167 FXUS63 KDMX 291957 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 257 PM CDT Mon Jun 29 2026 .KEY MESSAGES... - A prolonged period of hot and humid conditions will continue through the coming week and potentially the Fourth of July weekend. An Extreme Heat Warning is in effect for the entire area. - Severe thunderstorms are possible this evening into the overnight in northwest Iowa, with damaging winds being the primary threat. However, there is uncertainty in how far into our warning area these storms may advance. && .SHORT TERM /THROUGH TUESDAY/... Issued at 256 PM CDT Mon Jun 29 2026 The heat wave is in full swing across the state today as heat indices are already topping 100F this afternoon and may continue to climb a few degrees further, while perhaps being just a couple degrees behind schedule with the presence of cumulus possibly limiting sunshine. Dewpoints are well into the mid 70s and may continue reaching towards the upper 70s through the rest of the afternoon and evening. Immense amounts of instability is being built beneath a stout cap, now over 6000 J/kg in a large part of the state. Remarkably strong synoptic winds for this time of year are being mixed down from 850 mb, caused by the low to our north, causing wind gusts on the order of 30 knots across a good part of the state. As we head into the evening, a slight risk is in place across our far northwest, with multiple chances at storms tonight. 700mb temps will be 15C across most of the state this evening, keeping us clear of any storm chances, but towards 03z the cold front approaches our far NW counties, and 700 mb temps cool in a narrow zone ahead of the cold front. CAMs are split about 70/30 in favor of storms briefly trying to form early evening and eventually being capped off before making it into our CWA. However, some solutions have convection robust enough to build up a cold pool that continues into a few counties of our area and trudges through that very unstable and very capped airmass sitting across the warm sector. These storms would pose mainly a damaging wind threat by the time they get to our CWA, but large hail and even a tornado is possible if a storm complex can take advantage of the strong 0-1km shear. Assuming a large cold pool doesn't develop during the mid evening and exhaust the environment, another shot at severe storms across our NW will happen towards 7-9z. The nocturnal LLJ surges with a new shortwave over the central plains tonight. Elevated convection will likely develop at the nose of the LLJ and in the post frontal zone of the slowing cold front over central Nebraska near 4-6z. As the front reorients tonight, this elevated convection will try to ride the theta-e gradient from central NE to far NW IA. As it does, it's cold pool may attempt to nudge further into the highly unstable airmass across our NW CWA. The uncertainty lies in how effective this cold pool can be at lifting capped parcels to their LFC to take advantage of the instability. Given strong capping, and mediocre mid level shear, but strong instability, the most likely solution is the overnight MCS with some damaging wind potential impacts far northwest IA, perhaps including a couple of our counties, but is unable to advance further southeast away from the frontal boundary. On Tuesday, a similar pattern is in place, with ridging to the southeast, ample sunshine, and mid-70s dewpoints causing extreme heat. Headlines last through all of Tuesday to account for yet another day of 100+ degree heat indices and lack of any relief from limited cooling overnight. Overnight cold pools may perhaps keep temps a tick lower across NW Iowa on Tuesday, but there is still high confidence in extreme heat across the rest of the state. Renewed chances for storms exist again in the evening and overnight Tuesday as the nocturnal LLJ surges again to the west and perhaps initiates storms that run across the theta-e gradient once again. However, storms are possible earlier in the evening for central and northern Iowa as CAMs are hinting at some convection along the wind shift boundary as we reach peak instability. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Issued at 256 PM CDT Mon Jun 29 2026 A similar pattern remains in place through Saturday. High pressure to our southeast will keep the heat and humidity in place, especially across the central and southeast part of the state. Heat indices may drop a tad, but the danger may lie more in the continued days of heat, and the lack of overnight relief with lows in the upper 70s. Therefore, the extreme heat warning has been extended for a large part of the state through at least Wednesday with anticipation of possible further extension in the coming days. As has been talked about the last few days, the heat is expected to continue through the 4th of July weekend, where heat indices on the order of 100 are still being forecast. Storm chances will continue each day, particularly in the western and northern part of the state, as the ring of fire pattern continues. The usual pattern will continue to be large instability built up during the day, LLJ surges at night, and initiates storms overnight that attempt to push east through the highly capped environment over our CWA. Though marginal, it is also worth mentioning the excessive rainfall outlooks across Iowa. With large PWAT and storm chances, chances for flash flooding can't be ruled out on any given day. Per the usual for this time of year, these storm chances will be highly uncertain in their exact timing and intensity. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1247 PM CDT Mon Jun 29 2026 Scattered to broken cumulus across the terminals are causing occasional MVFR conditions this afternoon, particularly at KMCW, but all sites should maintain VFR conditions by mid afternoon through the end of the TAF period. Confidence is high in LLWS at all sites beginning late evening through the overnight as surface winds begin to calm, though there is a chance LLWS begins earlier than what is included in this issuance. Additionally, there is a low (~20%) chance for thunderstorms at KFOD and KMCW through the evening/overnight but confidence is too low to include in this issuance. && .DMX WATCHES/WARNINGS/ADVISORIES... Extreme Heat Warning until 9 PM CDT Tuesday for IAZ004>007- 015>017-023>028-033>039-044>050-057>062-070>075-081>086- 092>097. && $$ SHORT TERM...De Bruin LONG TERM...De Bruin AVIATION...De Bruin