Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 181205 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 805 AM EDT Fri Aug 18 2017 .UPDATE...
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Issued at 745 AM EDT FRI AUG 18 2017 Did a quick update to fine tune the PoPs and Wx grids through Noon and also to adjust the T/Td grids per the latest obs and trends. These have been sent to the NDFD and web servers.
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&& .SHORT TERM...(Today through Saturday) Issued at 400 AM EDT FRI AUG 18 2017 07z sfc analysis shows a broad and fairly deep area of low pressure over the Great Lakes with a cold front stretching south and southwest through the Ohio Valley. This front is just west of the JKL CWA and pressing eastward with clusters of showers and embedded thunderstorms out ahead of it. A few of these clusters are exhibiting training and will have to be monitored for excessive rains through the next few hours. Clouds have overspread most of the CWA early this morning ahead of the boundary and with the convection, though some clear patches are found in the far east where the best shot at seeing some fleeting, but locally dense, fog exists. Temperatures are running in the very mild low 70s most places with dewpoints equally high. A few of the convective cells have also been able to bring down some higher wind gusts - up to 30 mph from the southwest, otherwise winds are generally light and from the south throughout eastern Kentucky early this morning. The models are in good agreement aloft building a trough over the region through the short term portion of the forecast. They all depict a decent short wave passing through the northern parts of the area this morning as height falls spread through Kentucky. The troughiness over the region will be reinforced on Saturday as a substantial wave moves across the Ohio Valley with further height falls as the main trough bottoms out. This features moves by quickly, though, with heights starting to rebound by evening. Given the good model agreement have favored a general blend with greatest consideration to the radar trends and higher resolution HRRR in the near term - NAM12 thereafter. Sensible weather will feature showers and potential thunderstorms passing through the CWA for the first part of the morning with much of this taking place in the pre-first period time frame - so will run the ZFP formatter with that in mind. Drier air and clearing skies then move into the region this afternoon with not so high dewpoints on tap. As the air mass changes today, a cooler but still mild, night will ensue but cold to neutral advection will limit terrain differences, though some valley fog can be anticipated under a regime of mostly clear skies and light winds. For Saturday, slightly more comfortable humidity levels will not prevent temperatures from climbing into the seasonable norms of mid 80s for highs under partly sunny skies. Given the trough push aloft, though, cannot rule out a stray shower or storm, mainly in the far north during the day, but limited moisture availability should make this a minor concern. Once again the CONSShort was used as the starting point for the grids through the short term portion of the forecast with only small adjustments to temperatures for terrain distinctions. As for PoPs, mainly adjusted them up this morning given the ongoing radar trends and beefy HRRR through dawn. Also trimmed them back quicker than guidance later this morning. .LONG TERM...(Saturday night through Thursday) Issued at 445 AM EDT FRI AUG 18 2017 The axis of a shortwave trough will be exiting to our east to start the extended portion of the forecast, with rising heights expected through the day Monday as a high pressure ridge establishes itself along the far southeast. Heights will quickly lower, however, as a upper level low dive bombs to the SE through eastern Canada Tuesday, continuing across Ontario and then Quebec Wednesday. A secondary low will develop and strengthen the longwave trough across the eastern U.S. to finish out the forecast period. As for sensible weather... High pressure will be in control at the surface to start the first part of the forecast period, being reinforced by the upper level ridge. This will boost temps above normal in the upper 80s both Sunday and Monday. There was some discrepancy about a few afternoon diurnal showers/thunderstorms in the CWA Monday. However, latest models are continuing to go more dry. The GFS does put a spot or two over us in the afternoon in the high terrain, misplaced from the previous run. Given its weak and isolated nature, and the inconsistencies between model runs, capped pops at 14 so that no mention of precip was in the forecast. As the ridge breaks down aloft, a surface low is expected to move eastward north of the state. From this a cold front will sink southward, traversing Kentucky through the day Wednesday. This will bring chances for showers and thunderstorms to the region as early as during the day Tuesday, increasing to likely coverage during the day Wednesday just ahead of the frontal passage. Chance of precip will remain in place Wednesday night, tapering off from north to south during the day Thursday. Given the lack of post frontal instability, kept only rain mentioned from Wednesday night on. Temperatures will remain in the upper 80s during the day Tuesday as warm moist air is advected in ahead of the frontal passage. However the trend thereafter will be a cooling one. Wednesday will see highs in the low 80s, Thursday right upper 70s to right around 80, and by Friday, only mid and upper 70s. Overnight temperatures will be much cooler during the last part of the work week as well. && .AVIATION...
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(For the 12Z TAFS through 12Z Saturday morning) ISSUED AT 755 AM EDT FRI AUG 18 2017 The main cluster of showers and a few embedded thunderstorms is pushing through far eastern parts of the CWA this morning with some IFR conditions. Following the departure of the convection conditions will improve at all TAF sites with VFR returning. Winds, outside of any storm, will be light and variable through mid morning before picking up from the west at 5 to 10 kts post fropa.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...GREIF LONG TERM...JMW AVIATION...GREIF is the U.S. government's official web portal to all federal, state and local government web resources and services.