Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 162359 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
659 PM EST Thu Nov 16 2017

.UPDATE...
Issued at 659 PM EST THU NOV 16 2017

The latest satellite trends reveal lower clouds in the north
holding in place, with even a bit more push to the south southwest
out of West Virginia, as the low level flow remains north
northeast. Subsidence, associated with some height rises into the
overnight will likely keep the deck from advancing too much
further south, similar to what happened earlier in the day.
Forecast lows look on track thus far, and will reassess the
numbers more closely later this evening. Did adjust the diurnal
curve a bit in the north, allowing for a slower drop off given the
cloud cover. Updates will be out shortly.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 234 PM EST THU NOV 16 2017

The low cloud deck over the northern part of the forecast area
made an advance south early today, but the southern edge of the
clouds eroded at the same time. The erosion of cloud on the
southern edge of the cloud deck seems to be winning out slowly but
surely. As surface high pressure and some weak ridging aloft
builds into the area tonight, expect mostly clear skies to end up
being the rule across the entire forecast area. Clouds have held
temperatures in the upper 30s in the far north today, with
temperatures rising into the upper 50s in the south. With
clearing expect all areas to fall to near or below freezing
tonight. Any fog tonight will be limited to a few valley
locations mainly near water sources.

On Friday temperatures will warm as surface high pressure shifts
east and winds take on a southerly component. With plenty of
sunshine temperatures will warm to the mid 50s in the north to
the lower 60s in the south.

Sheltered valleys should decouple Friday night, allowing a minimal
ridge valley temperature difference to develop, especially early
and mainly in the east. However as cloud cover increases valley
temperatures will rise late in the night. A warm front will also
lift into the area Friday night in advance of low pressure moving
from the central plains to the mid MS valley. With some lift and
increasing moisture, showers will become possible across the
northwest half of the forecast area by late Friday night.

.LONG TERM...(Saturday through Thursday)
Issued at 349 PM EST THU NOV 16 2017

Model solutions are in good agreement through much of the extended
diverging more significantly by DY6, Tuesday. Main feature of
interest in the long term is a large trough that swings across
the eastern CONUS and through the Ohio Valley Saturday into
Sunday. Main trough axis is through the Commonwealth by Sunday
morning. However, models do hint at some lingering shortwave
energy rounding the base of the parent trough Sunday which may
help keep some shower activity going in the east Sunday morning.
Thereafter the pattern aloft may transition into a bit of a split
flow regime as energy digs into the deep south. But details are
difficult at best to iron out until models come into better
agreement. For now will stay with the blended solutions and
model guidance for the remainder of the period.

This main system of interest is quite strong and forcing is
better than usual with the H850 trough almost aligned (nearly
stacked) with the surface front as it passes through our area.
Consequently there should be some fairly rapid and strong
subsidence behind this system as it exits to the east. Included a
mention of isolated thunder for Saturday afternoon and early
evening. Instability is very marginal. But thunder can not be
totally ruled out and it provides for a better collaborated
forecast with neighbors. Winds on Saturday will be the main focus
with respect to hazardous weather. Gradient south winds will
increase through the day and become gusty. Wind flow aloft will
increase to between 35 and 65 kts. With any sunshine and good
mixing, and/or any strong showers and thunderstorms, there is the
potential to mix down some of those higher winds. For now will
maintain inherited gust potentials of up to 40 mph and continue
the process of increasing awareness of the wind hazard.

Nothing much to add beyond early next week except to say that
differences in model solutions show up very well in guidance. In
general our weather appears more dry than not. But trends in other
elements of sensible weather are very difficult to pin down. For
example, 12Z GFS MOS guidance is some 15 to 20 degrees cooler on
Thanksgiving than the ECMWF. Take your pick, mid 60s with the
ECMWF or mid 40s with the GFS. In the end reality typically winds
up being closer to somewhere in the middle that far out in the
forecast. ATTM that`s where we will leave the forecast. But it
does make for an interesting wait and see moment.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 659 PM EST THU NOV 16 2017

Low level clouds will continue to plague SYM through at least 06z.
These will invade into SJS between 02 and 06z. Thereafter, the
clouds should gradually scatter out. Some patchy IFR or worse fog
may form late, but this should be confined to the deeper river
valleys. Once the fog burns off, VFR conditions will prevail
through the rest of the period. North winds at 5 to 8 kts, will
gradually veer to the east and eventually southeast through
Friday.


&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...SBH
LONG TERM...RAY
AVIATION...GEOGERIAN



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