FXUS63 KLSX 190915 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 415 AM CDT Tue May 19 2026 .KEY MESSAGES... - Widespread showers and thunderstorms are expected to continue this morning with additional rainfall in some locations potentially leading to flash flooding. - A few strong to severe thunderstorms are possible this afternoon into early tonight ahead of a cold front. The main hazards are large hail and damaging wind gusts. && .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 414 AM CDT Tue May 19 2026 Latest analysis of radar imagery reveals a complex of thunderstorms working its way eastward across the area. Currently (as of 0730z), the leading edge of this activity is pushing into west-central IL, east-central MO, and points southwestward toward Springfield MO. Over the last few hours, this complex has gradually been weakening with eastward extent, with scattered clusters of convection along the leading edge, followed by widespread stratiform rain. Nearly all of this convection is now outflow dominant with a gust front out ahead of the leading edge producing scattered gusts up to 40mph, which has generally been tied closely to the stronger convective clusters. Steepened mid-level lapse rates (8-8.5 degrees C) and a strong 50kt LLJ are both working to keep convection semi-organized along portions of the leading edge. As a result, this complex of thunderstorms will continue to be capable of 30-40mph winds, with gusts near 50mph possible ahead of stronger convective development that percolate throughout the morning. The favorable environment highlighted above for these potential stronger convective segments is generally along and south of the I-70 corridor. As these showers and thunderstorms continue to filter into the area this morning, the threat for flooding will also continue. A majority if the area received 1-2" of rain yesterday with some locations getting 3-5", generally along I-70 and about 50 miles to the south. Locations that experienced these higher end amounts yesterday will be more susceptible to flooding today. In fact, an additional 1-2" within a 3hr period today may be enough to lead to flash flooding for some locations. High resolution guidance varies significantly on the evolution of showers and thunderstorms today, with the general consensus that showers and pockets of thunderstorms gradually wane into the late morning or early afternoon. Given all of the variables mentioned above, the risk of heavy rainfall has prompted us to continue the Flash Flood Watch, which is now in effect until this afternoon. Residents should continue to monitor the latest forecast and be prepared to seek higher ground if a Flash Flood Warning is issued for your area. Latest surface analysis reveals a surface low lifting northeast into WI, with a cold front stretching southwestward into northwest MO. This front is modeled by guidance to gradually slide southeast throughout the morning, approaching northeast MO by late this morning. Ample low-level CAA and thick stratus behind the front will mitigate the severe weather threat in the post-frontal airmass. Uncertainty remains with how quickly the atmosphere will be able to recover this afternoon/evening. Lingering showers and ample clouds will lower the severe risk or push the risk further south, while less showers/clouds would increase the risk and lead to a more widespread severe storm threat this afternoon/evening. Regardless, instability and mid-level flow are still forecast to be sufficient enough to support organized storms with potential for large hail, and damaging wind gusts. Any lingering outflow boundaries from convection this morning may serve as areas of focus for thunderstorm development this afternoon ahead of thecold front. Peine && .LONG TERM... (Wednesday Night through Monday) Issued at 414 AM CDT Tue May 19 2026 Low-level cold air advection along with potential lingering cloud cover, within the post-frontal airmass, will lead to much cooler conditions for Wednesday, with highs forecast to be around 10-15 degrees below average. Quasi-zonal flow aloft encompasses the region through the end of the week, which should allow for a period of dry conditions until Friday. By the end of the week, long-range guidance shows a southern stream shortwave lifting northeast and merging into the downstream end of a northern stream longwave trough near the Great Plains. Low-level flow ahead of these features appears to remain easterly, which would limit moisture return along with rain chances. Regardless, the evolution of these features leads to the return of rain chances Thursday night into Friday, with the LREF 6hr probabilities for accumulated precipitation reaching a widespread 80% on Friday for the area. Chances for precipitation look to remain limited this weekend as probabilities stay below 20% for a majority of the area. A gradual warmup is also forecast as LREF temperature IQRs increase to temperatures right around climatological normals by next week. Peine && .AVIATION... (For the 06z TAFs through 06z Tuesday Night) Issued at 110 AM CDT Tue May 19 2026 A weakening complex of thunderstorms is currently pushing eastward into the area, with the leading edge of strongest convection stretching from near Quincy MO to just east of Columbia MO. Behind the leading edge of convection, widespread stratiform rain with occasional lightning is being observed. KCOU/KJEF just went through the leading edge with KCOU reporting a wind gust to 33kts and brief IFR visibilites/MVFR ceilings. As a result, within the stronger convection, brief IFR visibilites/MVFR ceilings are expected. This complex of convection is forecast to continue weakening with eastward extent, resulting in lower confidence of impacts at the St. Louis metro terminals. As of now, the leading edge is forecast to arrive between 07-08z with around a 30% chance for IFR visibilites/MVFR ceilings. Lingering stratiform rain is forecast for several hours behind the convection, with visibilities forecast to stay P6SM, aside from heavier showers that may briefly result in MVFR visibilites. A cold front approaches from the northwest early this morning with MVFR/IFR ceilings expected just ahead of and behind this front. Confidence in IFR ceilings is highest at KCOU/KJEF/KUIN, with potential for below airport minimums on Tuesday, as indicated by the mention of the TEMPO group. Currently, MVFR ceilings are forecast for the St. Louis metro terminals, with the lowest ceilings (<1kft) forecast to stay to the west. Confidence also remains low with how quickly ceiling improve later this evening and into the night, with guidance generally improving conditions around 06z tonight. Ahead of the cold front, southerly winds will prevail, however, gusty and variable winds related to showers and scattered thunderstorms will be possible. Behind the cold front, northerly surface winds are forecast to prevail across the area by later this evening and continue into Wednesday. Peine && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flood Watch until 1 PM CDT this afternoon for Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO- Jefferson MO-Lincoln MO-Moniteau MO-Monroe MO-Montgomery MO- Osage MO-Pike MO-Ralls MO-Saint Charles MO-Saint Louis City MO-Saint Louis MO-Warren MO-Washington MO. IL...Flood Watch until 1 PM CDT this afternoon for Bond IL-Calhoun IL- Clinton IL-Fayette IL-Jersey IL-Madison IL-Marion IL-Monroe IL-Saint Clair IL-Washington IL.&& $$ WFO LSX