Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 061005 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 505 AM EST Tue Dec 6 2016 .SHORT TERM...(Today through Wednesday) Issued at 438 AM EST TUE DEC 6 2016 A strong upper level low was in place across TX as of this past evening, and has quickly transitioned northeast while weakening into an open wave, now located across Mississippi as of 9Z this morning. This will continue to track northeast, moving across TN and eastern KY by this afternoon while dissipating even further, quickly exiting by 0z Wednesday. Meanwhile, the surface low pressure system is outracing the upper level wave, already pushing across TN and heading towards the eastern KY, with an expected direct impact to the CWA between 15 and 18Z today, before quickly shifting northeast out of the state. Fairly good wind sheer is taking place, with light E to SE winds ahead of the surface low, and strong W to SW winds aloft pulling in moisture from the gulf of Mexico ahead of the upper level wave. There was a pretty sharp cutoff, as was forecast, between the high clouds that were across the region, and the time at which these clouds built down and rain began. A sharp llvl inversion is also in place given the wind/temp disparity. As of now, much of the CWA has become saturated, with light to moderate rain reaching the ground. This rain is expected to continue throughout the day as the center of the surface low crosses over the region. As llvl winds begin to shift to a more southerly and then easterly direction on the backside of the surface low, midlevel winds will also become more easterly, generally after 15Z. Once this wind shift takes place, much drier air will be able to filter into the region, with the upper levels drying out by 21Z, and the mid levels following suit by 0Z this evening. This process may be delayed by an hour or two in the far east. The dry air entrainment will essentially cut off best rainmaking processes as well, though will leave a layer of moisture near the surface, stuck below a strong llvl inversion that will setup overnight. This set up looks very similar to that of the last rain system we had, which leans itself to low clouds and drizzle potential through much of the overnight instead of fog. Went ahead and added patchy drizzle into the forecast, generally tapering off from west to east as dry air filters in near the surface throughout the overnight. Temperatures are expected to fall to near freezing in many locations. While this may raise some concerns for freezing drizzle, it appears as most of the drizzle will taper off with the cooler drier winds moving in, before temperatures reach the freezing mark, thereby alleviating concerns. Dry air will continue to infiltrate the region through the day Wednesday as a broad area of surface high pressure sets in. Aloft, strong W to WSW flow will remain in place, also pulling drier air in from the central plains. This will help skies will clear throughout the late morning/early afternoon. Surface winds, while light, will generally be more northerly in direction. This will ultimately result in temperatures just below seasonable normals for afternoon highs on Wednesday, generally in the mid 40s. .LONG TERM...(Wednesday night through Monday) Issued at 505 AM EST TUE DEC 6 2016 The models are in good agreement concerning the amplified long wave pattern in place across the CONUS during the middle of the week. This regime will transition to more zonal flow through the first part of the weekend, before amplifying once again through early next week. There is more confidence in the smaller scale features through Saturday. Confidence then drops off through the rest of the extended portion of the forecast due to timing and evolution differences. A deep upper level low will shift east from Ontario to Quebec through Thursday, enabling a short wave trough to swing through the Great Lakes and Ohio Valley regions. This will bring the coldest air thus far this season into eastern Kentucky. Winds will shift to the northwest late Wednesday night into Thursday, with some light snow, although impacts looks to be minimal given the shallow depth of the moisture available and most of the better upper level support passing by further north. Highs on Thursday will be in the low to mid 30s at best, with temperatures likely dropping through the afternoon. Despite lingering cloud cover into Thursday night, lows will drop off into the teens for most locations, with highs on Friday only in the 20s. The center of the high pressure looks to pass through the region Friday night into Saturday morning. Clouds should be a bit thinner, as the flow becomes more zonal, allowing at least for some mid teens, if not lower potentially. Highs will recover back to the mid to upper 30s on Saturday. The next system will affect the area from Sunday through Monday, as a trough digs in across the Plains and then moves east, dragging a cold front across the Commonwealth. The GFS is more progressive with this system compared to its mean, with the ECMWF slower still. Have therefore allowed for a slightly slower onset of the precipitation compared to that of the blended guidance. Consequently, this also resulted into hanging onto higher pops deeper into Monday and beyond. Did allow for a small chance of a rain/snow mix for early Sunday; however, given the likely slower trend, any foreseeable impacts look too low confidence to mention at this point. Temperatures will be moderating back closer to normal through early next week, with highs back near the 50 degree mark by Monday. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) ISSUED AT 114 AM EST TUE DEC 6 2016 Conditions are beginning to deteriorate at TAF issuance, especially across the southern portion of the state. KSME has now fallen to MVFR, and KLOZ will be soon to follow over the next hour or so. High clouds still persist at the remaining TAF sites, but should begin falling quickly to MVFR generally after 8Z at KJKL and closer to 9Z at KSYM. Rainfall will be on the heals of the CIG drop, expected to start to KSME and KLOZ over the next couple of hours as well. Ceilings will likely lower further to IFR and possibly LIFR by Tuesday morning as rainfall becomes more widespread. Visibilities will also decrease to MVFR and potentially IFR as rain falls. Should see the bulk of the rain taper off by late afternoon, allowing visibilities to increase to VFR criteria. However, IFR ceilings look to be a good bet through the end of the TAF period (6Z). Winds will increase to 5-10 knots through the rest of tonight, while veering southeasterly. Will see these veer further to the west/southwest this afternoon, with speeds increasing to near 10 knots with higher gusts during the latter portion of the afternoon. All this as a cold front gets set to move through the Ohio Valley and Commonwealth. Additionally, southeasterly low level wind shear near 35-40 knots may become an issue tonight across far southeast Kentucky. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JMW LONG TERM...GEOGERIAN AVIATION...JMW

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