839 FXUS63 KLSX 100007 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 707 PM CDT Tue Oct 9 2018 .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 336 PM CDT Tue Oct 9 2018 Main concern in the short term continues to be the strong cold front that will slide through the region late tonight through Wednesday. Latest HRRR is beginning to come into better agreement with what is actually happening over region as of 20z. Ahead of system, scattered showers and thunderstorms are developing in a moderately unstable environment with surface based CAPES in excess of 1500 J/kg and effective bulk shear 30+ kts over portions of central/northeast Missouri as of 20z. This initial round of activity is more diurnally driven so should see showers and storms diminish a bit towards sunset. However, the break in activity will not be long as more significant storms develop along prefrontal trof over central Missouri after 02z Wednesday and track east through forecast area during the late evening and early morning hours. There will be plenty of instability and shear late into the evening for a few strong to severe thunderstorms over portions of central/northeast Missouri as well as west central Illinois. SPC has kept this area in a slight risk with the main threat being damaging winds, though isolated tornadoes and large hail are possible. Then another round of activity to fire along main cold front after 08z Wednesday over western Missouri and track eastward through forecast area during the day on Wednesday. With progressive nature of system, rainfall amounts will remain below flash flood criteria, though could see between half an inch and an inch of rainfall through Wednesday afternoon before system exits region. As for temperatures, another mild night tonight with lows only in the mid to upper 60s. On Wednesday, highs will be in the upper 60s to upper 70s, with steady or falling temperatures during the afternoon hours most locations. Byrd .LONG TERM... (Wednesday Night through Next Tuesday) Issued at 336 PM CDT Tue Oct 9 2018 Strong surface ridge to build into region Wednesday night with scattered showers exiting region. Ridge will usher in much colder air with lows in the upper 30s to upper 40s Wednesday night. Highs on Thursday will only be in the low 50s to low 60s, which are 10 to 15 degrees below normal for this time of year. By Thursday night, even colder temperatures can be expected with lows in the mid 30s to low 40s. This cold air combined with little or no winds and clear skies could allow for the formation of patchy frost across northern portions of forecast area. However, confidence is low as a quick moving shortwave to approach region towards daybreak on Friday, so should see increasing clouds. Left out mention of patchy frost for now. Upper level shortwave to slide through region on Friday undercutting surface ridge. Even though moisture will be limited, isolated/ scattered showers will develop by midday and slide quickly east through forecast area, exiting by early Friday evening. Beyond that, better chances of rain will move into the region Saturday evening and persist through Sunday night before exiting Monday morning. Still some differences in timing, strength and duration of the rain for the weekend as a southern stream shortwave slides through region just south of forecast area Saturday night through Sunday morning and a northern stream system slides through region Sunday night. No major changes to ongoing forecast at this time. Below normal temperatures to persist through remainder of forecast period. Byrd && .AVIATION... (For the 00z TAFs through 00z Wednesday Evening) Issued at 646 PM CDT Tue Oct 9 2018 Low pressure over the eastern Plains will strengthen and move northeast tonight and Wednesday. This will push a cold front east through Missouri into Illinois through Wednesday afternoon. Expect waves of showers and thunderstorms ahead of the front tonight into Wednesday, with the first wave moving through central and northeast Missouri this evening. While prevailing conditions this evening and into the early overnight hours should stay VFR, any shower or thunderstorm will be capable of producing lower ceilings and visibilities in heavy rain. There will be a general lowering of ceilings and also expect an increase in coverage of showers and thunderstorms Wednesday morning as the cold front moves into central and eastern Missouri. Expect widespread MVFR ceilings and visibilities, and some IFR is also expected with the showers and storms. Some lingering MVFR ceilings and showers will likely persist behind the front Wednesday, but there should be a general improving trend after the front passes during the afternoon. Wind should shift sharply from the south to the west as the front passes. SPECIFICS FOR KSTL: Expect VFR flight conditions to prevail at Lambert through the evening and into the pre-dawn hours of Wednesday morning. Most model guidance holds the bulk of the rain back until after 10Z Wednesday morning, but I cannot totally rule out a few showers or thunderstorms before that. Expect ceilings to drop ahead of the front on Wednesday morning when most of the rain rolls in. Current thinking is prevailing low end MVFR ceilings with occasional MVFR visibilities in the heavier showers or storms. There is a possibility that ceilings could drop to IFR, but confidence is low at this time so did not go that low in the TAF. Latest model trends are pushing the front through Lambert around 18Z on Wednesday. Should see a general decrease in precipitation and rising ceilings after the front moves through. Wind will turn sharply from the south-southwest to the west when the front passes through the terminal. Carney && .PRELIMINARY POINT TEMPS/POPS... Saint Louis 70 76 46 60 / 60 90 5 0 Quincy 66 70 41 54 / 90 90 5 0 Columbia 64 68 40 56 / 90 80 0 0 Jefferson City 67 70 42 58 / 90 80 0 0 Salem 68 79 48 59 / 40 100 20 0 Farmington 68 76 45 61 / 40 90 5 0 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX