Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 270536

National Weather Service Jackson KY
136 AM EDT Tue Sep 27 2016

Issued at 136 AM EDT TUE SEP 27 2016

Decreased the sky cover across much of the area per recent IR
imagery trends. Also freshened up the hourly temps and sent
updates to NDFD and web servers.

UPDATE Issued at 757 PM EDT MON SEP 26 2016

Outside of a rogue sprinkle in the higher terrain, rainfall has
come to an end across eastern Kentucky. Drier air will continue to
filter east behind the cold front, now positioned on roughly a
Pittsburgh to Charleston to Bristol line. Cloud cover will
decrease and lift through the evening into tonight, setting the
stage for at least some patchy fog development in river valleys.
Areas that saw rain Monday afternoon, mainly across the Bluegrass
region and along the Virginia/West Virginia borders, will also
stand a decent shot at seeing some lowering visibilities by
Tuesday morning. Timing of the impending clearing and strength of
the dry air advection will have to be monitored in regard to how
widespread/dense any fog will become.


.SHORT TERM...(This evening through Tuesday night)
Issued at 327 PM EDT MON SEP 26 2016

A cold front is currently moving across eastern KY as of 3pm today.
While the initial line of showers and thunderstorms has sheared out
along the weakening frontal boundary during its eastward
progression, warm air and clear initial conditions across far
eastern KY helped to increase instability across this area during
the early afternoon. A gust front which pushed out well ahead of the
initial line then became the spawning ground for another line of
showers and thunderstorms across far eastern KY. For the rest of the
afternoon, expect the showers along the frontal zone to continue to
shear out and breakup. Meanwhile the secondary and more robust line
of showers and thunderstorms will continue to slowly move east of
the state. Also cannot rule out some isolated to scattered
convection between the two lines for the next few hours as well.

Since NW flow began ahead of the actual cold front, and cloud cover
is in place, expect cooler temperatures to continue to penetrate the
CWA through the rest of the afternoon. This will only work to weaken
any convection potential. The 850 mb frontal passage will
traverse the CWA later this evening and into the overnight, generally
after 0z. It is at this point that we will really start to tap into
the much cooler airmass to our NE. Strong NW to SE upper level flow
will feed Canadian air into the region throughout the remainder of
the short term thanks to a strong upper level closed low circulating
to our north. Low temperatures tonight will fall into the upper 40s
to low 50s once we begin clearing out behind the frontal passage.
Temperatures tomorrow will finally feel more seasonable, if not a
couple degrees below, topping out in the low to mid 70s with surface
high pressure in control. Clear conditions will continue Tuesday
night with temps expected to fall back into the 40s with light
southerly winds.

.LONG TERM...(Wednesday through Monday)
Issued at 302 PM EDT MON SEP 26 2016

Models continue to come into better agreement concerning a large
upper low to affect the eastern CONUS early in the period. The ECMWF
has been the most consistent in handling the system over the last
few days. A model blend will be used to account for remaining
differences. The upper low will be slowly dropping south from the
Great Lakes on Wednesday, and should bottom out over KY on Thursday.
Even with a cool surface air mass in place, cold air aloft should
result in lapse rates steep enough for showers and possibly even
some thunderstorms to occur. Precip timing and location will depend
partly on small scale features rotating around the large system,
with timing also being linked with diurnal destabilization. Model
handling of small scale features will go through changes yet, which
puts a limit on forecast confidence. Will not use any pops above
chance category at this point, but that could change in later
forecasts. Diurnal trends are more predictable and will be

The low should lift back north over the weekend, taking precip with
it. Low level warm air advection is expected to be slow to return,
but additional sunshine and mixing, and warming temps aloft will
allow for a slow warming trend.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)

Main concern during the early morning period is the potential for
fog development. Current thinking is that SME will be the main TAF
site to be affected due to earlier clearing and temperatures
already at saturation. Some fog is already being seen in the IR
fog channel just south of our border in TN and expect this to
spread northward as the clouds continue to push off to the east.
That being said, have introduced MVFR fog at SME but kept VFR fog
at LOZ and JKL through dawn. There is the potential for lower VIS
across the area but confidence remains marginal at this time. The
fog should lift by 13-14Z this morning and VFR conditions will
prevail with mainly clear skies. Winds will be light and variable
around 5 knots or less through the period.




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