059 FXUS63 KLSX 181758 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1158 AM CST Wed Jan 18 2017 .UPDATE... Issued at 1033 AM CST Wed Jan 18 2017 Complicated clearing trends this morning. Skies are clearing quickly over the central part of CWA including the St. Louis metro area underneath a low level inversion as moisture depth is relatively shallow. Farther to the north and west moisture depth is deeper delaying the clearing. Do still expect mid-high clouds to stream back into the central and southern part of the area this afternoon ahead of the upper low over the Central Plains. These cloud trends will cause a disparity in temperatures today where more sun means warmer temperatures and more clouds mean cooler temps. Britt && .SHORT TERM... (Through Late Tonight) Issued at 345 AM CST Wed Jan 18 2017 The synoptic pattern early this morning features shortwave ridging stretching along the MS River, in between a compact/potent trough across the Ohio Valley and another longwave trough/cutoff low over the Desert Southwest. The upper-level low over the Southwest will eject out into the Central Plains by Thursday morning, bringing the next chance of precipitation to our region. Widespread cloud cover continues to plague the region this morning, with little eastward push of the clearing line noted in the past hour or so. This is likely due to the weak lower-tropospheric wind fields given the ridging both at the surface and aloft. Taking these trends into account, think fog will be hard to come by this morning, thus have removed mention from most of the area this morning. Additionally, have kept cloud cover in through more of the day today, also lowering highs a couple degrees given the expected lack of solar insolation. The surface ridge should push east by this afternoon, allowing southerly flow to commence. This may allow for just enough mechanical mixing to break up some of the low cloud cover across portions of central/northeast Missouri late this afternoon, allowing for a late surge of temperatures into the lower 50s. For tonight, the aforementioned upper-level low will slide into the Central Plains which will allow for deep southwesterly flow to set up over the region. Moisture transport within this regime will commence late tonight into early Thursday morning, bringing showers northeast into the region. Very weak elevated instability is also noted across far southeast MO, thus have included a slight chance of a thunderstorm in this region after 09Z Thursday. KD .LONG TERM... (Thursday through Tuesday) Issued at 345 AM CST Wed Jan 18 2017 Overall, the extended fcst features an active upper air pattn along with unseasonably warm sfc temperatures (10-20 degrees above average). The GFS and ECMWF are still in disturbingly good agreement through 198 hours, but with just enough inter-model disagreement to avoid a plunge into the atmospheric science version of the uncanny valley. The aforementioned upper low will become negatively tilted as it lifts through the region on Thu/Thu night, bringing showers and isolated thunderstorms to the area. PW values of 0.8-0.9" are at +2 SD for January and similar to PW values noted last weekend. There will probably be some moderate downpours similar to what was observed at times during last weekend's freezing rain event, but this time without the freezing. Temperatures will be well into the 40s and 50s. A smaller disturbance intensifies across the south-central plains on Fri and then lifts northeastward on Fri night and Sat. Moisture appears to be limited with this system, and the best lift will be north of the area. Another upper disturbance will move over the southwestern CONUS this weekend and induce sfc cyclogenesis over TX/OK. The low pressure system intensifies and moves eastward/northeastward into the southeastern CONUS and Ohio Valley late this weekend and early next week, bringing a chance of rain to mostly the southern half of the CWA. Yet another upper disturbance induces yet another sfc reflection over the central plains early next week, and the resulting low pressure system then moves northeastward towards the Great Lakes. This system may bring a chance of rain to parts of the area on Tue/Tue night. Kanofsky && .AVIATION... (For the 18z TAFs through 18z Thursday Afternoon) Issued at 1138 AM CST Wed Jan 18 2017 Large area of clearing has developed around the St. Louis area terminals with VFR conditions now expected through afternoon hours into the evening. The clearing line is now close to KCOU, and VFR conditions will likely develop there early in the afternoon. KUIN will likely take longer to go VFR as the clearing line is slightly farther away. MVFR ceilings that are currently over southern Missouri will likely move back into the area this evening as moisture streams back into the area ahead of the storm system. Showers will develop over the area late tonight and tomorrow as this system moves through Missouri and Illinois. SPECIFICS FOR KSTL: VFR conditions are expected through early evening before MVFR ceilings redevelop. Moisture will stream back into the area causing MVFR ceilings and visibilities to develop tonight as well as showers as a storm system approaches the area. Showers and IFR conditions are expected on Thursday as this system moves across the area. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX