FXUS63 KLSX 190026 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 726 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 627 PM CDT Mon May 18 2026 Most of east-central Missouri and along I-70 in western Illinois have observed multiple rounds of showers and thunderstorms today. An MCV has been the impetus for this redevelopment of showers and thunderstorms this afternoon into evening. It has also finally dislodged the training showers and thunderstorms with convection approaching the Mississippi River and rainfall coming to an end behind. Highest convective rates are currently just southwest of St. Louis, with rainfall totals now averaging 2 to 4 inches, locally 4 to 5 inches, across the Flood Watch. There is also a threat for a quick spin up tornado or two along with mostly sub- severe hail. The weak tornado threat is due to an outflow that stalled near Crawford to Washington to St. Francois Counties. We have also had a few storms with elevated cores just below severe limits. This is likely due to the ~7 degrees C/km mid-level lapse rates. Convection will clear the area by 10 PM. The end of the showers and thunderstorms will be short lived though as another line of showers and thunderstorms has already formed across central and eastern Kansas. This line of showers and thunderstorms will continue to slowly move east overnight and weaken across central Missouri. Damaging wind gusts and a brief tornado or two will be the primary threats. How quickly the line weakens remains the primary question. The overall thinking is that the line will weak substantially by the time it reaches I-70 near Columbia, MO. The weakening of the line is due to the displacement of the showers and thunderstorms out ahead of the cold front. The surface cold front will likely be just northwest of Columbia, MO Tuesday morning and stall near a Columbia, MO to Quincy, IL line through mid-afternoon. Behind the cold front, the chance of precipitation and severe weather is low, while ahead of the cold front another round of showers and thunderstorms appear likely. Surface based CAPE is forecast to be in the 2500 to 3000 J/kg range with around 30 to 40 kt of SFC to 6 km shear. The best shear looks to be offset from the best instability, or behind the surface cold front. Hodographs due show some cyclonic curvature in the lowest levels, but it is weak. Most of the forcing will also have to come from the surface cold front. Given the above, the environment does appear to br supportive for some supercell development, with some storm splitting possible. As such, the Storm Prediction Center has the region southeast of Columbia, MO to Havana, IL in a slight risk for severe storms. 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. As such, have expanded the flood watch until Tuesday afternoon. 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 00z TAFs through 00z Tuesday Evening) Issued at 620 PM CDT Mon May 18 2026 The shortwave 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