017 FXUS63 KLSX 221048 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 548 AM CDT Sun Sep 22 2019 .SHORT TERM... (Through Late Monday Afternoon) Issued at 330 AM CDT Sun Sep 22 2019 Main focus for this forecast continues to be the potential of locally heavy rainfall through this evening. Have not made any changes to going Flash Flood Watch. Latest regional mosaic continues to show showers and thunderstorms developing across northern Missouri and central Illinois. This convection will increase in areal coverage this morning across central and northeast Missouri as well as west central Illinois as the low level jet increases in strength which will subsequently increase moisture convergence in the 925-850mb layer. This is where the greatest rain chances will be confined through midday until a shortwave trough currently over the Rocky Mountains will move east into the Great Plains. This will increase large scale ascent over Missouri and Illinois as well as cause the cold front to move east which will cause the showers and thunderstorms to move southeast across the CWA this afternoon and this evening. Will continue with likely/categorical PoPs as strong moisture converge ahead of the cold front will be juxtaposed with right entrance region of an upper jet streak. There will still be the potential for flash flooding in the watch area given the high values of PWATS and deep warm cloud layers making for efficient rainfall producers, particularly with any training thunderstorms in the nearly parallel flow aloft. There will also be the potential for a few strong to severe thunderstorms this afternoon and this evening. The NAM is depicting a pre-frontal trough moving across the CWA where the atmosphere will become moderately unstable with deep layer shear. Latest CAMS runs have been consistent in showing a few stronger cells developing over eastern Missouri into southwest Illinois during peak heating. Large hail and damaging winds will be the primary threats. Showers and thunderstorms will continue to move southeast and out of the CWA late tonight. Monday is expected to be dry as the front moves south of the area and an upper ridge builds into Missouri and Illinois. Britt .LONG TERM... (Monday Night through Saturday) Issued at 330 AM CDT Sun Sep 22 2019 Dry weather is still expected Monday night into Tuesday as an upper ridge and surface high moves across Missouri and Illinois. The global deterministic models and the GEFS mean are in relatively good agreement that shortwave trough and attendant cold front will move through the Midwest on Wednesday and Wednesday night. There may be a few strong storms across parts of central and northeast Missouri as well as west central Illinois on Tuesday night ahead of the cold front where there will be a sufficient combination of instability and shear. It still appears that this front will move back north through the area as early as Thursday in response to cyclogenesis over the High Plains as a upper trough deepens over the western CONUS. This will result in a chance of showers in thunderstorms over the area from Wednesday into Friday. Temperatures Tuesday through Saturday will remain at or above normal based on GEFS mean temperatures and forecast 850mb temperatures around 15C. Temperatures during the workweek will fluctuate by a few degrees depending on frontal passages and rain chances. Britt && .AVIATION... (For the 12z TAFs through 12z Monday Morning) Issued at 541 AM CDT Sun Sep 22 2019 Showers and thunderstorms are expected to move into KUIN and KCOU this morning and the St. Louis area terminals this afternoon. These thunderstorms will produce moderate to occasional heavy rain and MVFR and IFR ceilings and visibilities before moving out of the terminals tonight. Winds will be out of the south and gust at times to 20kts before a cold front causes winds to shift out of the northwest this evening. SPECIFICS FOR KSTL: Mainly dry and VFR conditions are expected through late morning. Then showers and thunderstorms are expected to move into the terminal this afternoon. These thunderstorms will cause moderate to occasional heavy rain and MVFR and possible IFR ceilings and visibilities before moving out of the terminal overnight. Winds will be out of the south and may gust at times before a cold front causes winds to shift out of the northwest tonight. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flash Flood Watch through late tonight for Audrain MO-Boone MO- Callaway MO-Knox MO-Lewis MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Pike MO-Ralls MO-Shelby MO. IL...Flash Flood Watch through late tonight for Adams IL-Brown IL- Pike IL. && $$ WFO LSX