087 FXUS63 KLSX 100529 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1229 AM CDT Wed Oct 10 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 06z TAFs through 06z Wednesday Night) Issued at 1211 AM CDT Wed Oct 10 2018 A line of showers with a few embedded thunderstorms continues to move slowly east through central and northeast Missouri into east central Missouri and west central Illinois. This slow progression eastward is expected to continue through the rest of the night and into Wednesday. Heavy showers embedded in the line will be capable of intermittently dropping visibility and ceilings to IFR. However, think flight conditions will generally stay MVFR with the line of showers. Most guidance fills in low ceilings after 12Z ahead of the cold front with heights down below 2000 feet. The front will move through from east to west from around 15Z in central Missouri to around 20-22Z. There should be a general improvement to VFR during the afternoon after FROPA. Southerly flow ahead of the front will turn sharply to the west after the front passes. SPECIFICS FOR KSTL: The line of showers moving into east central Missouri will likely be to the terminal by 08-09Z. There are a few embedded thunderstorms which will be capable of reducing visibilities to IFR levels, and ceilings could drop below 2000 feet in these storms as well. More shower activity is expected in the morning with ceilings dropping below 2000 feet ahead of the front. Latest guidance has the cold front moving through the terminal between 18-19Z, and other than a stray shower that should be the end of the precip. Ceilings should begin rising behind the front as well and I expect VFR flight conditions by late afternoon or early evening. Carney && .PRELIMINARY POINT TEMPS/POPS... Saint Louis 44 60 41 58 / 20 0 0 10 Quincy 39 54 36 52 / 10 0 0 40 Columbia 39 56 37 54 / 0 0 0 50 Jefferson City 41 58 38 57 / 0 0 0 40 Salem 45 59 39 58 / 40 0 0 10 Farmington 44 61 40 59 / 20 0 0 10 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX