Area Forecast Discussion
Issued by NWS Jackson, KY

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124 FXUS63 KJKL 212132 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 432 PM EST Sat Jan 21 2017 .SHORT TERM...(This evening through Sunday night) Issued at 432 PM EST SAT JAN 21 2017 A large and deep low pressure system will track east across Kentucky during the period, bringing wet weather and possibly thunder. Models have had trouble honing in on the details of what`s going to happen. Although runs from 24 hours ago seemed to back off on heavy rain threats, recent runs from last night and today have again pointed to a heavy rainfall potential, especially near the Virginia border. An ESF statement is issued for this. The matter was chatted about with MRX, and the decision was made to hold off on any flood watch until there was more certainty. In terms of synoptics and forecast details- the surface low is being largely driven by a powerful upper level system moving east out of the southwest CONUS. There is actually not much baroclinicity present considering how strong the surface system will be. A warm front being drawn north by the system should reach KY before being overtaken an occlusion and the low itself moving eastward. A band of overrunning precip along/north of the front is expected to move north over KY on Sunday. A relative lull should arrive from south to north once this passes by. Models show weak instability, largely after the deep moisture has passed by. Can`t rule out some thunder during this time, but have kept it at only a slight chance. On Sunday night, deep moisture returns under the upper low and comma head. This is when models contain the heaviest precip. Forecast soundings are nearly moist adiabatic but mostly stable. This coincides with persistent strong upward vertical motion. if models persist and show better convergence on a wet solution, a flood watch may still be needed. .LONG TERM...(Monday through Saturday) Issued at 330 PM EST SAT JAN 21 2017 The extended forecast period begins on Monday with a deep closed upper low tracking northeast through the spine of the Appalachians. As this feature tracks northeast, blocking over the New England and Canadian Maritime region will hinder the exit of the back edge precip moving through eastern Kentucky. This slow exit followed with the approach of the colder air in behind on Monday night into Tuesday may lead to a brief mix of rain and snow on top of Black Mountain. In addition to this, models have been coming into more agreement of a prolonged heavy rainfall event coming to an end Monday evening into Monday night across eastern Kentucky. Some lingering minor flood problems may be possible, if not just some rivers running full. Both the Euro and GFS seem to have come to an agreement on this with the Euro being slightly wetter. Will keep this mention in the HWO. Heading into the midweek time frame, a brief period of ridging moves into the OH valley with a period of drying as southwest flow increases ahead of the next incoming cold front. High temps on Wednesday will climb into the upper 50s to low 60s with SW 10 to 20 knot winds bringing in an unseasonably warm airmass. In fact, models are suggesting an overall drying trend to the approaching front with the bulk of the moisture to the north over the Midwest and into Ohio. Little if any precip is expected with this feature. Passage of the front on Wednesday night will bring in a colder airmass to the region by Thursday with a possible prolonged upslope event taking shape for Thursday and Friday. At this point the pattern brings in a longwave trough across the eastern CONUS into the weekend. The northwest flow then brings a series of disturbances in an upslope scenario. At this point, while the models hint at temps being warm enough for rainfall during the day and snow showers overnight, an upslope event with the correct wind component would mean some convection and snowfall at warmer temps. For now, went with a general snowfall at 34 degrees and below due to the uncertainties in the models but this may need reevaluated. The general trend is cooler towards the end of the extended but models have backed off from the depth of the cold air. Due to this, will leave any mention of snow out of the HWO as none is expected to be impactful at this point. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) ISSUED AT 1255 PM EST SAT JAN 21 2017 VFR conditions are expected to prevail until late tonight, with mainly mid/high level ceilings. A bit of light rain will affect far southeast KY this afternoon, and possibly near/north of I-64, but it should not offer up much in the way of restrictions. The next round of more significant weather will not arrive until late tonight. Showers and lower ceilings are expected to spread into the JKL forecast area from the southwest before dawn on Sunday. The worst conditions should be in the far west and southwest, with at least MVFR if not IFR occurring on Sunday morning. Further east, drying downslope flow will work to erode the lowest clouds, and the eastern tip of the state should remain VFR. However, there still could be some showers even in the far east before the end of the period. A few thunderstorms can`t be ruled out in the southern part of the area by mid day on Sunday. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...HAL LONG TERM...SHALLENBERGER AVIATION...HAL is the U.S. government's official web portal to all federal, state and local government web resources and services.