478 FXUS63 KLSX 191803 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1203 PM CST Tue Nov 19 2019 .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 324 AM CST Tue Nov 19 2019 The surface low associated with the clipper system early this morning was located over western Illinois with a trough axis extending nearly due southward along the Mississippi River. Shower activity has waned over the past couple of hours and limited slight chance PoPs early this morning along/east of the aforementioned trough axis. The remainder of the day should be characterized by decreasing cloudiness from west to east along with seasonable temperatures. Coolest readings are forecast to be across south-central Illinois due to lingering clouds into the early afternoon. High temperatures will only reach the upper 40s in these locations. Further southwest, an earlier clearing should lead to highs reaching the upper 50s to near 60 degrees for portions of central and southeastern Missouri. Fog should develop late tonight, mainly along/east of the Mississippi River. These areas are favored for the development of fog due to the expected timing of the departure of stratus today, as well as light and variable winds expected near a surface ridge of high pressure. The current expectation is for visibilities to stay largely above 1 mile, but if clearing is delayed a few hours than currently forecast, some patchy dense fog may be possible in west-central and/or south-central Illinois. Outside of fog development, a mostly clear sky along with temperatures near to slightly above normal for the date are forecast. Lows tonight should be mainly in the 30s across the bi-state region. Increasing clouds are expected on Wednesday ahead of the next weather system ejecting out of the Rocky Mountains. The timing of the onset of rain has continued to slow down compared to a couple of days ago, with the daylight hours on Wednesday likely staying dry areawide. Increasingly southeasterly winds will help yield moderating temperatures compared to those of today. Look for highs to reach the upper 50s to mid 60s across the area which is fairly close to the warmer MAV MOS numbers. Gosselin .LONG TERM... (Wednesday Night through Monday) Issued at 324 AM CST Tue Nov 19 2019 (Wednesday Night - Friday Night) Widespread shower activity remains very likely Wednesday night, mainly ahead of the approaching cold front in a region of strong low- level moisture advection. Rainfall amounts do not appear too high due to the relatively short duration of rainfall. Amounts generally should be around a quarter to a half inch for most locations. Also cannot rule out a rumble of thunder as the most aggressive model guidance suggests some low MUCAPE values and Showalter indices near 0 late Thursday night. However, still feel that the probability of occurrence is too low to explicitly mention with this forecast package. The cold front will slowly progress through the CWA on Thursday with diminishing chances of any shower activity behind it. Another round of rain appears increasingly likely Thursday night perhaps into early Friday north of the slow-moving cold front. Added likely to low categorical PoPs as far north as the I-44/I-70 corridors in Missouri and Illinois respectively. This area of rainfall will be supported by strong synoptic forcing via low-level moisture advection, mid/upper level diffluence, and vorticity advection ahead of the closed low entering the south-central Plains. Uncertainty in the forecast increases beginning on Friday as the deterministic ECMWF progresses the cold front further southeastward than the GFS/CMC. In addition, the closed low ejecting out of the Rockies into the south-central Plains is weaker. Consequently, very little precipitation is depicted from Friday through Friday night on the ECMWF. This solution was not favored with this forecast package, but also cannot be discounted at this time. The more realistic and likely scenario is for continued light rain early on Friday focused across southern sections of the forecast area. Additional precipitation may then spread northeastward associated with the approaching closed low. This precipitation would start off as rain, but as the temperatures cool in the lower portions of the atmosphere the rain should mix with and changeover to snow. This should occur from parts of central Missouri northeastward through west-central Illinois. Farther southeast, the vast majority of any precipitation should be in the form of a cold rain. Light accumulations of wet snow still could be in the offing for northwestern sections of the forecast area if the stronger GFS/CMC solutions are on the right track. Temperatures will start off this period very mild ahead of the cold front. Lows Wednesday night should be in the upper 40s to low 50s. Highs on Thursday should warm nicely into the low to mid 60s as well. For reference, these temperatures would be about 10 degrees above normal for the date. Behind the cold front, a return to below normal temperatures is expected. Lows both Thursday and Friday night will mostly be in the 30s and highs on Friday are only forecast to be in the low to mid 40s. (Saturday - Monday) A fairly quiet, benign weather pattern appears in the offing for this upcoming weekend into early next week with northwest flow aloft. Dry weather is favored along with moderating temperatures. After initially starting off on the cool side on Saturday/Saturday night, return flow around a departing surface ridge of high pressure should lead to temperatures climbing back into the 50s for Sunday and Monday. Gosselin && .AVIATION... (For the 18z TAFs through 18z Wednesday Afternoon) Issued at 1144 AM CST Tue Nov 19 2019 Primary concerns will be centered around gusty winds today. A northwest to southeast oriented low level jet of 30-40 kts will be aligned approximately along the Mississippi River through the afternoon. As dry air filters into the region from the northwest, ceilings continue to break west to east. This will introduce winds aloft to the surface with gusts around 20 knts through early evening. The next question will be the need to address potential fog development tonight. Shallow inversions and light/variable winds east of the Mississippi River could lead to reduced visibility early Wednesday morning. Otherwise, as skies clear today, VFR conditions are expected to extend through most of the period. SPECIFICS FOR KSTL: Much of the period is expected to be VFR with the main concerns related to gusty winds today and fog potential tonight. A 30-40 kt low level jet will be positioned overhead through the afternoon with increased mixing from resulting sunshine. This has resulted and will continue to result in surface gusts around 20 kts through sunset. Winds will die off tonight with potential for fog primarily east of the Mississippi River. Potential become limited further west. Therefore, stuck with 6SM mention with the opportunity to make later adjustments, if needed. Clouds will continue to work back in from the west through the later half of Wednesday. There are signals for LLWS very late in the period with greatest risk after the period. For now, left the mention out to be assessed in later updates. Maples && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX