Area Forecast Discussion
Issued by NWS Jackson, KY

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015 FXUS63 KJKL 181950 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 250 PM EST Sat Nov 18 2017 .UPDATE... Issued at 1248 PM EST SAT NOV 18 2017 Some light returns are starting to pop up on the radar over the last hour, mainly across the southwestern CWA. Will go back and increase pops slightly so that isolated pops show up across more of the CWA to cover any sprinkles/light rains that may accompany these developing returns. Otherwise forecast continues to be in shape, with a small update to make sure temps, dew points, and winds were on track with the current observations. Continuing to monitor the wind/wind gust situation, but no updates have been needed thus far other than in the very near term. All updates have been published and sent to NDFD/web. UPDATE Issued at 953 AM EST SAT NOV 18 2017 Precip ahead of the main system has dissipated across the CWA leaving dry conditions, though some light rain is still ongoing across central Kentucky. Overall forecast pops seem to be in good shape so far this morning. Kept in the slight chances in the northern CWA just b/c a light shower or two redeveloping cannot be ruled out. Loaded in the latest observations for temps, dew points, and winds to make sure they were on track with the current conditions. Continuing to monitor wind gusts across the region, will make any updates as needed as we head throughout the day. All updates have been published and sent to NDFD/web. A new forecast package is not needed at this time, but a timing graphic was sent out to show the estimated arrival times of the heavier line of showers and thunderstorms late this afternoon/evening. 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...
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(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...(Monday through Saturday) Issued at 250 PM EST SAT NOV 18 2017 There is good model agreement with the evolution of the overall mean upper air pattern, but there are considerable differences in the details. This is not surprising considering we will be in a fairly progressive pattern through the coming week. The progressive pattern will result in a roller coaster pattern for temperatures from Monday through Saturday. Moisture will remain limited, with the next chance for rain not coming until next Saturday. The week will begin on a cold note, with an upper level trough axis to our east, weak upper ridging over the MS valley, and surface high pressure over the central and southern Appalachians. As the surface high shifts east from Monday into Tuesday and weak upper ridging builds over the area in advance of the next upper trough, we`ll see a quick warm up into Tuesday. That will be short lived as the next trough moves east and drives another cold front across the area Tuesday night. There will be very limited moisture with this front, and no precipitation is expected, but it will bring colder temperatures back to the area for Wednesday and Thanksgiving Day. Another warm up begins late in the week that will last into next weekend. Rain chances will return next Saturday as yet another cold front approaches the area. Looking just beyond the forecast period, indications are for another shot of cold air late next weekend.
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&& .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) ISSUED AT 100 PM EST SAT NOV 18 2017 A cold front continues to approach the region, resulting in strong and gusty southerly flow. sustained winds between 10 and 20 knots with gusts between 35 and 50 mph will be possible at all TAF sites this afternoon and evening. Isolated showers are also starting to pop up across eastern Kentucky, but should pose little concern with continued VFR VIS and CIGS. CIGS are expected to continue lowering to MVFR as the cold front nears the region late this afternoon/evening. Along the actual front, more widespread showers (and possibly an isolated thunderstorm) will occur which may lower VIS to MVFR (or possibly lower at times), passing from west to east generally between 21Z and 3Z. However light rain could linger through 6Z. Rain will continue to taper off through the rest of the overnight as winds become more westerly and entrain in drier air. Wind speeds will also quickly decrease behind the frontal passage. Dry but MVFR CIGS are expected to continue into the day Sunday. && .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 until 4 AM EST Sunday for KYZ085>088-107-109-110- 112-113-115>120. && $$ UPDATE...JMW SHORT TERM...GREIF LONG TERM...SBH AVIATION...JMW is the U.S. government's official web portal to all federal, state and local government web resources and services.