264 FXUS63 KLSX 220450 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1150 PM CDT Sun Oct 21 2018 .SHORT TERM... (Through Late Monday Afternoon) Issued at 305 PM CDT Sun Oct 21 2018 Early this afternoon, northwest flow aloft prevails over a very dry atmospheric column with an area of surface high pressure having settled over southeast Missouri and the lower Ohio River Valley. The result has been clear skies with a south to southwest surface wind, as temperatures climbed into the 50s. Despite the full solar insolation, max temperatures will still be around 10 degrees below normal. Northwest flow aloft will continue through Monday afternoon and, as a result, will struggle mightily in the moisture department in helping to juice up the column any. Southwest surface winds will continue into Monday as another cold front drops down from the north Monday afternoon and into the night. While a modest moisture increase may result at the low levels, it will be too little and too shallow to have any real impact on rain chances that could be brought about by the cold front moving through. As such, we expect the cold front to result in minimal rain chances. Min temperatures tonight will not be as cold as last night due to prevailing south to southwest winds, although the best opportunities to decouple will be south of Saint Louis in valley regions and due to proximity of the surface high. Temperatures in these areas should still drop into the low-mid 30s, with lower 40s expected for areas in the prairie regions northwest of Saint Louis thanks to a bit stronger wind. A few wispy thin cirrus clouds may be possible but overall skies should still be clear. Max temperatures on Monday will be noticeably warmer, with many areas poking above normal by just a few degrees. With full or nearly full sunshine once again expected, along with west to southwest surface winds, temperatures should take full advantage of a warmer morning start and climb well into the 60s, with a few spots along the I-70 corridor in Missouri touching 70 degrees. Per the discussion from the late morning update, many locations dropped into the mid to upper 20s last night in the Freeze Warning area, and this appears to have ended the growing season for 2018. TES .LONG TERM... (Monday Night through Next Sunday) Issued at 305 PM CDT Sun Oct 21 2018 The overall longwave upper pattern for North America is not expected to change much during this period. A longwave upper RIDGE will be situated over the west and a TROF over the east, resulting in a northwest flow aloft over our region. The longwave positions will shift a bit during the period, however. It will be during some of this shifting, when a split flow regime briefly takes hold over the central CONUS, that will allow some strong upper level systems to drive down and give us our best opportunity for rainfall during the next seven days. Otherwise, the northwest flow aloft will give us our usual dry weather due to limited moisture infusion. Operational models are in pretty good agreement with each other and with their previous runs on the timing of the strong upper level systems dropping into our area during the period of split flow aloft late this week, with rain chances beginning Friday night and continuing into Saturday night. Available moisture will be largely what the system can draw into it and aloft, and for now, worth mid- range (about 40-50%) PoPs. As confidence increases on the occurrence and track of these systems, can see this increasing into at least likely category eventually. Otherwise, temperatures will tend to be below normal for much, if not all, of this period. The flow aloft will be conducive to cool air intrusions and allow little opportunity for a sustained southerly surface flow. TES && .AVIATION... (For the 06z TAFs through 06z Monday Night) Issued at 1142 PM CDT Sun Oct 21 2018 The main issue overnight remains the potential for LLWS at KUIN. A west-southwesterly low level jet centered around 0.5 km AGL is becoming established from northeast KS across northern MO into west central IL. This low level jet is expected to result in LLWS conditions from around 06-13z at KUIN. Otherwise VFR flight conditions are expected through the forecast period with periodic thin high clouds. Southerly surface winds tonight will veer to southwesterly on Monday morning. Surface winds will shift to the northwest in the wake of a cold front that will move through northern MO and western IL on Monday afternoon and through central and eastern MO early Monday evening. SPECIFICS FOR KSTL: VFR flight conditions are expected through the forecast period with periodic thin high clouds. Southerly surface winds tonight will veer to southwesterly on Monday morning. A weak cold front will move through the terminal on Monday evening resulting in a northwest wind shift. Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX