Area Forecast Discussion
Issued by NWS Jackson, KY

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275
FXUS63 KJKL 182340
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
640 PM EST Wed Jan 18 2017

.UPDATE...
Issued at 640 PM EST WED JAN 18 2017

Surface analysis shows high pressure is cresting across central
KY and will continue to move east. The challenge tonight will be
with far eastern stratus deck and the implications of this
temperatures/fog production. That said the stratus deck has hit
the breaks and updated sky grids to better deal with this. Right
now only high clouds are moving into areas south of the stratus
and would suspect these areas to drop off temperature wise quicker
than the far eastern typically colder valley sites. Therefore
will have to keep an eye on this and update as needed to deal
with latest obs and trends.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 415 PM EST WED JAN 18 2017

As of mid afternoon, an upper level ridge extended from the
Caribbean northwest into the Lower OH Valley and Mid Ms Valley
region. Meanwhile a broad upper level low extended from the
Central Plains to the Southern Rockies. Meanwhile, surface high
pressure was centered over the Lower OH Valley while low pressure
was starting to organize over the East TX/Arklatex region. A
stationary front extended northeast and then east from this
developing system across the Southeastern States.

Tonight, the axis of the upper ridge should gradually move east
and be over the region by dawn on Thursday. Meanwhile, the upper
level low will meander across the Central and Southern Plains
Region. Surface low pressure should continue to organize and reach
southern AR late with the boundary to the east lifting north as a
warm front and into southern TN. The upper level low should
meander toward slowly east and northeast toward the MS Valley on
Thursday into Thursday night and gradually weaken. The surface low
should track northeast during that time as well and reach IL by
the end of the period. During the same time, the warm front should
begin to lift into the area.

Clouds should continue to erode to the north and east through the
evening as mid level heights rise. This clearing or partial
clearing and the surface high building into the area should lead
to valleys decoupling and some valley fog is anticipated to
develop due to the lingering low level moisture. Mid and high
clouds will also begin to thicken and lower late tonight and into
the day on Thursday. However, these will reach the northern and
eastern locations last so those valleys should be the coldest and
have not that far to fall from current readings to approach the
freezing mark.

The warm front and upper level system will begin to approach the
area on Thursday as the upper level ridge axis moves east.
Moisture will increase from the top down through the day and
thickening and lowering clouds are expected from southwest to
northeast and rain showers should move in from the TN Valley and
encroach on the Lake Cumberland Region by early to mid afternoon.
The precipitation should gradually spread north and east through
late afternoon, but the low level flow will have a downslope
component and this should slow down the progression into the
southeastern counties and lead to lower initial QPF there as
well. Temperatures should moderate again to the 15 to 20 degree
above normal range for this time of year.

As the warm front and shortwave trough approaches the area on
Thursday evening and Thursday night and even takes on a bit of a
negative tilt, an area of showers should move across the area on
Thursday night and appears to peak between about midnight and 4 AM
on Thursday when best combination of lift and moisture should be
over the region. Some limited elevated instability is also
expected to be present at that point so isolated thunder will also
be a possibility during that time. Categorical pops look to be in
order given the projected moisture and lift and statistical MOS
guidance also in the categorical range. Rainfall from this system
should generally be moderate, though some heavier amounts will be
possible across the southwest where 12 to 18 hour amounts could
near an inch.

.LONG TERM...(Friday through Wednesday)
Issued at 337 PM EST WED JAN 18 2017

The extended forecast period begins on Friday with an active and
progressive pattern in place. A short wave will track northeast
through the Midwest and Middle Atlantic states on Friday. The
general progression of this feature seems to push through rather
quickly and the Euro and GFS agree on this. Precip will be brief
as it will exit the area by Friday night. In this active pattern
and on the heels of Fridays system another wave develops in the
lower MS River Valley and tracks northeast into the central
Appalachians by Saturday afternoon bringing another shot of
rainfall to the area. Isentropic ascent with this next feature
will pose the possibility for thunder but being well capped at
onset will hinder this possibility so will leave out of the
forecast for now.

The active pattern continues into the beginning of next week as a
secondary upper low dives into the lower MS Valley and lifts
northeast again through the area late Sunday and into Monday. This
shot of rainfall will appear to be the most out of the series as
the GFS and Euro agree with up to an additional 3 quarters of an
inch QPF expected in far eastern Kentucky by Tuesday. Most of this
rainfall appears to fall in the headwaters of Eastern Kentucky.
Total rainfall for this period looks to be up to 2 inches over a
48 hour period. At this time, its nothing to be too concerned
about with rainfall but will put a mention in the HWO.

Through the extended forecast, the warm trend continues with
temperatures in some days nearly 20 degrees above normal. So, will
not expect any frozen precip through the extended.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 622 PM EST WED JAN 18 2017

MVFR deck remains a issue to start the TAF period for SYM/JKL/SJS,
but improvements to high clouds have been seen in the Lake
Cumberland region sites. The breaks have really come on with
regards to the low clouds and tried to indicate this in the sky
grid and CIGs. Right now not confident how much if any clearing
will be seen across the far east, as some guidance suggests
lowering of the cloud deck or possibly fog. Right now confined
fog to SJS/SYM/SME and keep other sites VFR through the period. A
warm front is still expected to move north and precip will creep
back into the region to round out the TAF period. That said, for
now bring best chance of showers at LOZ/SME by later tomorrow
afternoon. Winds will will remain light through the period and
become more southeasterly by tomorrow.

&&

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

$$

UPDATE...DJ
SHORT TERM...JP
LONG TERM...SHALLENBERGER
AVIATION...DJ



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