textproduct: Des Moines

KEY MESSAGES

- Hot and humid conditions will persist through this weekend. The heat index will peak in the upper 90s to near 100 degrees each day.

- Isolated thunderstorm chances return on Thursday and Friday. The threat of severe weather is low.

SHORT TERM /THROUGH THURSDAY/

Issued at 104 AM CDT Wed Jul 15 2026

Iowa will remain smothered beneath a deep-layer ridge for the next several days. The result will be persistent heat and humidity, and little has changed in forecast thinking in that regard. Only slight adjustments to temperatures and dewpoints have been made, and heat index values will still peak around the upper 90s both today and Thursday. Meanwhile, we are once again seeing patchy fog develop early this morning due to the combination of high surface dewpoints, calm winds, and clear skies. Some high-res guidance suggests the best dense fog chances will reside in our northern and western counties around sunrise this morning, with somewhat higher coverage than Tuesday morning. However, with an expectation that any visibilities below 1/4SM will be spotty and transient, no advisory has been issued at this time. Observations will be closely monitored through sunrise.

One feature of note is a slight weakness in the 500 MB ridge, lying to the south of the surface ridge over AR/MS/TN at this time. There are slight ripples of enhanced 500 MB vorticity in this area, along with deeper moisture content, resulting in greater cloud cover and some showers and thunderstorms. Forecast models are unanimous in drifting this feature northward into Missouri later today and tonight, then to some extent into Iowa on Thursday. However, it will be weakening during this time and a reorientation of the 500 MB ridge will also cause it to turn more northeastward. The result is that any impacts in Iowa will most likely be confined to about the southeastern half or so of the state, where isolated to scattered thunderstorms may occur Thursday and Friday before the area shifts away to our east. Have thus kept POPs low on Thursday, but expanded their coverage a bit to indicate slight (20%) thunderstorm chances in our central, southern, and eastern counties during the afternoon and evening hours. Given the complete lack of flow/shear and weak forcing, it is anticipated any convection that does occur will be in the form of "airmass" or "popcorn" storms with a low threat of any severe weather.

Finally, widespread smoke from wild fires in Canada has been advecting east southeastward over Lake Superior, around the northern periphery of the 500 MB ridge that stretches from the Midwestern U.S. down into the Ohio River valley and Appalachian Mountains. As the ridge becomes somewhat pinched off in the next few days but doesn't really shift much southward it appears the smoke will make some inroads and sink over Michigan, Wisconsin, and parts of Minnesota by tonight and Thursday. However, indications are that it should remain northeast of our area through Thursday.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/

Issued at 250 PM CDT Tue Jul 14 2026

The upper level pattern begins to transition through the second half of this week and through the weekend, as a long-wave trough digs in over the northeastern CONUS. The upper ridge overhead will begin to modify and translate back westward as this occurs, but still generally remains overhead through the end of the week. The result will be continued warm temperatures, but slight changes to the low level moisture and flow patterns. First, we'll see the surface high pressure begin to weaken and low-level flow become more south to southwesterly. This will bring warmer 850 mb temperatures from the plains eastward into Iowa, leading to warmer surface temperatures. The warmest day looks to be Friday, as highs climb into the mid to upper 90s with widespread heat indices near or exceeding 100F. As mentioned previously, depending on how heat indices play out Wednesday and Thursday, heat headlines may be needed later in the week as we see multiple days of near or above 100F heat indices Friday and into the weekend.

The more south to southwesterly flow will also allow for more low to mid-level moisture to be transported back into the area. With the better layer moisture and less subsidence from the high pressure, the potential for diurnally driven showers/storms returns later Thursday and again on Friday, primarily over southern and eastern Iowa. Instability will be plentiful, as is typically the case this time of year, but shear will be very low due to the weak flow through the layer. Therefore, any storms will be just general, pulsey thunderstorms with a low severe risk. Our ridge continues to push westward into the weekend, bringing us more into a northwest flow pattern. Shortwaves passing through this pattern will bring additional precipitation chances to end the weekend and into early next week.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 615 AM CDT Wed Jul 15 2026

Patchy fog has formed once again early this morning, but will dissipate by 12Z or very shortly thereafter. It may occur again Thursday morning, but again will be patchy and transient, with confidence in occurrence at any given location and time too low to include in the TAFs at this range. Aside from fog considerations, no aviation impacts are anticipated with nearly clear skies and very light winds.

DMX WATCHES/WARNINGS/ADVISORIES

None.