FXUS63 KLSX 191732 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1232 PM 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 18z TAFs through 18z Wednesday Afternoon) Issued at 1229 PM CDT Tue May 19 2026 Thunderstorms to the south in Arkansas have spread a thick blanket of clouds and light, high based rain showers across our region this afternoon. Beneath all of this, a cold front is pushing southeast across the region. Southerly winds ahead of the front turn to the northwest behind it. Lower ceilings also accompany the front's arrival, with most locations upstream in the MVFR range, but some areas immediately behind the front IFR for a few hours. These lower ceilings likely last through the night and into Wednesday morning before some improvement during the day Wednesday. Although there's an outside chance of a thunderstorm developing in the vicinity of the front this afternoon, the chances are too low to include in any TAF at this issuance. Kimble && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX