Area Forecast Discussion
Issued by NWS Jackson, KY

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089 FXUS63 KJKL 041018 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 518 AM EST Sun Dec 4 2016 .SHORT TERM...
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(Today through Monday) Issued at 408 AM EST SUN DEC 4 2016 Light precip has encompassed our southern CWA and is continuing to slowly work its way north as it overcomes a layer of llvl dry air. Temperatures across the CWA are above freezing so far this morning, so all precip should be falling as rain, even if some wet bulbing is occurring. However, can`t rule out some of the higher elevations(generally above 2k ft) still seeing some snowflakes mix in as temperatures will be a tad bit cooler here at onset, and they could possibly tap into colder air aloft as well. Overall, continued to slow down pops through this morning based on the latest radar and hi-res model trends. It also looks like there may be more of a break into the afternoon, with a defined southern extent of rain pushing eastward of the state, and a secondary northern extent moving in after 21Z. Kept chance pops in otherwise during this time and into the overnight. Between about 6Z and 10Z (starting in the east), dry air really begins to pull in aloft as the upper level forcing starts pushing east of the region and allows cooler drier flow into the region. This will limit saturation to the lower levels, supporting more of a drizzle event, before the dry air continues to quickly cut off remaining precip potential by dawn Monday. Lows Monday morning should remain just above normal, generally in the upper 30s across the CWA. Low level clouds will likely persist throughout the day Monday as winds near the surface will be from a more NE to E direction compared to the Wrly flow in the mid and upper levels, keeping lingering moisture trapped near the surface for much of the day. A strong upper level low located across TX during the day Monday will begin to track northeastward as we head into the extended portion of the forecast. As this occurs, expect another strong pull of Gulf moisture into the Ohio Valley region, with a surface low pressure system rotating across Louisiana. This will result in high clouds building into the region once more from south to north throughout the day Monday and will help boost temps to just above seasonable normals in the afternoon despite cloud cover. While precip chances should generally hold off until after 0Z Tuesday, there is still a small potential that some pops could overcome mid level dry air between 18Z Monday and 0Z Tuesday, mainly along the TN border. As such, did include slight chance to low-end chance pops here for this time frame. .LONG TERM...(Monday night through Saturday) Issued at 518 AM EST SUN DEC 4 2016 Models solutions are in reasonably good agreement with the general mid/upper level pattern through the extended but continue to differ significantly with details in the strength and timing of several features embedded within an overall progressive flow. This results in even larger differences in sensible weather later in the forecast. Mid/upper level cut off low moving out of Texas early in the period opens up into a wave as it passes through the region Tuesday. The GFS is slightly slower and stronger with this first disturbance compared to the more similar ECMWF and Canadian. This system will provide a soaking rain to the area with models spitting out about an inch of rainfall on average, mainly from Monday night through Tuesday. Forecast soundings do hint at some marginal, very elevated instability Monday night. Mid/upper level lapse rates do steepen a bit between about 10k and 22k feet. In general CAPE remains below 100 J/kg. But there is substantial shear within this layer as well, on the order of 30 to 50 kts. So while one could not totally rule out a faint rumble of thunder, feel the overall threat is low enough that any mention of thunder was left out of the forecast for now. However, will pass on to upcoming shifts for monitoring. Forecast gets quite tricky thereafter as a series of disturbances rotate around a low pressure system residing along the Northern Tier and southern Canada. A shortwave trough swings through the region sometime towards the end of the week, most likely Thursday, as models present a range of possibilities with respect to the timing and strength of this trough. Details of sensible weather are not any clearer but the GFS and Canadian continue to advertise a more similar solution with the ECMWF a much warmer and wetter outlier, bringing a surface low and heavier precipitation in the form of rain across the Commonwealth. The faster GFS solution ushers colder air into the area at a much quicker pace and hints at the possibility of some light isold to scattered snow shower activity. The Canadian, being a colder solution similar to the GFS keeps our weather dry. Until models begin to show better agreement and/or show some solid trends will continue to rely heavily on the model/guidance blends which suggest that a wintry mix of precipitation will be possible through that time frame depending on the time of day/night. On a more certain note, much colder air does eventually move into the area for Friday and next weekend. Thus any precipitation that does fall will transition to just snow Thursday night into Friday with the potential of some lingering upslope snow shower activity into early Friday morning. Wouldn`t be surprised if future forecasts extend the snow shower activity into Friday proper or even Friday night, as this is type of scenario is typically handled poorly by the larger scale synoptic models. At this point do not expect anything more significant than minor snow accumulations at best, and if that.
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&& .AVIATION...(For the 06Z TAFS through 06Z Sunday night) ISSUED AT 103 AM EST SUN DEC 4 2016 Very tricky forecast overnight and into the day tomorrow. A mid/upper level wave is expected to impact the TAF sites through the forecast period, however surface high pressure remains at the surface with a layer of dry air in place in the low levels. IR SAT does show high clouds penetrating eastern KY as the system continues to approach, and should continue to stream across the region overnight. These clouds are expected to thicken and lower, but based on latest trends, this may occur a bit later than originally expected. As of the 6Z TAF issuance, VFR conditions are expected to persist through 12Z at the southern sites KSME and KLOZ, but will quickly deteriorate after this point to MVFR throughout the day as moisture finally overcomes the llvl dry layer, and rain chances set in. This will occur a couple hours later at KJKL and KSJS and closer to 18Z at KSYM. Llvl clouds will linger throughout the upcoming night as well, possibly lowering further to IFR, even as precip chances begin to taper off. Overall, winds should remain light and variable throughout the period. && .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...JMW LONG TERM...RAY AVIATION...JMW

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