textproduct: Des Moines

KEY MESSAGES

- A prolonged period of hot, muggy, oppressive weather will begin Sunday and is likely to continue in large part through the coming week and potentially the Fourth of July weekend. An Extreme Heat Watch has been issued from Sunday afternoon through Tuesday evening.

- Before the heat sets in on Sunday, widely scattered showers and isolated thunderstorms are expected tonight into Sunday morning. A few storms may be strong and produce hail or gusty winds, but the overall severe weather threat is low.

- The heat wave may be disrupted briefly by overnight thunderstorm chances some days next week, especially in western and northern Iowa. Locations and which nights may offer the best storm chances will be refined over the coming days.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 219 AM CDT Sat Jun 27 2026

A large 500 MB gyre is sliding down the British Columbia coast early this morning, while a latitudinally stretched ridge lies across the far southern U.S. near the Gulf coast. Weak ridging extends northward across the central U.S. and in advance of the aforementioned gyre, and will promote generally quiet and a bit warmer weather today. At the surface, a large high pressure area remains stubbornly anchored over the Great Lakes region, while a broad low pressure trough is gradually developing along the lee of the Rockies. A large pool of saturated near-surface air is stuck across portions of the Midwest, manifesting as a large blanket of very low clouds and spotty light fog that currently covers most of Missouri, about the southern two thirds of Iowa, and parts of neighboring states and is advecting slowly northward at the current time. Radar imagery occasionally depicts a few faint echoes within the cloud field, but an apparent lack of forcing has prohibited any rain overnight, and will maintain a dry forecast through the morning hours.

During the day today the High Plains surface trough will gradually expand, and while the Great lakes high attempts to maintain its position, the tight pressure gradient between the two systems will be pushed eastward toward Iowa and result in modestly increasing southeasterly breezes and weak but persistent warm air and moisture advection. The thick low clouds will likely persist through much of the morning, but this afternoon diurnal mixing should be sufficient to at least somewhat break these clouds up, allowing temperatures to rise a bit further than the previous few days with highs in the lower 80s or so. Meanwhile, a 500 mb shortwave impulse currently near the Oklahoma panhandle will drift east northeastward across Kansas and Missouri today, generating some showers and thunderstorms in that region this afternoon and evening. The impulse will be fading a bit by the time it reaches northern Missouri late today, and any showers and storms may also encounter somewhat more stable air depending on the degree of clearing that occurs. Meanwhile, a complex of stronger storms will develop over South Dakota tonight but move northeast or east northeast into Minnesota and largely miss Iowa. There is some potential that outflow south of this complex may trigger showers and thunderstorms in northern Iowa late tonight into Sunday morning. While warm/theta-e advection and MUCAPE values appear to support some potential for strong updrafts overnight, forecast soundings illustrate relatively weak speed shear in the elevated layer above a fairly deep near-surface stable layer. Overall, any storms that reach our area tonight into Sunday morning should be spotty and generally benign, though there may be a brief window of opportunity for some gusty winds near the Missouri border early tonight as the fading impulse moves by just to our south/southeast and before the near-surface stable layer deepens overnight.

By Sunday the High Plains low pressure trough will be deeper, broader, and finally push the pressure gradient eastward and kick the Great Lakes ridge away. This will bring low-level flow around to southerly across Iowa even as 500 MB flow becomes increasingly southeasterly ahead of the approaching Pacific Northwest gyre. In this scenario Gulf moisture will stream northward and temperatures will warm significantly. By Sunday afternoon any lingering morning showers/storms will be gone, skies will be clearing, and temperatures will peak in the low to mid-90s with dewpoints climbing into the 70s. This will result in Heat Index values peaking around 101-106 across much of our forecast area, marking the first day of true summer heat and humidity experienced so far this season. If anyone has weekend plans and wants to avoid the hot and muggy conditions expected on Sunday, they would be well advised to complete them today if possible! Persistent southerly flow Sunday night will keep temperatures from falling much, with hot and muggy conditions persisting as lows will only be in the mid to upper 70s Monday morning. Excessive heat will continue for much of the coming week, as discussed further in the Long Term section below, and prompting the issuance of an Extreme Heat Watch beginning early Sunday afternoon.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 219 AM CDT Sat Jun 27 2026

By Monday morning the 500 MB gyre currently sliding down the British Columbia coast will have carved out a deep trough across the western U.S. As it does so, the elongated 500 MB ridge currently squashed in the far southern U.S. will pivot up into the southeastern states and intensify in response, setting up a blocking pattern that will persist for much of next week. The western U.S. trough will be reinforced by, and wobble around due to the injection of, additional vorticity nuggets from the eastern Pacific. Meanwhile, the southeastern U.S. heat dome will reach its maximum overall intensity and proximity to Iowa on Monday and Tuesday. Between these two systems, southwesterly 500 MB flow will provide ample moisture and instability for a proverbial "ring of fire" scenario in which several rounds of thunderstorms are likely to develop and advect northeastward around the periphery of the heat dome. The location of the resulting swath/s of storms remains uncertain and is likely to shift around a bit from day to day. Most long-range solutions the past few days have kept the bulk of these storms northwest of our area over the High Plains and Upper Midwest, however, there is certainly some possibility for our area to be impacted at times with the highest potential in our northwestern counties. Barring any convective effects, however, a prolonged period of very hot and humid conditions is expected with multiple days of Heat Index values exceeding 100 degrees across much of the area. This has prompted the issuance of an Extreme Heat Watch from Sunday afternoon through Tuesday evening. While on any given day Heat Index values may remain below 110 degrees, the number of consecutive days with values peaking roughly around 105 degrees, as well as persistent overnight lows in the mid/upper 70s and the fact that this is the first true summer heat of the year and comes during a holiday week with many outdoor activities planned, may prompt an upgrade of part of the watch to a warning later today, and eventually an extension past Tuesday evening.

From Wednesday onward the confidence in forecast details and especially thunderstorm potential gradually decreases, however, the synoptic pattern will essentially remain in place. In fact, there are increasing signs from long-range model solutions that the western U.S. trough will largely shift northward into Canada by the end of next week, allowing the heat dome to expand across much of the central U.S. although it may also become a bit more diffuse as a result. Nevertheless, to one degree or another the summer heat that begins on Sunday will likely continue right on through the following Fourth of July weekend and perhaps beyond.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1046 PM CDT Fri Jun 26 2026

MVFR to IFR cloud cover continues to leak northward into southern Iowa this evening and will do so through the morning. Patchy fog is also resulting in low visibilities over southern Iowa, which may push slightly farther north toward KOTM so have included a tempo through the morning to account for this. Clouds are expected to improve some as mixing occurs on Saturday, but occasional MVFR conditions may persist at times through the day. Winds remain light out of the east tonight, then increase out of the southeast through the day.

DMX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Watch from Sunday afternoon through Tuesday evening for IAZ004>007-015>017-023>028-033>039-044>050-057>062- 070>075-081>086-092>097.