Area Forecast Discussion
Issued by NWS Jackson, KY

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353 FXUS63 KJKL 181205 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 705 AM EST Sat Nov 18 2017 .UPDATE... Issued at 645 AM EST SAT NOV 18 2017 Did a quick update to the grids to fine tune the PoPs early this morning. Also, adjusted temperatures as the valleys have just about mixed out. These have been sent to the NDFD and web servers. && .SHORT TERM...(Today through Sunday) Issued at 310 AM EST SAT NOV 18 2017 07z sfc analysis shows a tightening sfc pressure gradient through the Ohio Valley ahead of a rapidly developing low pressure system over central Missouri. This is resulting in breezy conditions just off the sfc and a few southerly wind gusts to 20 mph for our western counties at the moment, but lighter winds are found in the east with the valleys calm under an inversion. In those valleys, despite increasing high clouds through the evening, many manged to effectively decouple and radiate down closer to dewpoint temperatures in the lower 30s. These are slowly starting to warm back up, but mid to upper 30s are still noted. Elsewhere, the better mixed sites are reporting mid 50s. Dewpoints vary from the upper 20s in a few of the higher elevation points to the northeast while values near 40 exist to the west and south. On radar, a few light returns are noted but not much is likely making to the ground given the drier conditions of the boundary layer. The models are in good agreement aloft through the short term portion of the forecast and the dynamic system set to move across the area today and tonight. A large trough will quickly consolidate over the Southern Plains this morning moving into the Mid Mississippi Valley region and then Tennessee Valley by nightfall. As it does so, plenty of energy will run through the bottom of the trough and right across Kentucky punching through the JKL area between 7 pm and midnight. The accompanying height falls will pass through by 06z with heights rebounding a bit in its wake into Sunday morning. A trailing shortwave does move over the area Sunday afternoon and this will help to usher the system out of here. Just minor differences are noted with the models as this impactful system passes so confidence in most of the details is relatively high. As such, have favored the short term model blends while leaning most heavily on the highest resolution ones like the HRRR and NAM12. Sensible weather will feature lowering clouds and winds picking up from west to east this morning with advisory level winds possible by early afternoon. These windy conditions from the south to southwest will continue through the evening as a cold front approaches and passes through eastern Kentucky. There should be just enough instability ahead of the boundary for a convective line to form with some embedded thunderstorms. The strongest of these could tap into the strong wind field aloft to bring down damaging winds. As a result, much of the JKL CWA is in a marginal risk for severe weather per SPC. Will keep this highlighted in the forthcoming HWO and social media graphics. A little more than a half an inch of rain can be expected for most of the area as the front moves through. Winds will then switch to the west and northwest staying strong and at wind advisory level through midnight. After that, though, the winds will start to subside with colder air advecting into this part of the state with falling temperatures and upslope flow into Sunday morning. This is expected to result in a mixing of light pcpn with snow showers or flurries for a time before drier air takes over from west to east later in the morning ending all but the last lingering traces in the far east by afternoon. With the snow potential only the eastern ridges will have a shot at accumulations though warm ground temperatures will negate much of this before it ends. As such, just have a small amount - less than a 1/2 inch on the highest points (but close to 1" on top of Black Mountain) down to a trace on the lower elevation ridges. A chilly day will follow for Sunday under mostly cloudy conditions and continued CAA on northwest winds. Used the CONSShort and ShortBlend as the starting point for all the grids, though did make significant changes to beef up the winds and gusts today into the evening. Also, kept the PoPs maxed out as the front crosses this evening rather than having them drop back into the 80 percentile range per the blends tonight. Finally, for Sunday lowered the highs a notch and allowed for more lingering light pcpn (ra/sn) than implied by the model blends. Will continue the wind advisory as outlined by the day shift. .LONG TERM...(Sunday night through Friday) Issued at 245 AM EST SAT NOV 18 2017 High pressure will build in Sunday night and settle over the area by Monday morning. This will bring an end to lingering clouds as we head through the night. Sunshine will return in force on Monday allowing for a modest warm up after a very cold start. With clear skies and good radiational cooling Sunday night, temperatures may start off in the upper teens to lower 20s Monday morning. A bit of uncertainty in the forecast as we head through Tuesday and Tuesday evening regarding the strength of a shortwave trough. 00z ECMWF has trended stronger with the trough and is not producing a few showers over the region, while the 00z GFS continue to drop the energy off to our south, with little moisture in place for any showers. The blended model solution came in dry, so opting to stay with the dry forecast for now. However, would not be surprised to see some small rain chances emerge late Tuesday or Tuesday evening in future updates. Still some model differences on how things evolve towards Thanksgiving, as the GFS develops a storm system off to our southeast, but keeping it out of our area. This would bring subsidence over eastern Kentucky from Wednesday through Friday as this system impacts areas to our southeast. This would likely mean colder mornings and drier afternoons for fire weather concerns. However, ECMWF solution isn`t quite on board with the GFS, so still lots of uncertainty on temperatures. Confidence in higher on a dry forecast through Saturday. There does appear to be a chance of a clipper system to push across the area late next weekend, but its still beyond the extent of this forecast update. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) ISSUED AT 705 AM EST SAT NOV 18 2017 VFR cigs will continue through most of the day, though cigs will continue to lower, ahead of a cold front approaching from the west. Scattered showers will be about the area this morning, mainly north and west of the TAF sites. South southwest winds will then increase to 10 to 20 kts, with gusts of 25 to 35 kts during the day on Saturday. More widespread showers and potential thunderstorms will be moving in after 18z. Ceilings/visibilities will lower down to MVFR by the end of the period for most sites, as the cold front moves on across eastern Kentucky and winds switch to the northwest - equally strong for a time. && .JKL WATCHES/WARNINGS/ADVISORIES... Wind Advisory until 1 AM EST Sunday for KYZ044-050>052-058>060- 068-069-079-080-083-084-104-106-108-111-114. Wind Advisory from 10 AM this morning to 4 AM EST Sunday for KYZ085>088-107-109-110-112-113-115>120. && $$ UPDATE...GREIF SHORT TERM...GREIF LONG TERM...KAS AVIATION...GREIF is the U.S. government's official web portal to all federal, state and local government web resources and services.