textproduct: Des Moines

KEY MESSAGES

- Hot and humid through the rest of the weekend, with heat peaking on Monday.

- Scattered thunderstorms across south central to southern Iowa this afternoon and evening. The severe potential is low, though an isolated severe storm cannot be ruled out in SE Iowa.

- More widespread thunderstorms are expected into Monday morning, and again into late Monday afternoon through the evening. Strong to severe storms are possible.

SHORT TERM /THROUGH MONDAY/

Issued at 243 PM CDT Sat Jul 18 2026

A look at surface features today shows an area of low pressure over the northeastern CONUS, while an area of weaker high pressure sits over the Northern Plains. Over Iowa, a boundary is draped generally from west to east across central Iowa, near the I-80 corridor, which did produce weak showers and storms through about mid-morning over northern to northeastern Iowa before tapering off. Much of northeastern Iowa received around a quarter to half inch of rain, with localized three-quarter inch values from this earlier activity. Thanks to this passing boundary to the north, temperatures so far are slightly cooler with values in the low to mid 80s, which may only increase a few more degrees this afternoon yet. Ahead of the boundary, temperatures are still expected to warm up to similar values as have been observed the last several days, with highs in the low to mid 90s. This boundary will also be the focus for the expected development of showers and thunderstorms into the late afternoon through the evening. Moisture convergence along the boundary will aid to lift parcels through a favorable environment characterized by instability values around 2500-3000 J/kg, though weak shear values around 10-15 knots and poor lapse rates will largely be working against storms from becoming strong/severe. There is a low possibility that a storm could produce a sub-severe and possible isolated severe gust over southeast Iowa where DCAPE values over 1000 J/kg are noted. Besides the potential for wind, efficient rainfall is possible during the extent of storms as they go up and quickly come down, given PWATS around 2 inches and warm cloud depths over 15 kts that could lead to rainfall amounts up to an inch or slightly higher. Outside of localized heavy rainfall with this activity, flooding is not a concern at this time.

While the aforementioned area of low pressure departs further east late tonight, the surface high will pass southeast into the Great Lakes, with the boundary moving into northern Missouri. A gradual decrease in instability and continued weak flow will lead to the waning of storm development and the overall return of dry conditions across the state. Overnight conditions will feature more comfortable temperatures in the 60s, paired with mostly clear skies. Cannot rule out localized patchy fog in low lying areas through sunrise. As the previously mentioned area of high pressure tracks southeast across the Midwest, the area of subsidence associated with it will cover the greater majority of Iowa, keeping much of the area dry with light southeast winds as highs reach into the upper 80s to low 90s, with similar heat indices given slightly lower dewpoints than yesterday in the mid to upper 60s. Wildfire smoke that has impacted areas further north and east of Iowa over the past several days will make it's way into portions of eastern Iowa through the day due to this shift in winds, before decreasing into Monday. However, the thicker smoke should generally remain east of the forecast area. Over southwestern Iowa, a lingering boundary and instability axis is indicated to be overhead, which could result in some development of isolated showers and storms into the afternoon to early evening timeframe, though the bulk of activity looks to generally occur over Missouri.

Into the start of the upcoming work week, a rather potent shortwave trough over Alberta/Saskatchewan Canada is progged to gradually shift southeastward across the Upper Midwest through Monday, which will shove the ridge westward of Iowa and therefore place the Central Plains into an upper level northwest flow regime. At this same time, low level west/southwest flow will increase into the area, resulting in the advection of warmer and more humid air into Iowa. In the morning, a boundary is expected to pass east/southeastward across Minnesota and into Wisconsin, where a decaying MCS is indicated to gradually track. There is a potential that this system passes through some portion of northern and northeast portion of Iowa during this period, with the main concern being damaging wind gusts as storms organize into a bowing segment, though small hail cannot be ruled out given the elevated nature of these storms. There is still uncertainty on the exact track of this system, so will have to keep an eye on later model runs and adjust per latest trends. Dry conditions are expected to return later in the morning through the afternoon, with the push of warmer and more humid air into Iowa leading to the hottest day in the forecast as highs are expected to push through the mid to upper 90s and dewpoints surge into the low to mid 70s across the forecast area. These conditions will result in widespread heat index values over 100 degrees, with heat headlines likely issued later this weekend as confidence continues to grow, so stay tuned. Those spending time outdoors should take frequent breaks in the shade and stay hydrated.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Issued at 243 PM CDT Sat Jul 18 2026

As the deepening shortwave arrives into the Upper Midwest into Monday evening, a cold front is expected to push into northern Iowa and gradually track southeast over the state. Stronger forcing for ascent and moisture availability will be present overhead, paired with aforementioned hot and humid conditions. This environment will feature high instability values over 4000+ J/kg and strong shear values over 50 knots, which will be more than favorable to produce organized convection capable of becoming strong to severe, where all hazards would be in play. As storms evolve into late Monday to early Tuesday morning, the development of another MCS is indicated that looks per model guidance to move across northern into eastern Iowa, with additional concerns for potential severe winds and heavy rainfall given very favorable PWATS around 2+ inches and warm cloud depths around 16 kft. More specific details will become more clear in the coming days, but planning for potential severe weather can start now by monitoring the forecast, having multiple ways to receive warnings, and altering plans as needed.

Showers and storms are expected to taper off after sunrise Tuesday, with surface winds shifting northwest as the mid-level trough and associated deepening low pressure system departs the region. A tightened pressure gradient on the backside of this system will bring breezy conditions through the day, with gusts up to 20-30 mph. Highs as a result will also be ''cooler'' with values in the 80s, and dewpoints in the upper 50s to low 60s. The pattern through midweek generally remains the same as the ridge remains west of the region and upper level northwest flow continues to bring slightly cooler and less humid conditions overhead, as highs generally top out in the 80s and dewpoints reach into the upper 50s to low 60s. Subtle waves riding the larger scale flow with periods of some level of moisture return though could bring additional chances of showers and possible storms to Iowa later Wednesday through Friday, though details are not as clear on exact timing and coverage details of this activity and will be refined in the coming days. More summer like conditions are expected to return near the end of the work week as temperatures gradually return into at least the low 90s as the ridge strengthens once again.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1238 PM CDT Sat Jul 18 2026

A boundary slowly sinking across Iowa this afternoon has led to some localized areas of MVFR conditions due to low ceilings at KFOD and KALO, but should improve over the next few hours, with a potential for similar conditions to arrive at KDSM and KOTM after 20-21z or so, but only for a short period. Otherwise, expecting storms to develop into south central to southern Iowa late this afternoon to evening, with KOTM possibly impacted and less confidence further north to KDSM, though trends will be monitored closely. Winds through the period are expected to remain light, shifting northeasterly tonight and then southeasterly towards the end of the period. Cannot completely rule out localized patchy fog around sunrise. Wildfire smoke moving into Iowa from the southeasterly flow late in the period may also bring in slightly reduced visibilities but still VFR conditions.

DMX WATCHES/WARNINGS/ADVISORIES

None.