Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 300752 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 252 AM EST Wed Nov 30 2016 .UPDATE...
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Issued at 251 AM EST WED NOV 30 2016 Aside from blending latest obs into the forecast, have also begun to incorporate 00z model runs into the forecast. Full short term updated discussion will be issued shortly. UPDATE Issued at 1026 PM EST TUE NOV 29 2016 Convection continues to blossom and fill in across the TN valley. Fortunately, most of the organized cells are having a hard time maintaining their integrity as they make their way north. Eastern Kentucky remains stable at the surface and the latest meso- analysis has only meager MU CAPE values just to our south. Despite the low level jet ramping up overnight, it is unlikely that storms will be organized enough to take full advantage of this jet and overcome the stable surface layer. As such, have downplayed the severe threat for the rest of the overnight and have only mentioned some strong wind gusts still possible. Freshened up the hourly pops through tomorrow based on the latest higher resolution model trends. This yielded slightly less QPF for the Bluegrass, and perhaps a touch more across portions of the Cumberland Valley, as some training of storms will be possible closer to dawn. Updates have been sent. UPDATE Issued at 722 PM EST TUE NOV 29 2016 Convection has commenced in earnest down in the deep south. Dew points across eastern Kentucky are currently running from the low to mid 40s across most locations. Thicker cirrus will advect in from the southwest through this evening; however, some of the cooler valleys have taken advantage of the drier low level air and nearly calm winds. Temperatures have dropped into the lower 50s, so have allowed for a few upper 40s as a possibility, before thicker cloud cover moves in and allows for a rise later on. The last few runs of the HRRR have held pops off until closer to 04 or 05z. Given the drier air in place, am inclined to agree with the slower arrival and have reflected this in the pop timing. Updates have been sent.
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&& .SHORT TERM...(This evening through Wednesday night) Issued at 437 PM EST TUE NOV 29 2016 A strong upper level low is in place across MN this afternoon, with deep longwave troughing across much of the central conus. A strong ridge is also in place across the southern Gulf of Mexico. The difference between these two systems is producing strong pressure gradients, especially across the southern Mississippi and Ohio River valleys. Meanwhile, a strong surface low pressure feature is in place across Minnesota as well, in conjunction with the upper level low. This surface low has two cold fronts protruding southeastward. The first of these cold fronts is now east of the region, having impacted us last night, however the secondary cold front is gaining strength as it pushes eastward toward the Ohio River Valley overnight. Strong southerly flow is in place, with winds expected to continue increasing as the cold front nears. Moisture will also be on the increase ahead of the front this evening and through the overnight. Given the latest sounding profiles, this increase in moisture and WAA is still strong support for elevated instability just ahead of the front, with elevated thunderstorms possible generally between 3 and 6z across our western CWA. Some of the heavier rain showers could result in the mixing down of strong winds aloft, so damaging winds cannot be ruled out. Surface based instability will begin increasing after midnight as a meso-low quickly pushes eastward ahead of the front and into the region as well. This will result in higher winds transferring to the surface, and a good potential for scattered thunderstorms across the area. Latest forecasts soundings show highest winds transferring to the surface between 6 and 12Z, so it won`t be hard for high to damaging wind gusts to occur. The largest threat, as outlined by SPC in their slight risk area, will be along I75 and points westward in our CWA. However, this does not rule out the isolated potential for damaging winds elsewhere either. Also based on the sounding profiles, the storms will likely pass over as a QLCS, in line form. Given this type of profile, with the very strong winds, and impressive low level sheer, an isolated spin up tornado cannot be ruled out along the front of the line. The actual cold front will continue eastward across the CWA through just after 18Z, before it exits to our east. Rain, chances for thunderstorms, and potentially gusty winds will continue through the day Wednesday, though the damaging wind threat and tornado threat will diminish as a low level inversion sets up. Still the potential that some gusty winds could make it to the surface in the heaviest showers and thunderstorms. In better news, this system will bring with it a good shot of Gulf moisture