Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 281150 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
750 AM EDT Wed Oct 28 2020

.UPDATE...
Issued at 735 AM EDT WED OCT 28 2020

Did an update mainly to fine tune the near term PoPs and add in
the latest obs and trends for the T/Td grids. These updates have
been sent to the NDFD and web servers.

&&

.SHORT TERM...(Today through Thursday)
Issued at 505 AM EDT WED OCT 28 2020

08z sfc analysis shows a stalled frontal boundary lying across
far southeast Kentucky with high pressure well off to the
northwest. Plenty of clouds are found over the area this morning,
though there have been some thin patches and even some areas of
clearing north of the front resulting in river valley fog with
visibility likely fluctuating with the status of the clouds. We
are also seeing a decent ridge to valley split in spots out there
as readings are varying from the low 50s in sheltered valley and
northwest to the upper 50s and low 60s on some ridges and points
southeast. Meanwhile, dewpoints are generally a degree or two
lower than temperatures at each ob site with light and variable
winds.

The models are still coming into better agreement aloft through
the short term portion of the forecast. They all depict the
bowling ball closed low rolling across Texas today and tonight
while the upper levels of Hurricane Zeta lifts into the Deep
South. All this will continue to support rather fast southwest
flow over the state with energy from the upper low and Zeta making
it into our area tonight into the day Thursday. Given the
shrinking model spread for this dynamic pattern, will favor a
blended solution as represented by the NBM with some hedge toward
the deterministic models for PoP and timing details.

Sensible weather will feature wet conditions through the period as
twin weather makers converge over the region. The deep trough to
the west will push its sfc reflection storm toward the area at the
same time the remnants of Zeta ride through the eastern Tennessee
Valley. These systems will likely set up two main areas of heavy
rain - one to the northwest of the CWA associated with
frontogenesis and synoptic scale forcing while another shows up
in the Southern Appalachians more closely tied to the path of
Zeta`s remains. While all of eastern Kentucky faces the threat of
heavy rains, the plume analysis and deterministic QPF versus the
ensemble means suggest the main area of concern (and highest
forecast QPF) will be seen in the higher terrain of far southeast
Kentucky near the Virginia border. For this reason, and with
conjunction of MRX, have issued a Flash Flood Watch for our three
southern Virginia border counties running from 8 pm this evening
through 2 pm Thursday. Otherwise, look for times of fog through
the period with limited diurnal curves - though the northwest to
southeast variation in temps will remain.

Did not adjust the NBM temperatures all that much through the
period while preferring to blend its PoPs with higher values from
the deterministic models tonight through Thursday.

.LONG TERM...(Thursday night through Tuesday)
Issued at 605 AM EDT WED OCT 28 2020

October ends on a dry but chilly note and the first winter-like
air mass follows for the first of November. Model agreement is
good through the long-term. The latest model suite analysis,
beginning 0z Friday, shows the remnants of Zeta exiting off the
Atlantic Seaboard and strengthening into an early season snowstorm
for the northern Appalachians. This powerful system will be
supported by a a deepening trough passing through the Great Lakes/
Ohio Valley. At the surface, a double-barreled low, with one
center near the Delmarva Peninsula and a second center back over
the southern Appalachians, is trailed by a sharp cold front
extending from the central Appalachians SSE toward the Florida
Peninsula. To the west, a surface high pressure ridge extends
from northern Ontario to the Texas Plains.

The developing coastal storm and trailing cold front quickly
departs to to the east Thursday night-Friday morning while the
surface high builds in from the west. Initially, the northwest
post-frontal upslope flow, lingering low level moisture and
descending subsidence inversion aloft will keep eastern Kentucky
socked in under a low stratus deck, which could spit out some
spotty drizzle or light showers at times. The gradient will
gradually relax later Friday afternoon and evening as the center
of the sprawling high passes to our north. Any late day clearing
will have little impact on high temps given that 850C temps near
0C will only support highs reaching the upper 40s to mid 50s,
warmest in the Cumberland Valley. Once the winds slow and skies
clear Friday evening, temperatures will easily drop off into the
30s. Moist ground conditions and elevated stream levels will
likely lead to fog formation in the main stem river valleys while
the less fog-prone valleys see areas of frost. Any fog and frost
Saturday morning gives way to a mostly sunny but cool afternoon
with highs reaching the mid 50s to lower 60s.

Surface high pressure departs off the Atlantic Seaboard Saturday
night. Meanwhile, a sharpening, high amplitude trough fosters a
clipper system sailing through southern Canada and supports a fast-
moving strong cold front dropping southeast into the Ohio Valley.
Ahead of this front, increasing clouds and a warmer southwest
return flow should keep the PBL mixy for most areas through the
night, holding temps in the 40s for most. A few sheltered valleys
in far east Kentucky could still drop into the high 30s. By
Sunday morning, that moisture-starved front will on our doorstep
over northern Kentucky and quickly blow through with little more
than low clouds, sprinkles and a blustery southwest to northwest
wind shift. Temperatures may initially recover into the 50s, but
strong CAA will cause temps to hold steady or even fall during the
afternoon hours. Temperatures continue tumbling Sunday night as
many of the models indicate 850 temps faller to near -6 to -10 C
by 6z Monday. Post-frontal winds remain quite strong through the
first half of the night, likely leading to an advective freeze
over the higher elevations. If skies clear and winds decouple
later in the night, then a killing freeze would also be likely
through the valleys. Low temps are currently forecast to range
from the mid 20s to low 30s. Interestingly, portions of eastern
Kentucky may end up downwind of a favorable fetch off of Lakes
Michigan and Superior Sunday night while temperatures at the base
of the capping inversion drop to near -10C -- a key temperature
for ice crystal formation/growth. Could the high terrain see the
first flakes of the season? A dry warming trend begins Monday and
persists through mid-week as daytime highs warm to near normal
levels in the 60s on Wednesday and night lows range through the
30s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
ISSUED AT 750 AM EDT WED OCT 28 2020

The lower CIGs have developed and will only lift slightly through
the morning hours before lowering again with the development of
rain showers later in the afternoon and especially this evening
into the overnight. Any river valley fog remaining out there will
clear out shortly. The winds will remain light through the TAF
period, but there is a small potential for LLWS in the Cumberland
Valley by dawn Thursday.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from this evening through Thursday afternoon
for KYZ087-088-118.

&&

$$

UPDATE...GREIF
SHORT TERM...GREIF
LONG TERM...GEERTSON
AVIATION...GREIF


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