FXUS63 KLSX 191348 AFDLSX Area Forecast Discussion...Updated National Weather Service Saint Louis MO 848 AM CDT Tue May 19 2026 .UPDATE... Issued at 842 AM CDT Tue May 19 2026 Convective complex continues to nudge southward into Arkansas this morning with stratiform rain spreading through central Missouri and occasionally as far east as the Mississippi River. We have given some consideration to canceling the Flood Watch early as rainfall rates in the stratiform rain region have been quite minor. However, some convective redevelopment along the front noted in southwest Missouri behind the stratiform rain indicates we can still get some higher rainfall rates if this convection spreads northeast. So we will maintain the Flood Watch until expiration at 1PM, but the overall threat is much more limited at this point than it was yesterday. Latest update to the Day1 Convective Outlook from SPC also has shifted the severe threat southeast with the idea that the clouds and stratiform rain will limit instability ahead of the front today until the front arrives near our southeastern CWA border late this afternoon. This is consistent with our thinking as well as the severe weather threat is greatly reduced, with the remaining threat tied to redevelopment of instability ahead of the front which may take quite some time considering the clouds and rain this morning. Kimble && .KEY MESSAGES... - Showers and thunderstorms continue today with a more limited chance of severe thunderstorms or flooding compared to prior days. - Cooler and less humid weather arrives behind today's cold front. The next round of more widespread showers and thunderstorms is Thursday night into Friday. && .SHORT TERM... (Through Late Tonight) 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 the cold front. Peine && .LONG TERM... (Wednesday Morning 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 12z TAFs through 12z Wednesday Morning) Issued at 654 AM CDT Tue May 19 2026 A broad region of showers with occasional lightning mostly across MO continues to slide southeastward with the heaviest precipitation across central/south-central MO. For KCOU/KJEF, showers with isolated embedded thunderstorms are possible through 16z, while KUIN and the St. Louis metro terminals should experience on and off showers through 15-16z. Most of the showers will not impact visibilities, with the exception of heavier showers/thunderstorms that may lead to brief MVFR visibilities. There is a low chance (30%) for isolated thunderstorms this afternoon/evening near and south of the St. Louis metro, which has led to the inclusion of a PROB30 group. Highly variable ceilings accompany the area of showers with scattered pockets of very low ceilings, around 500ft, underneath the more broad and consistent 6-10kft cloud deck. A majority of these scattered ceilings near 500ft have been across central/northeast MO with more widespread ceilings of this nature to the north and west near a cold front that is across western MO/southern IA. As this cold front approaches today, ceilings are forecast to lower at all terminals with widespread low MVFR/IFR ceilings expected across the area. Ceilings at below airport minimums are possible, with the best chance for this at KCOU/KJEF, followed by KUIN, with a low chance for impacts to this magnitude at the St. Louis metro terminals. Guidance has continued to indicate that conditions are slow to improve, with possible impacts from low ceilings lasting into the day on Wednesday. Southerly surface winds around 10kts veer to the north behind a cold front that passes from north to south today with northerly winds prevailing into tomorrow. 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