textproduct: Des Moines

KEY MESSAGES

- Warm and dry conditions today through at least mid-week. Highs in the upper 80s and 90s this week.

- Shallow, patchy fog possible early this morning and again Monday morning.

SHORT TERM /THROUGH TUESDAY/

Issued at 254 AM CDT Sun Jul 12 2026

A rather stagnant weather pattern is in store over the next several days. Heat will continue to increase and precipitation chances remain low through this period. The H500 ridge continues to build across the Rocky Mountain West, positioning us under overall weak flow as the main jet stream is being routed up and over the building ridge into Canada. Surface high pressure will continue to build this morning, and should bring in weak and a relatively dry airmass. This and height rises have cleared out any attempts at cloud cover this morning. The most pressing near term challenge is whether to expect any radiation fog as we approach sunrise. It appears the calm winds and clear skies may be countered by quite shallow moisture. Fog may still be possible for a short time around sunrise, but it is expected to be patchy at best. Similar conditions will return Sunday night.

The pattern over the next three days has very little variation. The surface high stalls over Iowa while the thermal ridge builds over the Dakotas. Sfc-850mb flow will continue to be weak, meaning advection is minimal and we will just be modifying the same airmass each day. 850mb temps will be slightly warmer today, and again on Monday, but the warmer >25C temps look to remain west and north of Iowa, sparing us from a true heat wave, at least for now. Still, the ample sunshine is expected to warm the temperatures a couple degrees more each day. NBM suggests highs just below 90 today, 89-92 tomorrow, and 91-94 Tuesday.

For the sake of headline discussion, it is worth diving into humidity expectations as well. The lethargic synoptic pattern won't do much to advect more or less moisture into Iowa, and afternoon Tds will become almost entirely dependent on mixing, soil moisture, and evapotranspiration (ET). Corn is nearing maturity and ET is becoming more significant each day, which may keep dewpoints at least in the 60s each day across most of Iowa. Secondly, NASA SPoRT shows soil moisture is highest across NE Iowa with some pockets into SE Iowa. It will be most favorable to retain low to mid 70s Tds in these areas (lower Bowen ratios) and directly beneath the sfc high where turbulence is lowest for overall less mixing out. These Tds would be high enough to adjust the apparent temps up a few degrees, but this will be countered by decreased heating in these areas. By Tuesday we may be at borderline headline criteria, particularly in eastern Iowa, but uncertainty in humidity will make this a later decision.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Issued at 225 PM CDT Sat Jul 11 2026

The warm and humid conditions generally stick around through the remainder of the week, although the influence of the surface high and upper ridging begins to weaken through the second half of the work week. An amplified Canadian trough will begin to push the 500 mb ridge back westward, putting Iowa on the periphery between the northwest flow to our northeast and ridging to our west. At the surface, this will equate to a messy surface pattern with weak high pressure overhead and low pressure to our west, favoring south southwesterly flow. This transition will take place Wednesday and Thursday, ultimately not resulting in much noticeable change at the surface aside from continued warming both days. Highs are expected to reach the mid-90s with dewpoints around 70, pushing heat indices into the upper 90s and near 100F. With the weakening high, subsidence also won't be as strong and the potential for diurnally- driven thunderstorms could creep back into the forecast through the second half of the week. With the lack of any prominent systems, guidance and NBM are struggling to resolve this, but a signal does exist when looking at the longer range models. There's of course no shortage of instability this time of year but the flow in this regime should be fairly weak, so the severe risk appears low at this time. With the low uncertainty, the forecast remains dry through mid-week, but will be something to watch for as we get closer.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 637 AM CDT Sun Jul 12 2026

Aside from patchy fog currently clearing out across the state, VFR conditions prevail today through tonight. The fog this morning was rather isolated, but still resulted in brief LIFR conditions at KMCW. Similar conditions may be in place tomorrow morning, but confidence is too low to include in this issuance.

DMX WATCHES/WARNINGS/ADVISORIES

None.