574 FXUS63 KDMX 100444 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1144 PM CDT Mon Aug 9 2021 .DISCUSSION.../Tonight through Monday/ Issued at 212 PM CDT Mon Aug 9 2021 At 19z GOES satellite imagery shows an upper low swirling just east of the local area, centered near the WI/IL border. Stratus has been stubborn to dissipate on the northwestern periphery of the low which has hampered temperatures a bit over northern Iowa so far today. For the most part the passing low featured little baroclinic component as conditions remain warm and humid in its wake. Temperatures in the 80s to low 90s with dewpoints in the low to mid 70s are common, pushing heat index values to near or above 100 degrees in some locations. A broad mid-level trough axis swings into the northern Plains tonight. Models develop showers and storms just north of the area along a surging frontal boundary. It is possible that a convective complex builds south into deeper instability and clip our northern counties toward the morning hours, but kept PoPs low since the preferred storm track still looks mostly north and east of the forecast area. Frontal boundary stalls out over the state on Tuesday. Conditions will once again be hot and humid especially to the south of the boundary where a heat advisory was issued. Expect peak heat index values of 105+ within the advisory area including the DSM metro. Thunderstorm chances begin to nudge up by late in the day as the atmosphere becomes increasingly unstable characterized by SBCAPE in excess of 4000 J/kg. Kinematic forcing associated with the mid- level wave is rather nebulous, and low-level frontal convergence is meager at best. Thus a weak cap may be sufficient to keep a lid on any convective development for much of the day. Most model solutions initiate convection as the LLJ ramps up after 03z, but the location of CI is highly variable ranging anywhere from northwest MO to northeast IA. Large hail and strong wind gusts will be a concern with any convective activity as the atmosphere remains highly unstable into the overnight hours, although rooted mostly above 800mb or so. Deep layer shear is more modest ~20-25 kts as the core of faster flow aloft remains off to the north. The surface boundary washes out on Wednesday and provides little to no baroclinic contribution, and thus not expecting much in the way of widespread heat and humidity relief. Instead it will likely be another day of hot and humid conditions and potentially more heat headlines central and south. More comfortable conditions hold off until late week as a surface high drops south out of Canada. This will scour out the thick humidity and bring highs back into the low to mid 80s. A few storms are possible late Thursday into Friday across the south as a weak boundary moves through. Long range models begin to significantly diverge over the weekend with the GFS being more progressive to push the surface high eastward and bring humid, southerly flow and precip chances back into the state by Sunday. The Euro is much slower and keeps the surface high and drier air around through the weekend. Ensemble guidance is also somewhat split at that range, so the dry NBM forecast is appropriate for now. && .AVIATION.../For the 06Z TAFS through 06Z Tuesday night/ Issued at 1141 PM CDT Mon Aug 9 2021 While there is some threat for thunderstorms during the period, placement and timing remain uncertain, therefore are not mentioned in the TAFs. Ceilings and visibilities to remain mostly VFR although some patchy fog toward daybreak on Tuesday morning may produce some MVFR vsbys. Surface winds generally south to southwest for much of the time. && .DMX WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon to 7 PM CDT Tuesday for IAZ027-028- 037>039-047>050-058>062. Heat Advisory until 7 PM CDT Tuesday for IAZ070>075-081>086- 092>097. && $$ DISCUSSION...Martin AVIATION...Cogil