Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 170800
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
300 AM EST Fri Nov 17 2017

.SHORT TERM...(Today through Saturday)
Issued at 300 AM EST FRI NOV 17 2017

07z sfc analysis shows high pressure centered just northeast of
Kentucky with its influence noted in the cold temps and light
northeast winds at the sfc. However, it is not enough to clear out
the low clouds stuck over the CWA and is likely helping to keep
them trapped. As such, the temperatures are fairly uniform across
eastern Kentucky in the low to mid 30s. Dewpoints, meanwhile, vary
from the upper 20s north to the mid 30s in the far southwest parts
of the area. Also, thanks to the clouds, fog has been kept to a
minimum.

The models have come into good agreement aloft with the pattern
affecting the region through the short term. They all depict
benign northwest flow over Kentucky today becoming more
southwesterly tonight as energy from a sharp and deepening western
trough spreads quickly into the region and over the state. This
will continue to be the case into the day Saturday as the
progressive trough digs into the Mid Mississippi Valley looking to
punch into the Ohio and Tennessee Valleys Saturday evening and
overnight. Much better agreement exists among the models with this
develop now than the past several runs and confidence is fairly
high in a blended solution for timing and placement of the key
forecast features. Even so, have favored the higher resolution
guidance from the HRRR and NAM12 for weather specifics through the
short term and in particular for Saturday.

Sensible weather will feature the low clouds breaking up quickly
just ahead of or following day break - generally from south to
north. Warming will then commence with temperatures climbing
smartly into the 50s and lower 60s mostly places under mostly
sunny skies. For tonight, the high pressure will have retreated
east in response to the approach of deep low pressure in the
Plains and eventually a potent cold front. This will present a
small window for radiational cooling for our valleys before
thickening and lowering clouds spread in from the west. Winds will
also likely kick up after midnight as the pressure field tightens
and a developing warm front lifts north of the state. Cannot rule
out a stray shower or two from this development tonight in the
northern parts of the CWA, but most places will stay dry. Look for
some limited instability to build over eastern Kentucky on
Saturday in the system`s warm sector with stray showers giving way
to a potential for thunderstorms in the afternoon. Some of these
could become quite strong given the dynamics aloft. Additionally,
winds will mix down from aloft particularly effectively with
gusts to 40 mph on tap owing to the path of the sfc and 850 mb low
center. The system`s cold front arrives around 00z with a
convective line of showers and embedded storms anticipated
dropping a solid half to 3/4 inch of rain and also helping to
bring down some of the stronger winds aloft to the sfc. Would
anticipate the need for a wind advisory for the entire area on
Saturday - through the evening. For now, though will continue to
highlight the threat in the HWO.

Used the CONSShort and ShortBlend as the starting point for all
the grids. Did make some adjustment to low temperatures tonight
for ridge to valley distinctions. Also, beefed up PoPs with the
fropa, anticipating that all places in the CWA will at least
measure, and lifted the thunder potential Saturday afternoon and
evening given the dynamics of the situation.

.LONG TERM...(Saturday night through Thursday)
Issued at 255 AM EST FRI NOV 17 2017

A strong cold front will be crossing the area at the start of the
period Saturday evening with strong dynamical forcing associated
with the feature thanks to a very strong 250mb jet. Very tight
pressure gradient with the front and we will likely see wind gusts
in the 30 to 40 mph range through at least 10 or 11 pm, before
winds start to taper off late. The NAM bufr momentum transfer
winds peaked right at 30 knots, which is typically the top end for
wind gust potential. We will likely need some kind of wind
headlines to go with this front, but way too early for those now.
There is also some potential for thunderstorms, although
instability is weak. However, the strong forcing alone warrants
the mention of thunder. In fact would not be surprised to see a
narrow line of intense showers/storms form right along the front
as it tracks across the area. Any organization of storms would
easily contribute to damaging wind potential, given the tremendous
shear in place. We will continue to highlight wind potential in
HWO and graphics.

Temperatures will turn sharply colder with the frontal
passage Saturday night, falling to around freezing in the highest
terrain in southeast Kentucky by midnight. Models in modest
agreement on some remaining moisture lingering through the night,
supporting a changeover to some snow across the high terrain. With
temperatures expected to reach the 20s on ridges above 3kft, some
snow accumulation seems likely. Model blend actually put about a
tenth of an inch of liquid on Black Mountain and this seems
reasonable given the upslope flow. This would amount to about an
inch of snow accumulation by Sunday morning. Temperatures at lower
elevations should stay at or above freezing preventing any snow
accumulations, although a few lower elevations could see a few
flakes very early Sunday. GFS ensemble members provide some
support to keep some snow/rain shower activity in the far east
into Sunday afternoon. Cloud cover was greatly increased through
Sunday given the trough hanging around. This cloud cover will keep
temperatures down as well, likely preventing them from getting out
of the 30s for most areas.

High pressure quickly builds in for Sunday night into early
Monday, setting the stage for the coldest night thus far for the
fall. Temperatures in the valleys could very well reach the teens
with low to mid 20s on the ridges. Temperatures will moderate as
we head into next week as heights begin to rebound. Dry weather
will likely persist as well with a mid level ridge crossing the
region through Tuesday. A moisture starved front will cross the
region on Wednesday and provide a cool down for the mid week
period, but temperatures will again warm as we head into and
through the holiday weekend. It looks like the weekend should at
least start off dry. Some uncertainly remains over the second
half of the holiday weekend that a system could impact the area
and bring some rain to the area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 1:10 AM EST FRI NOV 17 2017

Low stratus looks to plague eastern Kentucky for much of the night
with IFR and low MVRF cigs. Some clearing will likely start
working north as this cloud deck erodes toward dawn. Have timed
this through the rest of the night for the TAFs. Visibility issues
will be minimal due to these clouds, though, but deep valleys in
the far south could still see some restrictions. For Friday, any
lingering low cigs will quickly break up with sunshine returning.
Winds are generally northeast at around 5 kts and will stay that
way through the rest of the night. On Friday, as high pressure
moves farther off to the east winds will start to turn to the
southeast and south at 5 to 10 kts.

&&

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

$$

SHORT TERM...GREIF
LONG TERM...KAS
AVIATION...GREIF


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