Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 200625 AAD
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
125 AM EST Thu Feb 20 2020

.UPDATE...
Issued at 125 AM EST THU FEB 20 2020

Only minor adjustments have been made to hourly grids. This led
to no substantial changes at this time.

UPDATE Issued at 1052 PM EST WED FEB 19 2020

The forecast was largely on track, and the only changes were to
blend late evening obs into the forecast.

UPDATE Issued at 903 PM EST WED FEB 19 2020

Two main issues to address in an update. First, temperatures
tonight. With light winds and only some high thin clouds around,
valleys are dropping off more quickly than ridges in the eastern
portion of the forecast area. Clouds will eventually thicken to
the point that it impedes falling temps. However, the cooling that
is expected first has necessitated a lowering of the temperature
forecast.

The second issue concerns precip on Thursday. Models have trended
higher with their QPFs for our southern counties. This would be
more concerning if temperatures were to remain below freezing.
However, at this point, it looks like valleys will climb above
freezing, which will prevent much snow accumulation. This update
does increase the POP slightly in Bell and Harlan counties, with a
60% POP near the state line, and it does allow for an inch or two
of accumulation on the tallest ridges.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 400 PM EST WED FEB 19 2020

20z sfc analysis shows high pressure off to the northwest of the
area keeping the winds from the north to northeast at 5 to 10 mph
across the area. In addition the bulk of the clouds cleared out
through the day leaving behind plenty of sunshine. Despite the
winds advecting in colder air through the day the return of
sunshine helped propel temperatures into the 45 to 50 degree range
this afternoon. Meanwhile, dewpoints have dried out for most of
the area with values falling into the low to mid 20s.

The models are in excellent agreement aloft through the short term
portion of the forecast. They all depict fast and flat flow at mid
levels tilting in response to a trough coming out of the Northern
Plains tonight. This trough sweeps through Kentucky later Thursday
and Thursday night with a healthy band of energy and some height
falls. In the wake of this system heights will start to rebound
but slowing northwest flow will remain over the area into Friday
morning and beyond. Given the limited model spread have favored
the newly available NBM 3.2 for a starting point with the grids
while leaning on the CAMs and NAM12 for details - mostly via the
use of CONSShort for PoPs.

Sensible weather will feature clouds increasing from the
south tonight and lowering toward dawn. This will limit the
temperature drop off through the night. A developing sfc wave on a
stalled front south of the area will move north toward southeast
parts of the CWA for midday Thursday. This system brushes by this
part of the state by Thursday afternoon, but not before
potentially sending enough moisture into the colder air to result
in a touch of snow. A passing 300 mb jet will move over the Ohio
River on Thursday with a brief pocket of upper level divergence
and lift passing over eastern Kentucky Thursday morning into the
afternoon. This will keep a threat of pcpn in the form of snow in
the forecast, but mainly south of the area. This threat drops off
quite quickly northwest of the Middlesboro area to mainly just
flurries for the bulk of eastern Kentucky. The best chance for any
accumulations will be on the higher peaks in southern Bell County
where up to a half an inch of accumulation will be possible
- though mitigated by the ground temperatures warming this
afternoon and not dropping off all too much overnight. Have split
off our far southeast counties with terrain for a potential of
light snow in the HWO. With temperatures reaching the upper 30s by
Thursday afternoon any pcpn may end as a touch of light rain in
the far southeast, as well. The sfc low responsible for this pulls
away Thursday night taking the clouds along with it allowing for
a chilly night with some small terrain differences.

Made only minor adjustments to temperatures from the NBM through
the short term period. As for PoPs - went with the CONSShort
values for Thursday rather than the too low NBM.

.LONG TERM...(Friday through Wednesday)
Issued at 340 PM EST WED FEB 19 2020

The extended portion of the forecast begins on Friday with a
progressive and low amplitude upper level pattern in place. On
Friday, a passing mid level ridge will remain in place through
Saturday night before it shifts off to the west. At the surface, a
strong high pressure center will keep dry weather in place Friday
through Sunday afternoon before the next system begins to impact the
area. The air mass settling in place to start the extended will
bring some Arctic air into the area and with clear skies and light
winds in place, some colder valley temps in the lower teens and
ridges in the lower 20s are possible for Saturday morning. In
addition, models have been trending slower on bringing this next
system in for Sunday. Thus, clear skies will be in place for much of
the night Saturday night as well, leading to ridge to valley
temperature differences here as well. Thus have some of the deeper
valleys in the lower 20s and ridges in the upper 20s given the
slightly modified air mass.

The slower arrival of the next system and southerly flow entering
this system will mean that surface temps will be warmer with precip
beginning as rain and stay rain through the entire event. The
progressive flow of the upper level pattern and lack of
baroclinicity will mean that instability will be weak with this next
system and will only yield around 0.50 QPF at best from Sunday night
through Tuesday. The mention of the lack of colder air will mean as
well, precip behind the front at this time will remain as rain. A
weak low level jet and and low level inversion with the low pressure
system on Sunday night into Monday will lead to some surface winds
gusting to around 25 mph at best. The only other concern into the
extended beyond Monday is the variability in the pattern. For the
most part, temps are trending well above normal with every cold air
shot only bringing temps to more normal values. Thus, the extended
yields little concern for hazards and none will be mentioned in the
HWO.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 125 AM EST THU FEB 20 2020

VFR conditions are expected to linger areawide until around 14Z,
before ceilings and or vis drop into the VFR range near portions
of the TN and VA borders as snow or a mix of snow and rain
arrives with this departing toward 23Z or 0Z as the sfc low moving
across the southeast moves further away from the area. There is
some uncertainty as to how far north the MVFR could make it with
it briefly reaching SME to LOZ to PBX not out of the question.
However, at this point have kept all 5 TAF sites VFR as MVFR
should remain south of a SME to LOZ to SJS line. Winds will
average out of the north at less than 10KT through the period.

&&

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

$$

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



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