210 FXUS63 KLSX 122337 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 637 PM CDT Thu Jun 12 2025 .KEY MESSAGES... - Widespread showers and a few thunderstorms will plague much of the region tonight through the first half of the weekend, bringing some locally heavy rainfall. - Our first run of temperatures in the 90s looks likely for the middle of next week. && .SHORT TERM... (Through Late Friday Night) Issued at 1242 PM CDT Thu Jun 12 2025 A slow-moving upper level low will be the main focus of the short term period. Latest satellite and radar imagery show widespread cloudiness, with a few showers affecting central MO. Forcing for ascent ahead of a northward moving vorticity lobe rounding the upper-level low will keep the best threat of showers in central and northeast MO through the rest of the day into this evening. Instability has been limited due to the widespread cloudiness, but can`t completely rule out an isolated storm in central/northeast MO through this evening. Attention turns to the southwest overnight as the main upper-level low meanders over the region. A weak surface reflection will bring enhanced low-level convergence, coupled with the forcing from the low aloft, resulting in fairly widespread showers overnight into early Friday. Therefore, I have upped pops from the previous forecast. Coverage of showers will wane a bit late Friday morning, which might allow for some limited diurnal heating by early Friday afternoon (through a thick cirrus shield and a broken lower cloud deck). Even with the limited heating, we should realize around 500-1000 J/kg of MLCAPE which should be just enough to promote a few more robust showers and some scattered storms. With fairly deep warm cloud depths, these showers will be pretty efficient rain makers. In fact, the HREF LPMM suggests some isolated locations may see up to two inches of rain. That being said, they should be moving enough to not cause too many widespread concerns for flooding. Nothing severe is expected given very poor lapse rates and weak deep-layer shear. Coverage should wane a bit from west to east Friday night as the upper level low continues to meander to the east and the loss of diurnal instability should limit thunderstorm chances, but showers will likely persist especially in IL. Deitsch && .LONG TERM... (Saturday through Next Thursday) Issued at 1242 PM CDT Thu Jun 12 2025 The pesky upper-level low will finally begin to rotate off to the east by Saturday. That being said, lobes of vorticity will continue to rotate around the backside of the low, keeping enough upper-level ascent in place to foster showers in our Illinois counties, with less coverage expected the further west you go into Missouri (especially by the afternoon/evening). Given the deep, saturated soundings, lapse rates are quite poor thus instability is limited. That being said, a few lightning strikes are possible here and there as showers bubble just deep enough to initiate ice and charge separation. Given deep warm cloud depths, any shower will be efficient rain makers but I think there will be enough breaks in between rounds of showers to limit any flood potential. The upper-level low will finally push well to the east by Sunday. As it stands now, Sunday looks like a generally dry day. However, with temperatures warming back into the mid 80s, enough instability will be around and there are some hints of a subtle wave moving around the backside of the departing low which could be just enough to spark a few isolated showers/storms in a generally uncapped environment. The pattern turns more zonal, and then more southwesterly aloft through midweek next week. This will allow for generally warming temperatures, along with at least some threat of shower/storm complexes. The most favored times for these complexes look to be late Sunday/Monday morning, and then again Tuesday night into Wednesday. That being said, timing out these threats in a zonal flow pattern are notoriously challenging, so these windows are likely to change. The severe threat looks fairly low through Monday, but the mid/upper level flow does increase a bit by midweek thus I think the potential for some more organized convection exists Tuesday night and beyond. This increasing threat is supported by the NCAR/CSU ML guidance. I also think our run at dodging the heat is likely to come to an end next week. The latest ensemble guidance suggests highs likely to exceed 90 degrees (70-80% chance) by Tuesday into Wednesday of next week. This will push heat index values well into the 90s, perhaps approaching 100 degrees at times next week (depending on storm timing). Deitsch && .AVIATION... (For the 00z TAFs through 00z Friday Evening) Issued at 634 PM CDT Thu Jun 12 2025 A slow moving area of low pressure will gradually track toward the region from the southwest spreading showers and perhaps a few thunderstorms across the area. These showers become more numerous overnight and into the day on Friday with ceilings gradually lowering to MVFR or perhaps even IFR through the morning. While showers are expected, confidence in thunderstorms is considerably lower. If any breaks in the clouds can form on Friday, then better instability will develop and lead to more thunderstorms in the afternoon. Kimble && .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