838 FXUS63 KDMX 100702 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 202 AM CDT Tue Jun 10 2025 .KEY MESSAGES... - Areas of smoke to persist tonight - Noticeably warmer Wednesday - Next chance (60-70 percent) for more organized, widespread precipitation Wednesday afternoon, Wednesday night & into Thursday && .UPDATE... Issued at 202 AM CDT Tue Jun 10 2025 No substantive changes to the forecast through Wednesday morning, with quiet and increasingly mild conditions during that time. All eyes are on thunderstorm and severe weather chances from Wednesday afternoon onward as we enter a considerably more active weather period. The overall set-up will be typical for the season, with a warm/stationary surface front underlying moderate zonal flow aloft, instability pooling south of the boundary, interactions with mid-level shortwave impulses and/or the nocturnal low-level jet providing forcing mechanisms for convection, and the resulting storms influencing the location of the front and degree of instability in subsequent rounds of potential initiation. In such situations, predictability is normally highest with the initial round and decreases incrementally thereafter. For tonight`s update have only focused on the first round of storms late Wednesday. By midday Wednesday the surface warm/stationary front will be draped from west-to-east across northern Iowa, likely somewhere between Highway 30 and Highway 18. To the south of the boundary, southwesterly surface flow and relatively deep mixing will induce temperatures to climb to their highest levels of the year so far, with highs in the lower 90s and dewpoints in the mid-60s. This will feel sweltering given our recent persistent spate of cooler than normal weather. It will also cause instability to pool against the front, with MUCAPEs in the 2000-3000 J/kg range by mid-afternoon. A mid-level impulse approaching from South Dakota will arrive coincident with peak heating/destabilization and initiate strong convection somewhere over northwestern/northern Iowa in the mid-to-late afternoon, with a cluster of storms moving eastward along the front and perhaps southeastward into the pool of instability. Farther south, toward central and even southern Iowa, some new CAM runs are generating storms and soundings do show an uncapped and very unstable airmass, however there appears to be no forcing/focus mechanism for such storms and have kept POPs low in those areas. In terms of a severe weather threat, certainly instability will be more than sufficient, at least along and south of the front. However, shear will be modest with 0-6 km Bulk Shear values around 30-35 KT along the boundary, and less to the south. 0-1 km is even less impressive, with relatively light and unidirectional near-surface flow resulting in values of only 5-10 KT. In this scenario, the most likely mode for severe weather will be large hail, though there is some potential for strong winds as well given the large CAPE profiles, especially if an organized group of storms can establish a cold pool and become forward-propagating. In addition to severe thunderstorm threats, heavy rain is also a distinct possibility, especially heating into the overnight Wednesday night as additional thunderstorms may fire north of the boundary and train over the same areas to some extent. However, with less forcing for ascent overnight it appears QPF may not be as robust as it looked like it could be a couple nights ago, and in addition our northern counties have good capacity given the antecedent conditions. Still, it is certainly a threat worth monitoring and we will be watching the Wednesday afternoon-night timeframe closely as it approaches. && .DISCUSSION... Issued at 232 PM CDT Sun Jun 8 2025 Main forecast concern today centers on the mid to late week system. Upper low is finally departing across the Great Lakes, with the pattern adjusting to a more zonal flow over the midwest. As the surface ridge slides off to the south and east Tuesday, a warm front sets up in its wake over northern Iowa. This front will provide the initial focus for storms Wednesday. Given the available instability near and especially south of the boundary, thunderstorms are likely. Given the instability, could see some embedded severe storms as well. The front is expected to linger in the vicinity of northern Iowa/southern Minnesota through Thursday, keeping the rain chances around through the period. The details for Thursday depend largely on the position of the front and any remnant outflow boundaries from convection the day/night before. Given the zonal flow aloft along the boundary and available moisture, areas near the front and aforementioned boundaries will need careful monitoring for heavy rain and flooding potential. Meanwhile, energy currently over southern California is forecast to meander across the southern US and potentially interact with the northern stream by late week. Lots of spread in the model solutions however, so confidence remains low at this time on this evolution. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1045 PM CDT Mon Jun 9 2025 VFR conditions are expected through the period with little cloud cover expected. Wildfire smoke will be passing across Iowa again but at this time no impacts to vsbys is forecast. Light west wind overnight may become breezy at times on Tuesday before diminishing and turning more southerly in the evening. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Lee DISCUSSION...DMD AVIATION...Donavon