Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 231144 AAB AFDJKL Area Forecast Discussion...UPDATED National Weather Service Jackson KY 744 AM EDT TUE AUG 23 2016 .UPDATE... Issued at 535 AM EDT TUE AUG 23 2016 Fog, locally dense in spots, has become more widespread across the southern and eastern counties over the past couple of hours. Expect this to continue through dawn as temperatures near their crossover values. In terms of the forecast, increased the fog in the grids to reflect current trends and freshened up the hourly temps. Sent updates to NDFD and web servers. && .SHORT TERM...(Today through Wednesday) Issued at 330 AM EDT TUE AUG 23 2016 Mid level dry air continues to push southward into Eastern Kentucky this morning, per latest WV imagery. This dry air has prevented fog development across the northern counties early this morning, with some dense fog present in the southern counties mainly near bodies of water. There is still potential more fog could develop close to dawn as temperatures near the cross-over temperatures. However, it won`t be nearly as widespread as the previous day. Any fog should being to lift around dawn and dissipate by 13Z. Surface high pressure will gradually slide off to the east later today but not before we have another beautiful summer day with lower humidities. As the high departs, southerly flow will set up and begin ushering in warmer and more humid air. This additional moisture will allow for some fog development tonight, mainly in the valleys and near bodies of water. A weak upper level shortwave will then cross through the forecast area Wednesday afternoon and interact with the unstable airmass. This interaction should be enough to spark isolated showers or thunderstorms during the afternoon and evening hours, even with mid and upper level ridging holding steady over the southeastern CONUS. The shortwave, and any shower activity, should exit the region by Wednesday night. .LONG TERM...(Wednesday night through Monday) Issued at 349 AM EDT TUE AUG 23 2016 The long term period is expected to begin with an upper level ridge of high pressure centered over the Southeastern States while a somewhat broad trough is expected to extend south through portions of the Rockies and Plains States from an upper low moving east near the US/Canadian border centered over southern Manitoba. Surface high pressure that has brought a reprieve from the humidity is expected be departing the Northeast at that point. Return flow between this high and a cold front advancing toward the Great Lakes and MS Valley ushering deeper moisture back into the Commonwealth. PW is projected to have increased into at least the 1.5 to 1.75 inch range by the start of the period. In addition, a few disturbances should also be moving around the ridge at that point. From Wednesday night into Friday, the upper low is expected to move into and across Ontario and Quebec and weaken to an open wave and approach the Canadian Maritimes by Friday evening. Meanwhile the associated surface low will also move east from Ontario and toward the Maritimes during the period. However, the ridging across the Southeast is expected to build north and east and be centered over the Central or Southern Appalachians by Friday evening. This will lead to the cold front becoming increasingly sheared with time and probably more diffuse as well as it drops south of the Ohio River. It should usher in a minimally drier airmass for the start of the weekend. During the period of increasing moisture from Wednesday night into Friday followed by the approach of the cold front convection will be possible. However, mid and upper level forcing should be minimal if not lacking much of the time. Thus only isolated to scattered pops continue to be forecast during the Wednesday night to Thursday period. Although nocturnal convection will be possible on Wednesday night as a weak disturbance passes, loss of daytime heating should lead to a dry or mostly dry period on Thursday night. Even with the front progged to move across the area on Friday the proximity of the center of the upper level ridge and or height rises should keep coverage mainly isolated. Upper 80s should be common for highs during this period with some of the warmer spots or more southern valley locations reaching or exceeding 90. Overnight lows will return to the upper 60s to lower 70s. Surface and upper level ridging should remain dominant over the weekend and into the start of next week. There remains uncertainty as to how close the center of the ridge will be to Eastern KY during this period. The past couple of ECMWF runs have higher heights from Friday evening into Saturday night, while the GFS and the previous ECMWF run have higher heights at the end of the period compared to the 0Z ECMWF run. The airmass should be moist enough for at least diurnally driven cumulus each day, with some of this possibly able to break the cap in a few locations each day. This would appear most likely over or near the higher terrain near the VA border to start the period. Then as the ridge possibly weakens or becomes centered further from the area, the cap possibly could be broken across more of the area on Monday. A warm and moist airmass will be across the region in any case with dewpoints expected to be in the upper 60s to lower 70s and 850 mb temps around 19C to 20C should keep temperatures in the upper 80s to around 90 for highs with overnight lows in the upper 60s to around 70 degree range. Heat indices should reach the 90s each day in many locations. && .AVIATION...
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(For the 12Z TAFS through 12Z Wednesday morning) ISSUED AT 744 AM EDT TUE AUG 23 2016 Areas of dense valley fog have led to variable conditions across the area this morning, with SJS dropping to MVFR at times. The fog should begin to dissipate around 13Z this morning. Once this occurs, VFR conditions will prevail for the remainder of the day as high pressure gradually slides off to the east. MVFR fog will be possible again late tonight at LOZ, SME, and SJS as return flow begins ushering in more humid air. Some non TAF sites will likely have some IFR vis in fog between 6Z and 12Z. Winds will generally be light and variable through the period.
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&& .JKL Watches/Warnings/Advisories... None. && $$ UPDATE...JVM SHORT TERM...JVM LONG TERM...JP AVIATION...JVM/JP

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