Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 051738 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1238 PM EST Mon Dec 5 2016 .UPDATE... Issued at 1238 PM EST MON DEC 5 2016 Based on the latest model data, needed to delay precipitation onset across eastern Kentucky by a few hours across the board. The zone forecast text product update that was just issued will reflect no precipitation in eastern Kentucky until between 1 and 2Z this evening. The QPF and weather type grids were also updated to reflect this change. UPDATE Issued at 1001 AM EST MON DEC 5 2016 The forecast is on track so far today. Mostly cloudy to cloudy skies will persist through the end of the day, as one area of low pressure aloft continues moving off to our east, and another approaches from the southwest. The area should remain rain free until 22 or 23Z, before the next batch of rain begins moving in. Have ingested the latest obs data into the forecast grids to establish new trends. Aside from that, no other changes to the forecast were deemed necessary. UPDATE Issued at 704 AM EST MON DEC 5 2016 Overall forecast seems to be in pretty good shape. Low clouds continue to linger across the region Did adjust the temperature curve a bit through this morning as temperatures did not drop quite as low as originally forecast through the overnight. This included loading in the latest observations for temps, as well as the dew points, and winds. All changes have been published and sent to NDFD/web. No updates to the forecast package will be needed at this time. && .SHORT TERM...(Today through Tuesday) Issued at 403 AM EST MON DEC 5 2016 As the mid/upper level wave that impacted the area yesterday continues to shift northeast of the region, more zonal flow is taking hold with surface high pressure moving eastward across the state. That being said, MVFR clouds continue to plague much of the region under a pretty steep inversion that has set up. Dry air will continue to filter in aloft and in the mid levels throughout the day, eventually working its way down to the surface and allowing the low cloud deck to mix out, generally after 15 to 18Z. Attention then turns to a strong upper level low positioned over southern TX this afternoon. At the surface, the center of low pressure will be located just off the TX/Louisiana coast, but will continue to push northeastward throughout the day following the upper level low, quickly reaching Mississippi by this evening, and TN late tonight, before traversing eastern KY and eastern TN during the day tomorrow. This will push the center of high pressure currently across the state to our northeast, and allow deeper moisture to quickly begin filling into the state from the south, reaching our southern CWA between 21Z and 0Z this afternoon/evening. That being said, upper level winds will continue to pull moisture into the region well ahead of this system, so even as the low clouds begin to mix out today, high clouds will already begin building in ahead of this system. Overall, it is not likely that we will see much of a break in the clouds throughout the day as a result. According to the latest forecast soundings from the NAM12, the transition from high clouds to moisture build down and precip will be very quick. Only slight chance pops are in the forecast along the TN border before 0Z, but widespread rain is expected to encompass the entire southern half of the CWA by 6Z, and and the entire eastern portion of the state by 12Z. A steady rain is expected to continue throughout the day Tuesday. Still not seeing enough support for instability, even aloft, to include thunder at this time. The upper level low is expected to decrease in strength, becoming an open wave by the time it moves over eastern KY. As the surface low pressure center moves across the CWA in the afternoon, drier air will be quick to filter in behind, weakening the surface low and cutting off best rain potential. As such, rain is likely to end just as quickly as it started, with only low end chances expected across far eastern KY by 0Z Tuesday. While temperatures today will be near seasonable normals despite cloud cover, the surge of warmer moist air into the region will actually boost temps well into the 50s for the day tomorrow. .LONG TERM...(Tuesday night through Sunday) Issued at 510 AM EST MON DEC 5 2016 Models are finally showing better agreement with mid/upper level features through the extended and have even seen some trends towards better agreement in sensible weather elements. A broad trough moving through the Intermountain west at the start of the period will reach the Ohio Valley Wednesday night, passing through during the day Thursday. The 0Z GFS and Canadian, having been the more consistent runs, are a bit stronger with the mid level features of this system than the 0Z ECMWF. Regardless the boundary layer and sfc features associated with this disturbance are quite weak. Timing is similar with all solutions now, with the ECMWF only slightly slower. Overall trends are for lower pops and less QPF potentials. However, this system will still usher in some very cold air into the region, with H850 temperatures bottoming out close to -15C. The high pressure system building in behind this disturbance will settle down directly over the Commonwealth Friday night, allowing temperatures to drop into the low to mid teens by Saturday morning. Would not be surprised if morning lows flirted with some single digits Saturday in our typically colder valley spots. Thereafter return flow develops rather quickly, pulling plenty of moisture northward back through the MS valley and into the OH. If initial indications are correct, fairly strong isentropic lift will bring overspreading precipitation back into our area as early as Sunday. Too early to capture details at this time, but with the cold air in place imagine that precipitation will probably fall as a wintry mixture at the onset early Sunday morning before transitioning to just rain through the day. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) ISSUED AT 1238 PM EST MON DEC 5 2016 Widespread cloud cover will persist across eastern Kentucky through the end of the TAF period. These clouds are associated with both a departed area of low pressure aloft and a second upper level system that will approach from the southwest this evening and tonight. MVFR CIGS are expected through between 5 and 7Z tonight. After that, much lower clouds are forecast to move in, with IFR TO LIFR CIGS of around 500 feet expected. The first rain showers should begin moving across the TN border into eastern KY between 1 and 2Z this evening, with the rain becoming widespread by between 6 and 8Z area wide. SME and LOZ can expect rain to affect their sites around 5Z, JKL by 6Z and SYM and SJS between 8 and 9Z. IFR to MVFR VSBYs will be possible with any rain showers, with the lower VSBY associated with the more intense rain showers we will experience late tonight.These low CIGS are expected to persist through the end of the TAF period once they set in. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...AR SHORT TERM...JMW LONG TERM...RAY AVIATION...AR

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