Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 251213 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 713 AM EST Sat Feb 25 2017 .UPDATE...
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Issued at 705 AM EST SAT FEB 25 2017 The deeper moisture has just about exited far southeastern KY and pops have been adjusted early in the period to account for this. A dry slot will work across the area early in the period, though shallow low level moisture will return by late morning to early afternoon as the shortwave trough approaches and a return or continuation of stratocu and cumulus is expected. The low level flow will have an upslope component and the shallow moisture is expected to be near the -10C level. This may be sufficient for a few sprinkles or perhaps an isolated light shower by midday to the afternoon as lapse rates steepen. A few flurries cannot be completely ruled out by evening. However, drier air moving in as high pressure builds into the TN Valley should put an end to the threat for sprinkles or flurries during the evening. Temperatures are expected to be nearly steady or slowly falling in the morning with a more substantial fall in the afternoon as the core of the cold airmass nears.
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&& .SHORT TERM...(Today through Sunday) Issued at 425 AM EST SAT FEB 25 2017 A cold front associated with a deep low pressure system moving from the Great Lakes and into Ontario is currently moving across East KY. The boundary is currently located from between KHTS and KCRW south southwest to just west of KSJS and KPBX to near K1A6 and then to near KTYS and KCHA. An area of showers associated with the front and associated mid and upper level trough and forcing along with some embedded thunderstorms are moving across the area. However, these are slowly tapering off from west to east with the thunder generally confined to areas near or east of the front from portions of the Big Sandy region southwest near the VA border. Temperatures have initially web bulbed with the precipitation into the 50s while colder and drier air is filtering into the area behind the front and temperatures and dewpoints in the west have dropped into the 40S. As the front moves into VA over the next hour or so, the threat for any lingering thunder will end although some showers will persist for a couple of hours or so behind the front until the deeper moisture departs and forcing decreases. Cold air advection will continue today as the mid and upper level trough axis approaches with the coldest of the airmass arriving this afternoon and evening. 850mb temperatures should fall below 0C by midday and bottom out near -10C late this evening into very early on Sunday. At the surface, high pressure will build east from the Plains and this combination should bring steady to slowly falling temperatures through the morning and gradually falling temperatures in the afternoon. The highest elevations above 2500 feet should drop to around freezing or below by sunset while the remainder of the area should fall below 40 by dark. There should be a period of relatively less cloud cover in the morning as a dry slot between the front and upper level trough moves across the area. Limited low level moisture will linger with cu and or stratocu developing or increasing from midday into the afternoon as the cold advection steepens lapse rates. This moisture may be sufficient with some ice present in the clouds for a few sprinkles by this afternoon and perhaps a few flurries in some areas toward sunset, particularly the highest elevations. As the high builds east this evening and tonight and is centered over the TN Valley, the pressure gradient will decrease as will low level moisture. This should occur first across the southwest part of the area and a bit later in the northeast. This pattern will favor a bit colder low temperatures in the lower 20s for some normally colder southern valley locations though all locations should fall into the 20s. The high will begin to move east of the area on Sunday and with a considerable amount of sunshine, high temperatures should rise to near normal levels for the end of February as the airmass moderates rather quickly. The airmass will also be dry and rh should bottom out briefly below 30 percent in some locations. .LONG TERM...(Sunday through Friday) Issued at 315 PM EST FRI FEB 24 2017 The extended portion of the forecast will be fairly active, with alternating periods of wet and dry weather and warm and cooler conditions. The period will likely start off dry, with slightly above normal temperatures Sunday and Sunday night. The pattern is then expected to shift on Monday, as a weak warm front moves through the area, bringing persistent southerly flow and warmer air into the region. Rain showers should begin to move into the area from the southwest and west late Sunday night into early Monday morning. The rain will overspread the entire area by late Monday afternoon and early Monday evening, as an area of low pressure moves along what will become a nearly stalled out frontal boundary. This pattern is tentatively expected to persist through late in the day on Tuesday. A wave of low pressure is then forecast to form along the western end of the stalled front Tuesday night. This second area of low pressure is then expected to push eastward on Wednesday, and will drag another cold front across the lower Ohio valley and Tennessee valley regions. This boundary may be just strong enough, and just enough moisture an instability available, for a few thunderstorms to form along and just ahead of the front, as it moves across the region. Once the front moves past us Wednesday night, any thunderstorms should give way to all rain showers. We may even see enough cold air filter in behind the system to allow some snow to mix in with whatever rain is left. The last of this precipitation should be out of the area by late Thursday morning. Thursday and Thursday night should be mostly dry. There is an outside chance that a few rain and snow showers will move across the area along and north of I64 to end the period, with due to uncertainty, this should be taken with a grain of salt. Temperatures in the extended on average will be above average each day, with the warmest days being Monday, Tuesday, and Wednesday, when the highs will be in the 50s and 60s. Closer to normal values should be experienced on Thursday, when the mercury is forecast to max out lower 50s. Nightly lows should be in 30s, 40s, and 50s. && .AVIATION...
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(For the 12Z TAFS through 12Z Sunday morning) ISSUED AT 710 AM EST SAT FEB 25 2017 Initial lower end of VFR and MVFR Cigs are expected to start the period though as drier air moves into the area combined with mixing by the 14Z to 18Z period, all locations are expected to become VFR. A few sprinkles and perhaps a flurry cannot be ruled out through 23Z. Winds should increase by 16Z with daytime heating with generally west winds 10 to 15KT with some gusts as high as 20 to 25 mph. The pressure gradient will slacken by 0Z to 6Z with winds becoming light at the end of the period.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...JP LONG TERM...AR AVIATION...JP

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