604 FXUS63 KLSX 121125 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 625 AM CDT Thu Jun 12 2025 .KEY MESSAGES... - Increased humidity marks the return of showers and a few thunderstorms later today that persist through the middle of next week. Even in southeast Missouri and southwest Illinois, where rain chances are highest, the weekend won`t be a washout. - After a dip in temperatures this weekend, more seasonable warmth returns next week. && .SHORT TERM... (Through Late Friday Afternoon) Issued at 339 AM CDT Thu Jun 12 2025 A shield of cirrus clouds continue to stream north into the Mid- Mississippi Valley per the latest GOES-East Nighttime Microphysics output, riding weak but persistent moisture transport and isentropic ascent from the Gulf. Aloft, a sluggish cutoff wave is evident on GOES-East Mid-Level Water Vapor imagery meandering north and east from the southern Plains. Along its leading edge, the southerly flow is further promoting weak moisture and warm air advection poleward. Cloud cover will only increase through the day today, sufficiently stunting insolation and keeping temperatures a few degrees cooler than yesterday. High-resolution guidance is keying in on a local minimum in low-level moisture lee of the Ozarks across east-central Missouri into parts of southwest Illinois today. Along with limited surface heating today, that will severely hamper instability (and convection) across most of the region. The highest HREF/REFS probabilities of at least 500J/kg of SBCAPE are consistently across northeast Missouri and west-central Illinois, where the highest PoPs generally are today. Elsewhere, while the southwest flow aloft may help stimulate a few weak showers, expect plenty of dry time. Moisture advection continues through the night as the trough approaches the bi-state, establishing precipitable water values near the 90th climatological percentile areawide by Friday. Model soundings continue to depict a favorable thermodynamic environment for localized downpours, but the kinematics surrounding this system remain unimpressive to support stronger convection or a more tangible heavy rain threat. The best threat for locally-heavy rain tomorrow will exist coincident with a corridor of stronger integrated water vapor transport in far southeast Missouri and southwest Illinois, where LPMM output suggests up to 1.50" may fall locally by late Friday night. Further north and west of here, while heavy rain won`t be too much of a threat, a weak surface low may form to stimulate more stratiform rain or weak showers during the day. I doubt Friday will be a washout, but the chances for more widespread rain are certainly higher than today. MRB && .LONG TERM... (Friday Night through Wednesday) Issued at 339 AM CDT Thu Jun 12 2025 Upper-level low and its surface reflection will still influence our sensible weather to start the weekend. Save for areas in northeast Missouri, isolated to scattered showers and a few thunderstorms will result primarily in the afternoon coincident with the diurnal instability peak. The best chances for rain are once again in our southeast Missouri and southwest Illinois counties where the "best" mid-level ascent will reside. That said, the system will be exiting through the afternoon to the east, and most will see more dry time than rain with temperatures in the mid-80s. Sadly, it`ll be one of the muggier days of the year so far with dewpoints jumping into the low 70s. Most of the ensemble envelope and deterministic guidance concur that Sunday will be largely dry with the surface low departing and heights rising aloft. However, by this point another shortwave takes aim at the region to threaten additional scattered showers and a few thunderstorms to start the next work week. This feature will not be working with as noteworthy moisture as the wave over the weekend, which will generally limit convective intensity and coverage. This starts daily chances for scattered showers and thunderstorms, with the chances peaking in the afternoon along with the diurnal instability maxima. Deep-layer shear stays largely unimpressive with the subtropical jet relegated to the northern CONUS, keeping the threat for stronger thunderstorms very low (5-10%). Temperatures will be on the rise, however, and currently look to peak on Wednesday when 850mb temperatures approach the 90th climatological percentile. This will be our next chance of reaching 90 degrees in St. Louis and Columbia, MO. It is exceedingly uncommon to not warm to that temperature this far into a calendar year, but the chances of ending that streak are fairly high (70-80%). MRB && .AVIATION... (For the 12z TAFs through 12z Friday Morning) Issued at 559 AM CDT Thu Jun 12 2025 VFR conditions will prevail through most of the TAF period, but increased moisture will eventually bring lower CIGs to the area terminals tomorrow morning. Confidence is very high (90%+) that MVFR conditions will develop, but IFR CIGs may be more scattered and transient. There will also be a fairly isolated threat for thunderstorms this afternoon, primarily in central Missouri through west-central Illinois, but confidence is not high enough in timing to use more than PROB30 wording. We may also see a few stray showers and a rumble of thunder in St. Louis today, but confidence in that is too low to include in the TAF. Conditions will be monitored for the need for amendments and TSRA inclusion. Another threat for thunderstorms appears more tangible in the St. Louis metro area tomorrow afternoon, though those terminals will be on the northern fringe of the higher chances. MRB && .CLIMATE... Issued at 620 PM CDT Wed Jun 11 2025 St Louis still hasn`t reached 90 yet in 2025. This puts 2025 in the Top 20 all time latest dates of the first 90 degree temperature, and the latest in at least 30 years (Jun 19, 1995). The all time latest first 90 degrees was July 4 in both 1961 and 1912. Records began in St Louis in 1874. Columbia has also not yet seen a 90 degree reading in 2025. The latest date of first 90 degrees on record was July 14, 1904. Records began in Columbia in 1890. Quincy reached 90 degrees on May 15 of this year. Based on the current forecast, our next best chance to see 90 degrees is around June 17. Kimble && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX