

High pressure and subsidence dominates across the central US this overnight as revealed by GOES channel 13 with a near perfect circle of clear skies from Colorado to Indiana. The sfc high is sitting over southeast Iowa, and the most calm winds are expected there tonight into early this morning. Radiative cooling is well on track currently, and brings in another sunrise timeframe with patchy fog potential. The near term forecast is quite similar to last night's conditions that produced some shallow patchy fog in north and west Iowa. However, calm winds may be more favorable in southeast Iowa this time. Fog is not expected to be widespread, but some low lying portions of southeast Iowa highways could see steep visibility reductions until 7am. Similar conditions are possible Tuesday morning.

Surface heating should have no issues recovering through the day today. Highs may be somewhat uniform across the state for today and tomorrow, though it will be a balancing act of a couple factors. 850mb temps will be a bit warmer across the north, where westerly winds dominate and remnants of an EML clip our CWA. However, this sits above an area of the state that has better soil moisture, and like yesterday is expected to retain higher dewpoints which may reduce the ability to mix down the warmer 850mb temps. In central and southern Iowa, dewpoints and soil moisture may be just a tick lower, and allow extra heating to match or exceed that in northern Iowa. Highs Tuesday will increase by a few degrees more as the stagnant airmass is heated further.

As far as dewpoint forecasting over the next few days, pick your favorite boundary layer scheme, models are all over the place. The dewpoint near DSM for example is anywhere between 60 and 75 across the model suite Tuesday afternoon. Expectation is that widespread evapotranspiration will be enough to counter mixing down of fairly dry mid-levels. Most areas will keep mid 60s dewpoints, even at peak heating, and areas with better soil moisture, crop maturity, and reduced turbulent mixing will break into the 70s. Regardless, this is generally too low to have a large effect on heat indices. Therefore, headlines will not be needed in the short term. However, wet bulb globe temperatures will be near 85 on Tuesday given heat, lack of breeze, humidity, and ample sunshine. So, despite not meeting heat headline criteria, the middle of the afternoon, particularly Tuesday, will be a sweltering time to be doing work or exercise outside.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 228 PM CDT Sun Jul 12 2026

A Canadian long wave trough will dig southeastward into the northeastern CONUS through mid- to late- week, which attempts to shunt the 500 mb ridge overhead back to the west. As this occurs, the surface high pressure will begin to weaken, transitioning us to a more transient surface pattern over Iowa. This increases the spread in temperature solutions among deterministic and ensemble guidance through the end of the week. The general trend seems to be continued warming into the weekend, although NBM may be running too hot with forecast highs in the mid 90s and dewpoints in the 60s. Should dewpoints increase into the 70s, highs would likely be closer to the low 90s. Adjustments have been made to the forecast to account for this, but will need to continue to monitor trends. In addition to temperatures, the weakening high and increased moisture Thursday into Friday may bring back rain chances to the state. This is a low confidence scenario, especially with the late week pattern still in flux, so the forecast remains dry at this time. Severe chances will be better assessed in the coming days, but weak flow should help mitigate severe chances through this period.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 621 AM CDT Mon Jul 13 2026

VFR conditions will prevail through the TAF period. Some potential for fog exists tomorrow morning, but conditions may be less favorable than this morning which produced only briefly patchy fog at KFOD.

DMX WATCHES/WARNINGS/ADVISORIES

None.