and soaking rains. Almost the entire CWA is expected to see an inch of rain or more from tonight through tomorrow evening, with some locations across the southwest possibly topping 1.5 inches. This will hopefully help with any ongoing drought concerns, as well as any ongoing wildfires. Rain chances will finally taper off through tomorrow evening as the cold front continues to exit east of the region and high pressure starts to take hold. By this point the upper level low and the surface low pressure system will be moving across the Great Lakes region, with northerly flow on the back side makings its way into the Ohio River Valley. This will result in much cooler overnight temps compared to tonight, much closer to seasonal norms. .LONG TERM...(Thursday through Tuesday) Issued at 438 PM EST TUE NOV 29 2016 The period is expected to begin with an area of broad troughing across much of the CONUS and southern Canada with ridges over the Atlantic and Eastern Pacific. At the sfc, a slow pressure system is expected to be tracking through Quebec and the Northeastern CONUS with the trailing cold front moving off the eastern seaboard at that time with sfc high pressure nosing into the area. A mid level low over the Great Lakes with associated shortwave trough south into the Lower OH Valley is also expected early in the period. Thu through Friday, the closed low is expected to meander into Eastern Canada while a shortwave initially over the Norther Rockies moves south to the Four Corners region and closes off. The 12Z model runs seem to be in better agreement in handling this with a slower and generally less consolidate system. Height rises are expected over the OH Valley especially on Friday with sfc high pressure settling across the area. Late Friday through Sunday, a series of northern stream shortwaves are expected to move from the Rockies/Northern Plains east to the Great Lakes and OH Valley with the strongest of these nearing the Mid Valley and Lower OH Valley late Saturday night. This pattern would lead to a sfc wave moving across the southern states with inverted trough north into the area on Sunday with chances for mainly light precipitation. At the same time, the closed low is expected to dig further south into Northern Mexico from the Four Corners and then track across Northern Mexico. During this period, lowered pops compared to the Superblend for Saturday into Saturday night as it was biased up by the 0Z ECMWF run and did not reflect the model consensus with the upper air pattern/closed low with the 12Z runs and past few GFS runs. High pressure is then expected to bring a lull in precip chances for late Sunday or Sunday night into most of Monday. However, rain chances should return with the potential for another wetter system with more Gulf of Mexico moisture possibly getting involved as the closed weakens, opens up, and interacts with a trough moving across the Canadian Maritimes and Western CONUS. At the surface, a low pressure system should develop over TX or the Western Gulf of Mexico region and track toward the Lower OH Valley Monday into Tuesday. As for sensible weather, plenty of moisture is expected to remain near 850 mb and below to start the period with potential for diurnally driven cu and or lingering stratocu. This and cold 850 mb temperatures should lead to below normal highs Thu into Friday, but diurnal ranges will be a bit limited. Clouds should thicken and lower late Saturday night into Sunday with light preciptation possible. Depending on how quickly the lower levels saturate a rain and snow mix might be possible early on Sunday. However, the better chance of preciptation with this system will hold off until during the day on Sunday when the atmosphere will have moderated further and precipitation should fall as rain. As already noted, Sunday night and Monday should be mainly dry although there will be some passing mid and high clouds from time to time. Monday night into Tuesday rain chances will return with the surface low moving into the Lower OH Valley region. && .AVIATION...
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(For the 06Z TAFS through 06Z Wednesday night) ISSUED AT 251 AM EST WED NOV 30 2016 Conditions range from VLIFR to VFR at the start of the period. The worst conditions were generally in the southeast part of the forecast area near the VA border. Rain was falling in most places. Looking for rain to persist into Wednesday morning, with a deterioration to a mix of mostly MVFR and IFR. Rain should taper off for all but perhaps the eastern tip of the state early in the afternoon, with a return to VFR forecast. However, there will likely be a return to MVFR ceilings by late in the day (although, there is not high confidence in this). An eventual return to VFR for all areas is expected by the end of the period.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...HAL SHORT TERM...JMW LONG TERM...JP AVIATION...HAL

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