824 FXUS63 KLSX 090232 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 932 PM CDT Tue Jul 8 2025 .KEY MESSAGES... - Scattered thunderstorms are expected to track southeast through the region today. A few thunderstorms could be strong, including the potential for isolated severe thunderstorms with winds gusts to 60 mph and locally heavy rain. - Warm, seasonable temperatures will persist through the next several days along with periodic chances for thunderstorms to impact the region. && .SHORT TERM... (Through Late Wednesday Night) Issued at 138 PM CDT Tue Jul 8 2025 Thunderstorm potential will be the primary focus this afternoon into this evening as an upper level trough and MCV (mesoscale convective vortex) rotate southeastward through late this evening. IR satellite shows a broad expanse of broken/overcast clouds extending from northern MO through portions of IA/IL/WI. Clouds are associated with the MCV, remnant of a convective complex that developed over SD/NE last evening. Another area of clouds and convection extend from eastern OK into southern IN. In between the two areas, skies have remained mostly clear, allowing instability to build ahead of the approaching MCV. As of 18z, SPC mesoanalysis shows a what little CIN that exists extending from Kansas City roughly just west of Quincy, IL. Where skies have remained mostly clear, surface instability has climbed with 2500 J/kg of SBCAPE roughly along and north of the I-44 corridor into southwestern IL along I-70. This not only jives pretty well with guidance from prior runs, including this morning, and maybe even on the higher end. HREF means showed SBCAPE of 2-2.2k with deterministic hi-rese guidance (RAP/HRRR) plotting 2.5-3k this afternoon. Moisture is no question with dewpoints in the upper 60s to low-70s and PWATs around 1.7" per SPC mesoanalysis. Thunderstorms will certainly have the moisture to produce efficient rainfall with locally heavy rain, resulting in ponding/nuisance flood in areas impacted by multiple cells. Though soundings aren`t showing a particularly classic inverted-V, 50-100mb dewpoint depressions in the realm of 10-13C suggest localized downbursts with marginally severe wind gusts (60 mph) are possible. Hail cannot be entirely ruled out, but what does fall is likely sub-severe with mid-level lapse rates at 5.5-6C and competing updrafts as scattered convection become more numerous in time. Despite some slight spatial/temporal variability between deterministic hi-res models, paintball plots (simulated reflectivity >40 dBZ) show a general consensus that the best timeframe for development runs from near KCOU to just south of KPPQ. IR satellite is showing a notable uptick in development in this region, increasing confidence that this will be the region for focused initiation. Thunderstorms then move southeast through approximately 8-9 p.m. as thunderstorms progress southeast and weaken after sunset. Once thunderstorms clear to the southeast and dissipate late this evening, clouds likely hang on for some time tonight before partial clearing works into northeast MO. There is some hint at patchy fog development running from central to northeast MO, but cloud cover may not clear quick enough before sunrise, limiting fog potential. This will be something to monitor through tonight, but even if fog develops, it is not expected to be anything significant with the limited time to take advantage of clearing. By Wednesday, mostly dry conditions are expected with the low chance that an isolated shower may develop. However, much of the potential will reside outside the CWA. Should anything develop, the best chance (30-40%) will line up along the southeast portion of the CWA with chances quickly tapering to the north and dropping through the day as surface high pressure builds in from the northwest. Maples && .LONG TERM... (Thursday through Next Tuesday) Issued at 248 PM CDT Tue Jul 8 2025 Ensembles and NBM guidance show a persistent, seasonably warm pattern with relatively small spread through the extended range. Variability is greatest on days with better convective potential and even then, spread is considerably small in comparison to events involving wholesale change. The upper level ridge centered over the Desert Southwest is expected to flatten and shift westward over southern CA and the Baja Peninsula by Thursday. This results in southward shift in the active 500mb vort track that has kept the northern CONUS active over the last several days. Several shortwaves continue to round the northern periphery of the ridge, progressing west to east over the Intermountain West into the central Plains and mid- Mississippi Valley. Though this looks like an opportunity for multiple, periodic rounds of convective potential, surface features and timing will be key in the magnitude and spread of activity. Surface high pressure moves into the Great Lakes but maintains some influence early Thursday as the first such shortwave tracks near the IA/MO border. This looks pretty close to scenarios we`ve seen pan out over the last couple of days with afternoon/evening convection initializing to the north and tracking southeastward at the eastern periphery of the upper ridge. However, this round forms at the nose of a 40-45 knot low level jet that set up over the central Plains. Deterministic guidance (ECM/GFS) is fairly good agreement with the placement of this system at this time, which would have convective trends moving somewhere along the MS River Valley into MO/IL Thursday morning. Usually convective complexes of this nature will weaken as the low level jet fades through the day and the complex become outflow dominant. Nonetheless, it may be something to watch should timing/placement shift over the next couple of days. Chances for showers and thunderstorms are most favored over northeastern MO and west- central IL in this scenario, as convection would tend to weaken through the morning/early afternoon (if it lasts that long). Friday largely looks dry as we await the next uptick in thunderstorm potential, which may be the best shot over the course of the week. This will come in the form of a deeper trough that closely follows Thursday`s lead shortwave. This shortwave give rise take on a slight negative tilt ahead of an amplified, positively tilted trough that extends southwestward into the northern Plains. As the shortwave approached, the surface low is ejected northeast through the central Plains into the Upper Midwest. A cold front that trails the system slow pushes southeast late Friday into early Saturday. While this may be the best opportunity for rainfall provided surface convergence underneath mid/upper ascent, where the system track and when it moves through will play a huge role in precipitation potential. If the upper trough and shortwave track too far north, this would place the mid- Mississippi River Valley in territory in which the cold front relies on diurnal instability and convergence. While diurnal convection would result in beneficial rainfall, thunderstorms potential would struggle to survive through the diurnal lull. Therefore, while there are multiple opportunities for rainfall, there are enough caveats to questions just how much of it will come to fruition to benefit the region with widespread potential. Maples && .AVIATION... (For the 06z TAFs through 06z Wednesday Night) Issued at 932 PM CDT Tue Jul 8 2025 The main concern for overnight is fog potential. Continue to think that the best chances are in central Missouri as both KCOU/KJEF did receive some rain and at least some partial clearing is likely overnight. IFR visibilities are expected at both of these terminals late tonight into early Wednesday morning. Elsewhere, the fog potential is a lower due to lingering cloud cover. KSUS may at least have a brief period of MVFR visibilites as some late partial clearing is expected before daybreak. Any fog should quickly lift/dissipate by 1300 UTC, with dry/VFR conditions and light/variable winds expected through Wednesday evening. Cannot completely rule out a rogue shower/weak thunderstorm on Wednesday afternoon, but the coverage continues to look much too low to add any VC or PROB30 mention to any of the terminals at this juncture. Gosselin && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX