297 FXUS63 KLSX 111856 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 156 PM CDT Wed Jun 11 2025 .KEY MESSAGES... - Warm, pleasant weather continues through Thursday with the St. Louis and Columbia metro areas potentially reaching 90 degrees for the first time this year. - Increased humidity marks the return of showers and a few weak thunderstorms late Thursday that persist through early next week. && .SHORT TERM... (Through Late Thursday Night) Issued at 136 PM CDT Wed Jun 11 2025 Water vapor imagery reveals a broad trough centered over Texas, largely detached from the subtropical jet over the northern CONUS and southern Canada. Given the upper troughs distance from the jet stream, it will only slowly meander to the northeast and will be the focus of the forecast for the next several days. Today, the clearest evidence of that trough approaching the Mid Mississippi Valley is the shift to southwesterly winds throughout most of the troposphere. These southerly winds are advecting warmer air into the region, but are also pulling in deeper moisture and slightly greater cloud coverage. As of 2pm, temperatures had climbed into the mid to upper 80s in many areas across the CWA, so we`ll still make a run at 90 degrees in many locations, but the increasing thin clouds may keep many locations just shy of that mark. The upper trough will continue to inch closer to the CWA tonight and tomorrow, drawing even more moisture into the area. This will further bolster cloud coverage and thickness, and should keep temperatures from dropping off too much tonight and a bit of a lid on temperatures tomorrow. In fact, even the 90th percentile of the NBM maximum temperature is below 90 degrees for the vast majority of the forecast area tomorrow. The deeper moisture, combined with limited forcing on the northeast periphery of the upper low, will also bring the first chances for rain associated with this system into the region. Most CAMs have at least a few showers moving across portions of central and NE MO late tomorrow morning and into the afternoon, but coverage is expected to be limited due weak forcing. BSH && .LONG TERM... (Friday through Next Wednesday) Issued at 136 PM CDT Wed Jun 11 2025 By Friday, the upper low will have finally made it to Missouri, resulting somewhat more robust forcing and even richer moisture across the Mid Mississippi Valley. In fact, both ECMWF and NAEFS ensembles push precipitable water to right around the 90th climatological percentile by Friday afternoon. This deep moisture, coupled with the transient-but-modest forcing across the region, will almost certainly bring showers and a few thunderstorms to the area, especially across our south. That said, given the limited forcing, showers and thunderstorms will be more scattered in coverage, and this limited coverage is what`s keeping our precipitation chances limited to about 80%. The modest forcing will also limit thunderstorm organization and strength, meaning that chances for severe thunderstorms are rather low (< 5%). With slow storm motion and anomalously high moisture, I can`t rule out locally heavy rainfall, but even those chances are on the low end (< 10%) as well. The upper trough will slowly depart the region on Saturday, and several of the deterministic models have begun depicting a reinforcing shortwave dropping south into the area on Sunday afternoon/evening. These features will interact with the lingering moisture, keeping the chance for showers and thunderstorms in the region through the weekend, with the highest chances in the afternoon and early evening. We`ll be at least partly cloudy on both days as well, limiting temperatures to the low to mid 80s. As we move into next week, the upper level pattern becomes a bit more zonal, with most models showing a series of weak shortwaves pushing through the region. This will keep rain chances in the forecast through at least the first part of next week along with seasonal temperatures. BSH && .AVIATION... (For the 18z TAFs through 18z Thursday Afternoon) Issued at 1208 PM CDT Wed Jun 11 2025 Yet another quiet set of TAFs as we await a meandering low pressure system currently over TX. While that system approaches the area, we`ve seen winds turn more southerly and are beginning to see an uptick in upper level clouds. This will persist through the TAF period, with clouds further filling in an lowering. These clouds should keep temperatures warmer tonight than the last few nights, so fog appears less likely. A chance of precipitation moves into the area late tomorrow morning, but precip chances are too low at this point to include in the TAFs. BSH && .CLIMATE... Issued at 525 AM CDT Wed Jun 11 2025 As of this writing, 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, and this is 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/MRB && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX