textproduct: Des Moines

KEY MESSAGES

- Thunderstorms are likely (60% or greater chance) across northern Iowa later this morning, with some chance (30-40%) farther south toward central Iowa. Any storms will carry a threat of severe weather, primarily in the form of strong winds but with hail also possible.

- A prolonged period of hot, muggy, oppressive weather will begin Sunday and will likely continue through the coming week and potentially the Fourth of July weekend. An Extreme Heat Warning is in effect for the entire area, beginning this afternoon except in northeastern Iowa where it begins on Monday.

- Additional storm chances are possible Monday evening into Tuesday and again at times midweek.

SHORT TERM /THROUGH MONDAY/

Issued at 130 AM CDT Sun Jun 28 2026

The forecast of convective evolution and potential for today has changed significantly since last night. Thunderstorms have developed more extensively and farther south along the SD/NE border and high-res/CAM guidance has been playing catch-up for the last six hours or so. Some solutions still aren't initializing correctly with the ongoing storms and even those that are move the complex essentially due east across southern MN and northern IA later this morning. This is consistent with the expectation of the nose of a nocturnal LLJ currently over eastern Nebraska pivoting slowly eastward near the IA/MN border over the next 6+ hours. However, the same jet is pushing a considerably warmer and more humid airmass up into our area (prompting the heat headlines and ushering in the well- advertised heat wave for this week), and just ahead of this airmass there is a ribbon of enhanced instability that will push into Iowa overnight. By 12Z this instability axis will stretch from the northwestern to southeastern portions of our CWA and depending on how the cluster of storms and its attendant cold pool evolve, the storms may turn southeastward into the instability and reach central Iowa after sunrise. In any event, have increased to likely (60-70%) PoPs across our northern counties and carried chance (30-50%) PoPs as far south as Highway 30/I-80 or so. Wherever the storms do move through they will carry a threat of gusty winds that could be severe, given the 50+ KT of deep shear and 1000-14000 J/KG of DCAPE predicted to accompany the system. Potential gust magnitude will depend on the evolution and balance of the cold pool and any descending rear inflow, but overall the threat should gradually increase as the storms move eastward across our area, likely exiting our northeastern/eastern counties by around noon.

Aside from the convective forecast for this morning, the big story remains the oppressive and persistent heat that will blanket the region for most or all of the coming week (or longer). This forecast remains on track, although temperatures might under-achieve in our north today depending on how this morning's storms evolve and how quickly any cold pool they leave in their wake retreats or washes out this afternoon. Either way the heat will build in today, and even in the north by tonight and Monday as the large southeastern U.S. 500 MB ridge exerts its influence further into Iowa. The Extreme Heat Watch has thus been upgraded to an Extreme Heat Warning for our entire forecast area, beginning early this afternoon except in our northeastern counties where it will begin at noon Monday.

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

Issued at 245 PM CDT Sat Jun 27 2026

The upper level pattern changes very little through the early work week, with the longwave trough across the western CONUS becoming centered over the Desert Southwest, while the extra-tropical high lifts further north into the Ohio Valley and associated heat dome expands across much if not all of the eastern and central CONUS. Excessive heat will continue to impact all of Iowa, as forecast highs are expected to top out each day into the mid to upper 90s, paired with heat indices up to 110 degrees. Given the expectancy of this oppressive heat over several days and little recovery overnight as lows repeatedly only ''cool'' into the 70s, the Extreme Heat Warning is warranted to continue at least through Tuesday were confidence remains on the higher side, again with the likely expansion of this headline to include the entire portion of the DMX forecast area. Safety measures as discussed above need to remain in practice to avoid negative effects of this conditions that can quickly become dangerous. Outside of this heat, another area of developing surface low pressure is expected to lift northeast across the Central Plains, with an associated boundary moving into northwest Iowa by Monday evening. While deterministic models generally agree on the general area of this boundary, the extent of development of showers and storms remains more uncertain given lack of moisture above the more stable near surface layer. Any storm development that can occur would generally hold concerns for large hail given high instability and steep lapse rate profiles, along with gusty winds into Tuesday morning. The Slight Risk per SPC remains over northwest Iowa given this potential, with at least slight adjustments anticipated over the coming days. Additional chances of evening/overnight convection are signaled again Tuesday night into Wednesday, though confidence is lower to discuss coverage and intensity details in this forecast package, given this is still days away but worth keeping an eye on.

Above average temperatures are expected to remain in the forecast into the mid-late week period, with current forecast highs generally in the low to mid 90s and heat indices over 100 degrees. The expansion of heat headlines will be assessed beyond Tuesday in the coming days, with the likelihood of expansion quite probable. Additional chances for showers and storms are also indicated as a few shortwaves as suggested per long term guidance pass through within a growing area of upper level ridging over the Central Plains and Midwest, while a troughing pattern generally remains across the western CONUS.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1257 PM CDT Sun Jun 28 2026

Low clouds continue to bring MVFR conditions across the forecast area this afternoon, with more isolated IFR conditions over northern Iowa. Spotty showers are also tracking near KALO and will remain in the area over the next hour or two, until conditions dry out across the terminals. Should see ceilings gradually lift above 3 kft within the next 3-6 hours, leading to the return of VFR conditions for the rest of the period. Otherwise, winds will remain breezy but decrease slightly into the evening and through early Friday, though LLWS is expected to develop across KFOD, KDSM and KOTM after 00z before fading beyond 12-13z.

DMX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 9 PM CDT Tuesday for IAZ004-005-015- 023>025-033>037-044>050-057>062-070>075-081>086-092>097. Extreme Heat Warning from noon Monday to 9 PM CDT Tuesday for IAZ006-007-016-017-026>028-038-039.