FXUS63 KLSX 182254 AFDLSX Area Forecast Discussion...Updated National Weather Service Saint Louis MO 554 PM CDT Mon May 18 2026 .KEY MESSAGES... - Widespread showers and thunderstorms are expected to continue into the evening with heavy rainfall in some locations potentially leading to flash flooding. - A few strong to severe thunderstorms are possible through the early morning hours of Tuesday with the main hazards being damaging winds, large hail, and a brief tornado or two. - Another round of thunderstorms are possible along a cold front Tuesday afternoon/evening. Damaging wind gusts and large hail are the primary threats. && .SHORT TERM... (Through Late Tuesday Night) Issued at 251 PM CDT Mon May 18 2026 Showers and thunderstorms from this morning laid out west to east on the upwind portion of the MCS. The outflow made it to a Crawford to Washington to Randolph County line before stalling. The 850 mb flow was out of the southwest this morning and has started to back from the south this afternoon. Simultaneously, a low level MCV ejected northeast out of Arkansas this afternoon. As this occurred, convection has begun to intensify on the northern side of the old outflow. Highest convective rates are currently just east of Columbia. Rainfall totals are already averaging 1 to 2 inches across the Flood Watch with isolated totals of 3 to 4 inches. This afternoon into evening, as the LLJ (or 850 mb flow) starts to slightly back and the the MCV ejects northeast convection will finally start to exit the region to the east. The break will be short lived though as another line of showers and thunderstorms will approach the region from the northwest this evening into early Tuesday morning. This line of storms will likely start to dissipate across central Missouri, but how quickly and exactly where matters regarding flood potential. The current thinking is for the line to weaken and dissipate near or just north of the St. Louis metro. However, a cold front will then approach the area from the northwest and cross the region Tuesday afternoon into evening. As this occurs, another round of showers and thunderstorms will develop. Damaging wind gusts and large hail appear to be the primary threat. After the final round of showers and thunderstorms moves across the area Tuesday evening, storm total rainfall amounts (from Monday morning to Tuesday evening) of 3 to 5 inches with isolated amounts of 6 to 8 inches appear likely. These amounts of rainfall will result in some flash flooding. Residents should monitor the latest forecasts and be prepared to seek higher ground if a Flash Flood Warning is issued for your area. BAH && .LONG TERM... (Wednesday through Next Monday) Issued at 251 PM CDT Mon May 18 2026 A surface cold front will be located across southern Missouri Wednesday with most of the region expected to be seasonably cool and dry. The one exception to this is across Reynolds, Iron and Madison counties were another round of thunderstorms will be possible close to the frontal boundary. Thursday into Friday, another mid-level wave will be located over the Mountain West with low level flow out of the southwest. As this occurs, the cold front will wash out with temperatures rising along with a return of showers and thunderstorms. The warm up will then persist into the weekend and early next week as another wave approaches from the west. This warming trend is supported by both the LREF and NBM IQRs. Looking at global ensemble guidance, a general building of mid-level heights is forecast to start this weekend across the Eastern United States and then retrograde west next week. BAH && .AVIATION... (For the 18z TAFs through 18z Tuesday Afternoon) Issued at 101 PM CDT Mon May 18 2026 Theshortwave that was over Arkansas this morning is currently over eastern Missouri with widespread convection ongoing over the St. Louis terminals. The back edge of the storms are approaching from the west, with a temporary end to the thunderstorms expected at all terminals by 8 PM. Another line of showers and thunderstorms (currently in central Kansas) is then forecast to progress into central Missouri early Tuesday morning. Now that the line has formed, have gone ahead and updated the TAFs with the latest thinking of arrival. KUIN: High confidence that thunderstorms will make it Tuesday morning between 6 and 9z. KCOU/ KJEF: High confidence that showers will make it and moderate confidence that thunder will be observed. Arrival time between 6 and 9z. KSTL/ KSUS/ KCPS: Moderate confidence that showers will make it and low confidence that thunder will be observed. Arrival time between 7 and 10z. By late morning, showers from the decaying line that originated from Kansas will be mostly dissipated. A cold front will then cross KUIN with cigs falling to MVFR/ borderline IFR. The front will then cross or be just north of KCOU and KJEF. On the cool side of the boundary expect sub- VFR cigs. For the St. Louis terminals, the thinking is the cold front will hold northwest of the area until late Tuesday afternoon. Out ahead of the cold front, another round of afternoon showers and thunderstorms will occur. The lack of confidence is on the location of the cold front and the aforementioned convection. BAH && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flood Watch through Tuesday 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 through Tuesday 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