Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 171120
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
620 AM EST Sun Dec 17 2017

.SHORT TERM...(Today through Monday)
Issued at 421 AM EST SUN DEC 17 2017

The morning surface analysis shows an area of high pressure
remains off to the southeast and we remain in control of this
feature this morning. The feature of interest for the near term
period will be a upper level closed low that is located across
Kansas with the axis extending into the Arklatex this morning.
The model soundings and time height analysis show a thick layer of
drier air near the surface and this will be difficult to overcome
today. There is a window this afternoon when we see the potential
for deeper layer moisture connection. The other issue is the
models have been in good agreement on the upper level shortwave
dampening as it moves northeastward into the Ohio and Tennessee
Valleys, and the weak low level jet remaining further south of the
area. Given this and the fact that the guidance came in lower did
lean toward lower POPs overall for today, with best chances
residing in the Lake Cumberland region. Right now will lean closer
to the better lift time for the better POPs and will continue to
monitor radar trends for subsequent updates for POP timing.
Overall for today with cloud cover and rainfall potential kept
afternoon highs in the mid to upper 40s.

This system will progresses east and flattens out as mentioned
above for tonight. The caveat will be low level inversion will
trap moisture near the surface and leave the potential for
lingering stratus deck tonight. The models have also painted
sporadic instances of omega and QPF at times and this will likely
translate to patchy drizzle at times tonight. The temperatures
tonight will remain uniform and generally in the mid to upper 30s
given the lack of airmass change and cloud cover. Given the
aforementioned persistent inversion and low level moisture did
lean toward higher cloud coverage for Monday. Also a strengthening
jet aloft could provide continuing support for patchy drizzle
through the day on Monday and added this to the grids. The biggest
caveat in this period will be the fact that the inversion is not
as strong and this could put us at jeopardy for mixing out the
inversion. For now, thinking this will remain in place and provide
the platform for cooler temperatures than painted by the model
blends. Therefore will lean toward afternoon highs topping out in
the upper 40s to lower 50s.

.LONG TERM...(Monday night through Saturday)
Issued at 442 AM EST SUN DEC 17 2017

The models are in good agreement with a split-flow long wave pattern
to start out across the CONUS into the middle of next week, with
the Ohio and Tennessee valleys seeing more influence from the
southern stream. The long wave pattern will then amplify
significantly towards the weekend, with phasing taking place and
a deep trough evolving across the center of the CONUS, bringing
increasing confidence that colder air will eventually affect much
of the lower 48 closer to Christmas. Details on the evolution of
this trough and surface features continue to be lower confidence
at this point, and will continue to rely on a blend of the
guidance in order to mitigate model inconsistencies this far out.

Skies look to be mostly cloudy across eastern Kentucky through
Wednesday. Initially, we hang onto low clouds trapped under an
inversion into Tuesday. A short wave trough will also move from
the Desert Southwest to the Tennessee Valley through Wednesday,
bringing reinforcing cloud cover as well as a decent chance of
precipitation, mainly south of the Hal Rogers Parkway and Highway
80 corridors.

Dry weather will return for Thursday, before a more significant
cold front takes aim at the area Friday into Saturday. POP chances
have increased for this time frame, peaking in the likely range
by Friday night. Most of this precipitation looks to fall as rain;
however, there is still some snow potential late Friday night
into Saturday morning, as colder air races against the exit of the
deeper moisture.

Overall, temperatures through Saturday will average above normal,
with colder air waiting to move in just beyond the forecast
period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 620 AM EST SUN DEC 17 2017

The period is beginning with high clouds and VFR conditions
across eastern Kentucky. We continue to watch a upper level system
approach from the southwest and this will bring an area of
rainfall toward the region. WE are drier in the lower levels early
and this will initially mitigate precipitation from making it to
the ground. We will see best chances of precipitation and lowering
CIGS to MVFR this afternoon. Then lingering low level moisture in
the form of stratus deck will remain in place and descend through
the TAF period. This will lead to the potential for drizzle and
IFR or lower CIGs to round out the TAF period. The winds will
remain light out of the south and southwest.

&&

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

$$

SHORT TERM...DJ
LONG TERM...GEOGERIAN
AVIATION...DJ


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