Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 171230 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 730 AM EST Fri Nov 17 2017 .UPDATE...
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Issued at 710 AM EST FRI NOV 17 2017 Have updated the near term grids to primarily adjust sky cover as the low stratus is really starting to erode from the southeast. This layer should be just about gone by 14z for most places. Did also add in the latest obs and trends for the T/Td grids. These have been sent to the NDFD and web servers.
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&& .SHORT TERM...(Today through Saturday) Issued at 300 AM EST FRI NOV 17 2017 07z sfc analysis shows high pressure centered just northeast of Kentucky with its influence noted in the cold temps and light northeast winds at the sfc. However, it is not enough to clear out the low clouds stuck over the CWA and is likely helping to keep them trapped. As such, the temperatures are fairly uniform across eastern Kentucky in the low to mid 30s. Dewpoints, meanwhile, vary from the upper 20s north to the mid 30s in the far southwest parts of the area. Also, thanks to the clouds, fog has been kept to a minimum. The models have come into good agreement aloft with the pattern affecting the region through the short term. They all depict benign northwest flow over Kentucky today becoming more southwesterly tonight as energy from a sharp and deepening western trough spreads quickly into the region and over the state. This will continue to be the case into the day Saturday as the progressive trough digs into the Mid Mississippi Valley looking to punch into the Ohio and Tennessee Valleys Saturday evening and overnight. Much better agreement exists among the models with this develop now than the past several runs and confidence is fairly high in a blended solution for timing and placement of the key forecast features. Even so, have favored the higher resolution guidance from the HRRR and NAM12 for weather specifics through the short term and in particular for Saturday. Sensible weather will feature the low clouds breaking up quickly just ahead of or following day break - generally from south to north. Warming will then commence with temperatures climbing smartly into the 50s and lower 60s mostly places under mostly sunny skies. For tonight, the high pressure will have retreated east in response to the approach of deep low pressure in the Plains and eventually a potent cold front. This will present a small window for radiational cooling for our valleys before thickening and lowering clouds spread in from the west. Winds will also likely kick up after midnight as the pressure field tightens and a developing warm front lifts north of the state. Cannot rule out a stray shower or two from this development tonight in the northern parts of the CWA, but most places will stay dry. Look for some limited instability to build over eastern Kentucky on Saturday in the system`s warm sector with stray showers giving way to a potential for thunderstorms in the afternoon. Some of these could become quite strong given the dynamics aloft. Additionally, winds will mix down from aloft particularly effectively with gusts to 40 mph on tap owing to the path of the sfc and 850 mb low center. The system`s cold front arrives around 00z with a convective line of showers and embedded storms anticipated dropping a solid half to 3/4 inch of rain and also helping to bring down some of the stronger winds aloft to the sfc. Would anticipate the need for a wind advisory for the entire area on Saturday - through the evening. For now, though will continue to highlight the threat in the HWO. Used the CONSShort and ShortBlend as the starting point for all the grids. Did make some adjustment to low temperatures tonight for ridge to valley distinctions. Also, beefed up PoPs with the fropa, anticipating that all places in the CWA will at least measure, and lifted the thunder potential Saturday afternoon and evening given the dynamics of the situation. .LONG TERM...(Saturday night through Thursday) Issued at 255 AM EST FRI NOV 17 2017 A strong cold front will be crossing the area at the start of the period Saturday evening with strong dynamical forcing associated with the feature thanks to a very strong 250mb jet. Very tight pressure gradient with the front and we will likely see wind gusts in the 30 to 40 mph range through at least 10 or 11 pm, before winds start to taper off late. The NAM bufr momentum transfer winds peaked right at 30 knots, which is typically the top end for wind gust potential. We will likely need some kind of wind headlines to go with this front, but way too early for those now. There is also some potential for thunderstorms, although instability is weak. However, the strong forcing alone warrants the mention of thunder. In fact would not be surprised to see a narrow line of intense showers/storms form right along the front as it tracks across the area. Any organization of storms would easily contribute to damaging wind potential, given the tremendous shear in place. We will continue to highlight wind potential in HWO and graphics. Temperatures will turn sharply colder with the frontal passage Saturday night, falling to around freezing in the highest terrain in southeast Kentucky by midnight. Models in modest agreement on some remaining moisture lingering through the night, supporting a changeover to some snow across the high terrain. With temperatures expected to reach the 20s on ridges above 3kft, some snow accumulation seems likely. Model blend actually put about a tenth of an inch of liquid on Black Mountain and this seems reasonable given the upslope flow. This would amount to about an inch of snow accumulation by Sunday morning. Temperatures at lower elevations should stay at or above freezing preventing any snow accumulations, although a few lower elevations could see a few flakes very early Sunday. GFS ensemble members provide some support to keep some snow/rain shower activity in the far east into Sunday afternoon. Cloud cover was greatly increased through Sunday given the trough hanging around. This cloud cover will keep temperatures down as well, likely preventing them from getting out of the 30s for most areas. High pressure quickly builds in for Sunday night into early Monday, setting the stage for the coldest night thus far for the fall. Temperatures in the valleys could very well reach the teens with low to mid 20s on the ridges. Temperatures will moderate as we head into next week as heights begin to rebound. Dry weather will likely persist as well with a mid level ridge crossing the region through Tuesday. A moisture starved front will cross the region on Wednesday and provide a cool down for the mid week period, but temperatures will again warm as we head into and through the holiday weekend. It looks like the weekend should at least start off dry. Some uncertainly remains over the second half of the holiday weekend that a system could impact the area and bring some rain to the area. && .AVIATION...
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(For the 12Z TAFS through 12Z Saturday morning) ISSUED AT 730 AM EST FRI NOV 17 2017 Low stratus is starting to break up more effectively over eastern Kentucky - starting in the southeast. This will clear out the IFR and MVFR cigs over the next few hours leaving VFR conditions behind for the area through the rest of the TAF cycle. High cigs will develop and lower again later tonight as a cold front approaches. Winds today will start out light from the northeast before turning to the southeast and south at 5 to 10 kts. The winds will further increase tonight from the south to southwest at 10 to 15 mph with some gustiness working in from the west late. Will need to monitor this for possible LLWS should some of the TAF sites manage to stay decoupled as the winds off the sfc pick up.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...GREIF LONG TERM...KAS AVIATION...GREIF

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