FXUS63 KLSX 211119 AFDLSX Area Forecast Discussion National Weather Service St Louis MO 619 AM CDT Mon Sep 21 2026 .KEY MESSAGES... - Scattered showers and thunderstorms will come to an end later this morning. - Seasonably cool temperatures are expected for the rest of the week. && .SHORT TERM /THROUGH TUESDAY/... Issued at 327 AM CDT Mon Sep 21 2026 A cold front has been moving through the area since yesterday and is now through to southeastern MO. There remains some showers and thunderstorms behind the front in the area, but they are moving east and out of the area. Some remnant showers may remain through the day today. These will be tied to the elevated front at the 850mb level and will move south as the surface front continues its trek. In the afternoon there could be some additional convective initiation along the elevated front in southeastern MO. These showers and thunderstorms are not expected to pose a threat, as the conditions for strong to severe thunderstorms are not very favorable with HREF indicating around 1500 kg/J of SBCAPE and less than 10 kts of shear. There is also weak low-level cold air advection that would limit overall development of any convection. Thanks to the cold front, the end of the relentless heat is finally here. Temperatures today will be much cooler compared to last week with high temperatures expected to be in the 60s and 70s, with some locations in the low 80s towards southeast MO. Today temperatures will be mainly driven by the presence of widespread low-level clouds, except for southeastern MO where there will be a lack of cloud cover, and the previously mentioned weak low-level cold air advection. For areas under the cloud cover, conditional climatology indicates that when ceilings are below 2 kft AGL with northerly surface winds, which is expected today, temperatures are predicted to only rise about 5 degrees from their overnight low temperature. This is what is expected to occur. Ensemble guidance has become more confident in the high temperatures in recent runs with interquartile ranges of only about 5 degrees, compared to yesterday they were 7-10 degrees. Low temperatures are expected to be upper 50s and low 60s. NBM guidance shows that Tuesdays temperatures will be similar to Monday, but southeastern MO will be joining the rest of the party with highs in the mid 70s starting on Tuesday; a much needed relief from the heat. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Issued at 327 AM CDT Mon Sep 21 2026 Seasonably cool temperatures are expected for the rest of the week. Tuesday night lows across the region are expected to be in the low to mid 50s. However, the NBM indicates there is a 30-50% chance that our northern area could drop in the upper 40s. This is possible by having an anomalously high surface ridge of 1036mb (>99% climatological percentile) over the eastern Great Lakes and southeastern Canada. Models are confident that this air mass will continue to dominate for the rest of the week with a gradual warming through the 70s, reaching the low 80s by next weekend. NBM and LREF guidance has interquartile ranges of around 5 degrees for each day this week and into the weekend. The GFS and EPS ensembles both show an upper and mid-level ridge building over the southeastern Canada region with a center of low pressure over the Ohio Valley on Wednesday. The ridge should remain fairly stationary over southeastern Canada, while the low pressure center will slowly move to the east coast of the CONUS. This pattern will allow for continued westerly and northwesterly flow aloft and northerly winds at the surface to help moderate our temperatures into next weekend and limit the moisture transported into the region. This will prevent another return of the heat and humidity in the foreseeable future; also limiting the chances for further rainfall during the coming week. && .AVIATION /12Z TAFS THROUGH 18Z TUESDAY/... Issued at 618 AM CDT Mon Sep 21 2026 IFR ceilings are starting off the TAF period at all terminals giving way to MVFR ceilings this afternoon. There is a chance that there could be some isolated showers or drizzle during the TAF period, but confidence of impact on visibility is low. There is also a low possibility of MVFR fog this morning. && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ SHORT TERM...Asel/Gosselin LONG TERM...Asel/Gosselin AVIATION...Asel/Gosselin