Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 150612 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
212 AM EDT Sun Oct 15 2017

.UPDATE...
Issued at 155 AM EDT SUN OCT 15 2017

Hourly grids were freshened up based on recent observations and
trends. This led to no substantial changes at this time. Valley
temperatures appear to be leveling off so the previous forecast of
a slight rise in temperatures for valleys late tonight appears on
track as winds likely begin to mix into the valleys ahead of an
approaching front. A few low clouds have developed near terrain
features in the Cumberland Plateau and in the Cumberland
Mountains near the VA/TN/KY border area and model guidance
suggests these could increase in coverage overnight, but
confidence on this remains low.

UPDATE Issued at 1004 PM EDT SAT OCT 14 2017

Main concerns for the update are temperatures and fog tonight. The
normally colder valleys in the eastern portion of the area were
already reaching previously forecast lows at 9 pm. Saturation was
already occurring in those locations. That being the case, min
temps in most valleys were lowered, and patchy valley fog was
added to the forecast. The big question comes overnight as winds
just off the surface pick due to warm air advection ahead of the
approaching cold front. Suspect it will be enough to cause the
valleys to begin to mix again, and hence, warm up and lose the
fog. However, exactly when/where that occurs is uncertain, and
it will determine how cold it gets first. In terms of
temperatures and fog in valleys overnight, it`s a fairly low
confidence forecast.

UPDATE Issued at 409 PM EDT SAT OCT 14 2017

Have added a minimal 20% POP in a small portion of the southwest
corner of the forecast area through early evening. Radar shows
that shallow convection there is producing some spotty light
precip. The convection weak and is capped pretty low, and should
die out with loss of heating this evening.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 303 PM EDT SAT OCT 14 2017

The focus of the short term is the cold front that will move
across the area on Sunday. There is good model agreement that the
front will be southeast of the area by 00Z Monday. The best
forcing will remain well to the northeast of the area on Sunday,
and instability still looks to be very limited. Thunder potential
remains very low, but considering we are in the SPC general
thunder outlook area for day 2, and that we`ve been carrying a
slight chance of thunder for Sunday for several days, we will
continue with a slight chance of thunder for Sunday afternoon. We
will also go with categorical rain chances, but the QPF will
remain light, generally 0.25 inch or less. One thing of note for
Sunday is the southwest winds ahead of the front which will
increase significantly Sunday morning, with some gusts in excess
of 30 mph possible mainly in the western part of the forecast
area. Cooler air will begin spreading into the area Sunday night
with temperatures falling into the 40s.

.LONG TERM...(Monday through Saturday)
Issued at 215 PM EDT SAT OCT 14 2017

The models are in fairly good agreement with the mid level longwave
pattern through the extended portion of the forecast. They all
depict a well clustered trough departing the Great Lakes and Ohio
Valley early on in the new week. Heights will rebound in the wake of
this trough, though not dramatically. As a result, some weakness
with temporally increasing model spread will pass through Kentucky
from Tuesday night through Wednesday in the form of a dampening
shortwave. After this marginal feature moves on past, heights will
resume their climb building quickly over the Tennessee Valley and up
into the Ohio Valley to end the work week. Model agreement here is
quite good and remains that way into the weekend with the ridge
dominating over eastern Kentucky - in the more reliable GFS and
ECMWF. Given the solid model consensus through the bulk of the
extended am not looking to make any wholesale changes to the blended
starting point.

Sensible weather will feature another extended period of dry
weather with good warming taking place through the latter portion
of the week and into next weekend. High pressure of moderate
strength will hold court over the eastern portion of the nation
through at least the work week. This air mass will start out
chilly in the aftermath of a cold front passing through by Sunday
evening. In fact, we will need to be on the lookout for some
patchy frost in the deeper valleys Tuesday morning. However, the
air will moderate quickly particularly later in the period. The
weakness in the pattern aloft around Tuesday/Wednesday will have
little reflection at the sfc or in the sensible weather given dry
low levels. Do expect at least patchy fog around each morning
given the time of year and adequate boundary layer moisture left
over from the rains of Sunday`s cold front. Also anticipate decent
ridge to valley temperature splits through the extended - more
prominent for the latter half than at the beginning when the high
will still be building into the area. Rain chances look minimal
throughout the extended forecast. Some record high temperatures
will be possible by the weekend thanks to ridging aloft,
additional drying, and an increasingly stagnant area of sfc high
pressure.

Through the forecast made the typical terrain based adjustments to
the grids most nights, aside from Monday in the immediate wake of
the front. As for PoPs, basically removed them from the forecast
given the good consensus for this upcoming dry period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday evening)
ISSUED AT 205 AM EDT SUN OCT 15 2017

Skies have cleared and VFR conditions prevailed across the area at
the start of the period. The areal extent of fog is much more
limited compared to 24 hours ago and it is not expected to affect
the TAF sites. VFR should continue through most if not all of the
night across a majority of the area. 0Z models continue to
indicate the potential for low clouds to develop, especially in
the south although the extent and timing remain uncertain as these
so far have been only affecting the Cumberland Mountains near the
KY/TN/VA border area. By mid day, all but the far eastern portion
of forecast area will likely have VFR or MVFR ceilings as a cold
front moves in from the northwest. Showers are forecast to
overspread the area from northwest to southeast generally after
16Z, with a few thunderstorms also possible. MVFR and possible
brief IFR reductions are expected with these. Winds will pick up
to 10 to 15KT from the southwest during the day, with some gusts
topping 20 kts. A shift in winds to the west northwest will occur
after 20Z as the front passes.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...JP
SHORT TERM...SBH
LONG TERM...GREIF
AVIATION...HAL/JP



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