032 FXUS63 KLSX 210916 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 416 AM CDT Wed Aug 21 2019 .SHORT TERM... (Through Late Thursday Afternoon) Issued at 415 AM CDT Wed Aug 21 2019 Primary focus in the short term continues to be convection the effects the precipitation and clouds will have on temperatures. A cold front currently over Iowa will drift slowly south today through Thursday. Persistent south-southwesterly flow at 850mb will continue to drive warm and moist air up into the mid Mississippi Valley. RAP, GFS, NAM and ECMWF all show persistent 850mb moisture convergence over the forecast area on the 850mb baroclinic zone, and the models all print out QFP coincident with this moisture convergence. Additionally, the convection allowing models (CAMs) all show simulated thunderstorms developing over central/northeast Missouri this morning where the moisture convergence is, and periods of storms continue to affect the area through Thursday to a greater or lesser extent depending on which model you look at. This solution matches well with the mass fields on all of the short term guidance. I've therefore kept high chance to likely PoPs across northeast Missouri into west central Illinois this morning, shifting south late this afternoon and tonight into Thursday as the front and corresponding low level baroclinicity also drifts south. Model precipitable water is in excess of 2 inches due to the continuing warm moist flow aloft...although model QPF is not particularly high...1-1.5 inches over the next 48 hours or so. Additionally, the storms in the CAMs are progressive over our area, and do not train for long periods over one area. Therefore I'm not too worried about widespread flooding, but will mention a possibility for locally heavy rain as a nod to the high P-wats. All of this convection should produce plenty of cloud cover over the area today. I think this will suppress temperatures...even where it doesn't rain...so I've leaned toward the more moderate end of guidance and have not issued any heat headlines this morning. If the precipitation and cloud cover doesn't work out of course, then there could be excessive heat issues this afternoon. Carney .LONG TERM... (Thursday Night through Tuesday) Issued at 415 AM CDT Wed Aug 21 2019 The cold front will continue taking its sweet time moving south through the mid Mississippi Valley on Thursday night and Friday. While the effective surface front may be continually pushed a little further southward with each round of convection, the low level baroclinic zone remains parked over Missouri and Illinois since the upper level trough never seems to dig far enough into the Mississippi Valley to truly get us into northwest flow aloft. The continual south-southwest 850mb flow into the baroclinic zone, combined with a series of eastward moving MCVs left over from nocturnal convection over the Plains, will keep the chance of precipitation going through Friday into at least Friday night. Medium range models differ on the position of the front Saturday and Sunday. The ECMWF is the furthest south and southwest...most likely due to it's somewhat deeper upper level trough stretching from New England southwest through the Ohio Valley into the Tennessee Valley. The GFS is much faster moving this upper trough offshore and it develops an upper level ridge over the Upper Midwest and Great Lakes with another short wave moving east from the Plains into the lower Mississippi Valley Saturday and Sunday. The GFS therefore prints out precip across much of southern Missouri Saturday, and southeast Missouri and southern Illinois on Sunday. Both the GFS and ECMWF move the front back to the north of the forecast area Monday, but the ECMWF pushes another cold front through Iowa into Missouri Monday night and Tuesday as another large upper level low moves across south central Canada and the upper Midwest. The upper pattern on the GFS is quite different. In the wake of the Saturday/Sunday shortwave, a 5950 meter 500mb ridge builds across the eastern Plains into the Mississippi Valley by Tuesday afternoon. The differences in the guidance for Saturday through Tuesday make this a low confidence medium range forecast. Carney && .AVIATION... (For the 06z TAFs through 06z Wednesday Night) Issued at 1147 PM CDT Tue Aug 20 2019 VFR conditions, dry weather, and light S-SW surface winds are expected at the TAF sites through the next few hours. A cold front to our northwest will make a push into the region beginning around daybreak Wednesday and continue through Wednesday afternoon, with several rounds of showers and storms developing along it and affecting the TAF sites. Surface winds will veer NW with frontal passage, but there is also some concern that this frontal boundary will stall late Wednesday and into Wednesday night, maintaining the rain threat well into Wednesday night. Where the front should push the farthest south from, KUIN, there is increasing potential for a period of low clouds to intrude on Wednesday morning and have added that to the TAF. SPECIFICS FOR KSTL: VFR, dry weather, and light S surface winds until Wednesday morning when the first of several rounds of showers and storms looks to affect the terminal. While there should be an initial cold FROPA in the afternoon, a stalled front near the terminal late in the day could result in a more variable wind direction. The threat for showers and storms looks to continue well into Wednesday night. TES && .PRELIMINARY POINT TEMPS/POPS... Saint Louis 87 70 83 70 / 60 70 60 50 Quincy 84 64 79 63 / 60 60 50 30 Columbia 86 67 80 66 / 60 70 70 50 Jefferson City 86 68 82 67 / 60 70 70 50 Salem 87 69 82 65 / 50 60 60 60 Farmington 90 68 82 66 / 50 60 70 50 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX