textproduct: Des Moines

KEY MESSAGES

- Dangerous heat will continue to build over the rest of the weekend into early next week, with a Heat Advisory in effect today, and a widespread Extreme Heat Warning Sunday. An Extreme Heat Watch remains Monday for potential continued heat impacts.

- Severe weather is possible late tonight into Sunday morning, and again Sunday evening into Monday morning. The primary concerns are damaging winds, large hail, and heavy rain.

SHORT TERM /THROUGH MONDAY/

Issued at 301 PM CDT Sat Jul 25 2026

After a morning filled with rather widespread dense fog and stratus, conditions have greatly improved this afternoon, with satellite imagery showing no fog and skies gradually clearing of clouds over much of western and north/northeast Iowa. Due to the slow erosion of stratus through the morning, temperatures were also slow to increase in the 70s to low 80s, but since early afternoon with the increased clearing are now rising faster with values through the 80s, warmest west. The beginning of the well-advertised heat wave certainly has begun given the presence of the western thermal ridge and a strong push of low level theta-e advection into the state, with forecast highs still expected to top out in the upper 80s east, while in the low to mid 90s west, where the Heat Advisory remains in effect through the rest of today.

Late tonight into early Sunday morning, model guidance continues to signal a slowly decaying complex of elevated thunderstorms exiting South Dakota/Nebraska and entering west/northern Iowa, roughly where the increasing 30-40 knot low level jet is progged to be located and where an instability gradient is indicated. As this activity initially enters the state, the potential is in place for at least some isolated severe weather, given MUCAPE values around 2000-3000 J/kg and wind shear values around 30-40 knots overhead. The main hazard of concern would be damaging winds given drier low levels with DCAPE values over 1500 J/kg and steeper lapse rates around 7-8 C/km that could lead to hail concerns as well. PWATS around 1.5-1.75 overhead, along with notable warm cloud depths could also lead to heavy rainfall where stronger storms develop, with isolated rainfall amounts up to 1-1.5 inches, low concerns for back-building potential at this time but something to monitor. Storm coverage should decrease through the morning as this activity moves south and east, with dry conditions expected to return for all areas mid- late morning. Close monitoring on trends will be important this evening on storm potential and coverage during this time, hence only the addition of low PoPS further south and east through the morning hours, with the potential for increasing these values if confidence increases.

Despite the potential for showers/storms in the morning and cloud cover, the further eastward movement of the thermal ridge Sunday will allow for more widespread heat impacts across the forecast area as stronger warm air advection moves into the region. Rather uncomfortable overnight lows through the 70s will be followed by a gradual increase in temperatures, especially into the afternoon as skies clear, resulting in highs topping out in the mid to upper 90s. These temperatures, along with forecast dewpoints in the upper 70s overhead will lead to widespread heat indices in the 105-110 degree range across the entire forecast area, making for a very hot and humid day. The Extreme Heat Warning therefore stands, which is in effect from 11am to 9pm Sunday. Those planning to spend time outdoors should limit time in the sun, taking frequent breaks and staying hydrated.

Sunday evening into Monday morning will feature the next potential for another window of shower and storm activity over the region. Guidance continues to indicate a more robust area of thunderstorm activity from a passing weak shortwave riding the ridge into the Upper Midwest, particularly over Wisconsin and Illinois where less influence of the cap further west and closer proximity to the mid- level feature is indicated. Forcing aloft during this time frame is more notable and the LLJ surges further into portions of Iowa and Minnesota, where deterministic models are now suggesting another MCS developing over eastern Nebraska/South Dakota into western Iowa, and tracking east southeast across the state through the morning hours. Favorable instability and shear profiles overhead will support another potential for severe weather, though lesser certainty is in place given more of a presence of the strong cap over these areas. If storms do develop, damaging winds and large hail would again be possible given dry low levels and steep lapse rates. Heavy rain is also in play with this activity into Iowa, given PWATS around 2-2.25 inches and a tall, skinny CAPE profile. Refinements are expected to continue with future forecast updates into Sunday.

If storms do move across the forecast area into Monday morning over a larger portion of the forecast area, the potential for continued widespread heat impacts could be limited somewhat. However, this would likely at most be a few degrees less for highs in spots where storms linger the longest and clouds remain. For now, maintaining forecast highs in the mid to upper 90s and heat indices over 100 degrees in most areas, with no change in the Heat Watch given this lingering uncertainty.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Issued at 301 PM CDT Sat Jul 25 2026

As the aforementioned trough deepens as it tracks over the Great Lakes into the Ohio valley late Monday into Tuesday, will see a push of cool air advection into Iowa that will end the stretch of sweltering heat. While temperatures will only be a touch cooler in the upper 80s to low 90s Tuesday, drier air from this shift in low level flow turning northwesterly will allow for slightly lower dewpoints in the upper 60s for most areas. The western thermal ridge overall will move very little through much of the work weak, with any precipitation chances signaled to largely remain west of Iowa until around Thursday, when a more potent shortwave dives southeast on the eastern fringe of this ridge from the Dakotas into Iowa. Certainly room for slight shifts in these larger scale features to occur in the coming days given this being further out in the forecast period, so stay tuned for updates. Highs through the rest of the week remain generally in the upper 80s to low 90s, paired with dewpoints in the 60s, more towards normal summertime averages.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1243 PM CDT Sat Jul 25 2026

Stratus has been stubborn to clear this afternoon, so have continued to delay return to VFR. Fog may develop again in the east tonight, but there will be challenges with clouds tonight, so left it as BCFG.

Speaking of clouds, the main forecast challenge this period is the thunderstorm potential tonight. There will be a complex moving across northern Iowa after 06z, diving southeast with time. Uncertainty remains in its intensity, with most guidance suggesting it will decay into scattered showers by the time it nears a terminal. No precipitation is mentioned right now as confidence is below 30%, but highest confidence right now is at KMCW.

DMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until noon CDT Sunday for IAZ004>007-015>017- 023>026-033>037-044>048-057>060-070>073-081-082-092-093. Extreme Heat Warning from noon to 9 PM CDT Sunday for IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097. Extreme Heat Watch from Sunday evening through Monday evening for IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097.