Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 061732 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1232 PM EST Tue Dec 6 2016 .UPDATE...
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Issued at 1232 PM EST TUE DEC 6 2016 An updated forecast has been issued. The primary change was to remove morning wording from the zone forecast text product. The grids were freshened up using the latest obs data, but no major changes were needed otherwise. We are still expecting widespread rain showers to move across the area over the next few hours before tapering off to scattered and eventually isolated showers. Patchy drizzle will be possible across the area as the rain showers become more isolated and the upper low creating all the rain moves off to our east. UPDATE Issued at 1010 AM EST TUE DEC 6 2016 The forecast remains on track so far today, with periods of widespread light to moderate rain showers expected across the area. Current temperatures should not change much during the course of the day, due to the ongoing precipitation and widespread cloud cover. Will not be updating the zone forecast text product just yet as the current forecast is good as is. An update will be required around noon today, to remove morning wording from the forecast text product and to make any other changes that may be necessary by then. UPDATE Issued at 728 AM EST TUE DEC 6 2016 Light to moderate rain continues across much of eastern KY, especially the southern half of the CWA. This seems to jive well with the ongoing POP and weather forecast. Still expecting rain to continue across the area throughout the day, so no updates needed to this portion of the forecast at this time. Temperatures will only increase by a few degrees throughout the day given the ongoing cloud cover and rain. Did update the forecasts for the near term temps, dew points, and winds, however, to make sure they were on track with current observations. All changes have been published and sent to NDFD/web.
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&& .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...
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(For the 18Z TAFS through 18Z Wednesday afternoon) ISSUED AT 1232 PM EST TUE DEC 6 2016 Complex TAF forecast today and tonight. Widespread rain showers will continue to move across eastern Kentucky through 21 or 22Z, before tapering off to scattered and then isolated showers between 23Z today and around 4Z tonight. Patchy drizzle will be possible behind the back edge of the rain showers this evening and tonight. Conditions at the TAF sites will vary from IFR to MVFR depending on the intensity of the rain. Widespread MVFR conditions are not expected to set in until after 5Z tonight. The clouds will be slow to exit the area, so BKN to OVC CIGS will be possible through around 13Z tomorrow. Winds will continue to shift from the southwest to northwest over the next several hours with sustained values at around 10 mph.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...AR SHORT TERM...JMW LONG TERM...GEOGERIAN AVIATION...AR

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