218 FXUS63 KLSX 072353 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 653 PM CDT Sat Jun 7 2025 .KEY MESSAGES... - Thunderstorms moving into the region this afternoon will pose an isolated damaging wind threat and low tornado threat through early this evening across central and southeastern Missouri. - Another round of thunderstorms is expected along a cold front tomorrow afternoon and evening. A few storms will become strong to severe, with the main threats being damaging wind gusts and large hail. - Relatively calm weather is expected Monday through Wednesday before an active pattern returns at the end of the week into the weekend. && .SHORT TERM... (Through Late Sunday Night) Issued at 206 PM CDT Sat Jun 7 2025 Water vapor imagery this afternoon shows a compact shortwave moving into the Lower Missouri Valley, with its surface reflection moving into central Missouri. The early morning convective complex that tracked through the Mid-South produced a blanket of mid to upper- level cloud cover over the CWA ahead of the shortwave, which when combined with low stratus from the earlier fog, has limited surface heating over much of the area. A brief bout of warm air advection via southwesterly low to mid level flow ahead of the wave will offset the effect of this cloud cover to some degree over portions of central and southeastern Missouri. Here, an area of 1,000-1,500 J/kg of MLCAPE is nosing into central Missouri among about 50 kts of effective shear. These attributes are favorable for strong to severe storms, though the CAPE profile is tall and thin, with soundings showing a weak inversion at about 500 mb. This may keep updrafts shallow and limit their ability to fully recognize the amount of shear in place. That being said, this system resembles an MCV, and these are notorious for overperforming relative to the environment they are in. As line segments associated with this system move through west-northwestern Missouri, weak mesovortices have been noted along the leading edge. Shear in the 0-3km layer is weaker - about 20 kts - which is not favorable for robust mesovortex development. However, SPC mesoanalysis shows that the shear increases with southern extent, and any east-northeastward oriented segments will be able to utilize for mesovortex development, posing an isolated damaging wind and low tornado threat. This threat will extend from central Missouri southeastward in time through southeastern Missouri into the early evening. With abundant low level moisture, weak winds, and some clearing, another round of fog, possibly dense, is expected tonight. The most favorable area for this is across central Missouri thanks to more clearing forecast there. Other portions of the area further eastward may also experience fog, though how dense remains uncertain. Through Sunday, the shortwave will depart the region to the east- northeast as a deep upper-level trough begins to dig into the Northern Plains and Midwest. This trough will send a cold front surging south-southeastward through the Midwest through the day, entering the CWA sometime during the afternoon. Mostly clear skies ahead of the front will allow for surface heating and MLCAPE to around 1,500 J/kg among about 30 kts of 0-6 km shear. Convergence along the front will be weak, though enough to pair with falling heights to produce isolated to scattered convection. Given the shear profile, a multicellular storm mode with transient supercellular structures are favored. Updrafts will be tall, favoring enough CAPE in the hail growth zone to lead to a large hail threat initially, and high LCLs/inverted V soundings support a damaging wind threat. Deep-layer shear vectors becoming increasingly parallel to the advancing front will favor updrafts to be undercut and possibly congeal with time, favoring a transition to mainly a damaging wind threat. Given convection likely being undercut with time and uncertainty in frontal timing, how far southward the threat for storms extends into the CWA is uncertain. Current indications are that a corridor from central Missouri northeastward into west- central Illinois is the most favorable to see storms capable of isolated to scattered severe threats. Some deterministic soundings show a warm nose/capping through most of the day, so there is a low chance that convection could struggle to form altogether. High LCLs are expected to mitigate a tornado threat. Elmore && .LONG TERM... (Monday through Next Saturday) Issued at 206 PM CDT Sat Jun 7 2025 To start the workweek, guidance is unanimous in an anomalously deep trough digging equatorward over the central CONUS. This trough will send yet another cold front through the CWA sometime during the day on Monday. Given the previous FROPA resulting in minimal moisture over the CWA and weak convergence along the front, confidence is high (90%) in a dry FROPA. In the wake of the front, deep northwesterly flow will keep our weather quiet and temperatures just on the cool side of climatological normals, with ensembles tightly clustered around 80 degrees for highs through Tuesday. Our weather stays calm through Wednesday, though temperatures will begin warming then as the upper-level trough shift east, allowing ridging to build into the region, supporting southwesterly mid-level flow and warmer 850 mb temperatures. Toward the end of the week into the weekend, guidance depicts a series of shortwaves/cutoffs moving beneath the ridge and/or along its eastern periphery impacting the Middle Mississippi Valley. This regime will return active weather to the region, with periods of showers and thunderstorms forecast Thursday through Saturday. There will likely be plenty of dry time within this stretch, but guidance variability in the phasing of the shortwaves and thusly, rain chances, causes blended guidance such as the NBM (our forecast) to have a broad smattering of low to medium precipitation chances over a prolonged period of time. The warming temperatures and increasing moisture over the area will build instability, but guidance consensus is that deep layer shear will remain meager beneath the ridge, mitigating a more notable severe thunderstorm threat as of now. Elmore && .AVIATION... (For the 00z TAFs through 00z Sunday Evening) Issued at 644 PM CDT Sat Jun 7 2025 Light showers are expected to linger around STL/SUS/CPS through 02Z. Then expect stratus with ceilings between 1500-2500ft AGL at COU through 02Z and STL/SUS/CPS through 14Z. There will also be fog lingering through the night with IFR/MVFR visibilites at UIN/COU/JEF/SUS. Visibilities will improve on Sunday morning, but there will be a chance (30-40%) of thunderstorms at UIN/COU/JEF after 18Z and at STL after 00Z. Britt && .CLIMATE... Issued at 227 PM CDT Fri Jun 6 2025 St Louis has still not seen 90 degrees yet in 2025. The average first 90 degree reading is May 20. The most recent late 90-degree start was June 10, 2021. If St Louis doesn`t hit 90 by June 10, it will be the latest first 90 degree day since at least 1995 (June 19). The latest date of first 90 degrees on record was July 4 in both 1961 and 1912. Columbia has also not yet seen a 90 degree reading in 2025, however the average first date is much later (May 31). The latest date of first 90 degrees on record was July 14, 1904. Quincy reached 90 degrees on May 15 of this year, about 3 weeks earlier than their average first 90 degrees (June 2). Kimble && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX