textproduct: Des Moines

KEY MESSAGES

- Heat continues this week with highs in the lower to mid 90s. The afternoons will still feel quite hot despite being below headline criteria through Wednesday.

- Heat indices near 100F and thunderstorm chances become more likely by late week.

- Shallow, patchy fog possible early this morning, particularly in central and eastern Iowa.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 247 AM CDT Tue Jul 14 2026

The 600 decameter ridge is currently sitting over southern MN and northern IA where it will generally stall out over the next several days. Flow is quite weak in the low levels, though stronger 850mb flow exists on the ridge periphery in northwest Iowa and rare easterly 500mb flow is over 30 knots. With subsident clear skies, radiative cooling is well underway this AM, and perhaps ahead of schedule at a few sites in eastern Iowa. This could lead to some patchy fog in low lying areas, similar to what has been observed the last several nights. Some fog is already being observed in central and eastern IA river valleys as of 7z. Conditions will be similar again tomorrow morning. All fog should burn off by 7am.

This week may be a rare instance where persistence forecasting is fairly effective. Changes to positioning of the sfc high/sky coverage/warmest 850mb temps will be insignificant. Yesterday's highs stayed below 90 excluding the DSM heat island, which puts the NBM forecast from this time yesterday about 2 degrees too high. Therefore, lowered forecast highs for today by a degree or two. NBM dewpoint forecast actually tracked well, mixing into the mid to upper 60s during peak heating. This lends some confidence in the nearly identical heat indices forecast for Wednesday. Sure, we may be continuing to evapotranspirate in additional shallow moisture today/tomorrow, and highs may continue to increase a couple degrees, but given yesterday's obs we certainly aren't trending towards the higher end solutions in the short term. The only noteworthy difference to Wednesday's forecast is the development of cumulus given a better moistened 850mb layer.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 226 PM CDT Mon Jul 13 2026

The dry spell is expected to continue through at least the latter half of the week as a deep ridge continues to dominate the midwest. Highs by the end of the week will top out in the mid 90s with dew points pushing the upper 60's to lower 70's. The primary source of the surface moisture will be crop evapotranspiration; due to a lack of external moisture advection, dew points should cap out in the lower 70s on Thursday.

Southwesterly flow returns to central Iowa toward the weekend, bringing a push of deeper moisture to the area. Highs will remain in the mid 90s with dew points creeping just above 70 degrees. Friday and Saturday currently offer the highest probability for heat indices over 100 degrees, though values are still forecast to remain below headline criteria. However, multiple days of heat indices nearing 100F and little relief with overnight lows in the mid 70s may warrant heat headline discussion later this week. Additionally, a passing shortwave interacting with this deeper moisture will bring a chance for scattered showers and storms Friday afternoon and night. Severe weather is unlikely due to minimal vertical wind shear, so any storms that develop will be pulse-like in nature.

For those looking for a break in the heat, model guidance hints that the powerful ridge will shift south and west by Sunday, allowing for northwestern flow to enter Central Iowa. Model guidance also suggests that organized convection will be possible Sunday and onward. Convective trends will be something to watch as we near the weekend.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1033 PM CDT Mon Jul 13 2026

VFR conditions will prevail through the period. Patchy fog is possible overnight in eastern Iowa, however impacts will be isolated if it develops and have not included in TAFs at this time. Most likley area for fog development would be in eastern Iowa near KALO/KOTM or the river valley near KFOD.

DMX WATCHES/WARNINGS/ADVISORIES

None.