889 FXUS63 KLSX 092041 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 341 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 18z TAFs through 18z Wednesday Afternoon) Issued at 1214 PM CDT Tue Oct 9 2018 Diurnal cu have developed in a region of moderately unstable conditions with surface based CAPES in excess of 1000 J/kg and effective bulk shear approaching 30kts especially over portions of central/northeast Missouri. So will see showers and thunderstorms develop and track north through this area. Added vicinity thunderstorm mention at KCOU after 20z Tuesday and around 00z Wednesday at KUIN. Rest of TAF sites to remain dry and VFR through first half of forecast period. After initial activity diminishes, will see better chances of showers and thunderstorms with a prefrontal trof that will slide across the region late this evening and into the overnight hours. MVFR ceilings and visibilities can be expected with the storms. Showers and storms will persist through the morning hours on Wednesday as main cold front slides through region. Otherwise, main forecast issue will be the winds. Gusty south winds will begin to veer to the southwest by mid morning on Wednesday. The front will move through KUIN by 16z Wednesday with winds veering to the west and picking up. SPECIFICS FOR KSTL: Even though diurnal cu have developed across the STL metro area, expect VFR ceilings and dry conditions through 07z Wednesday. Prefrontal trof to approach KSTL after 07z Wednesday with increasing chances of showers and thunderstorms. MVFR ceilings and visibilities can be expected with the storms. Gusty south winds will veer to the southwest and diminish a bit after 14z Wednesday. Cold front will slide through KSTL around 20z Wednesday with winds veering to the northwest and becoming gusty once again. Byrd && .PRELIMINARY POINT TEMPS/POPS... Saint Louis 70 76 46 60 / 40 90 5 0 Quincy 66 70 41 54 / 80 90 5 0 Columbia 64 68 40 56 / 90 90 0 0 Jefferson City 67 70 42 58 / 90 90 0 0 Salem 68 79 48 59 / 30 100 20 0 Farmington 68 76 45 61 / 40 90 5 0 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX