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273
FXUS63 KJKL 190030 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
830 PM EDT Wed Sep 18 2024

.KEY MESSAGES...

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- Shower (and possible thunderstorm) chances will return on
  Thursday, mainly during the afternoon.

- A warming trend will lead to temperatures around 10 degrees
  above normal over the upcoming weekend.

- Active weather returns for the 1st half of next week, with
  showers and thunderstorms possible.
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&&

.UPDATE...
-- Changed Discussion --
Issued at 745 PM EDT WED SEP 18 2024

23Z sfc analysis shows weak low pressure over the region. This is
supporting variable cloudiness and still a few showers roving east
to west through this part of the state. With the waning
instability the threat for thunder has just about ended this
evening. Temperatures have fallen back into the upper 60s to
middle 70s - lowest in the valleys. Meanwhile, amid light winds,
dewpoints are elevated in the mid 60s to lower 70s. Have updated
the forecast to fine tune the PoPs through the evening per radar
and CAMs trends. Did also add in the latest obs and tendencies for
the T/Td/Sky grids. These minor adjustments have been sent to the
NDFD and web servers along with a freshening of the zones, HWO,
and SAFs taking out the thunder mention.
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&&

.SHORT TERM...(This evening through Thursday night)
Issued at 444 PM EDT WED SEP 18 2024

A strong upper level low and surface low pressure system remain
parked to the east of the state, between the Appalachians and the
Mid-Atlantic coastline. This it is not encompassing eastern KY,
however some of the moisture and energy have advected into the
region under the easterly flow. As a result, mainly isolated pop-up
showers and thunderstorms are ongoing at the time of the forecast
issuance across the northeast portion of the CWA. Expect these to
continue through the rest of the afternoon, before quickly
dissipating this evening with the loss of daytime heating/mixing.
This will also pertain to the clouds, with much of the region
expected to clear out.

Then the attention turns to the overnight period tonight. While most
locations will remain dry through this afternoon, we did have some
rain in the last 48 hours, especially in the southeast. With light
winds, clearing skies, and high pressure centered nearby just to our
west providing subsidence, the stage will be set for potential fog
development. In many ways it will be similar to last night, with
some added subsidence as the low continues to move away from the
region. Models are all agreeing that there will be areas to
widespread fog. It will likely be most impactful in the southeast
where the heaviest rain has fallen. Previous forecast went with
dense fog, but both the NBM and ConsShort were suggesting VIS just
slightly above that of dense fog (around 1/3 to 3/4 a mile). Also
both models were also not focusing these lowered VIS`s in the
southeast where it will most likely occur. As for now, kept with no
dense wording, though not under the impression that it won`t occur,
but rather due to the uncertainty of where exactly it will set up
and how widespread it will actually be. Will be interesting to see
how it sets up tonight.

As expected, this fog should begin lifting during the morning hours
tomorrow/Thursday. A similar set up as today is on tap for tomorrow.
The only difference is that with the low continuing to slowly exit
farther away from the state, pop chances will be a bit lower. That
being said, there is still some generally slight chances during the
afternoon in the farthest eastern portion of the CWA. Without a
change in airmasses, temperatures will be very similar to that of
today. The only caveat will be in the SW, where cloud cover
inhibited temperatures from reaching their full potential today.
While only 70s were observed this afternoon, expect highs in the mid-
80s tomorrow, in line with the rest of the region. This is also
assuming that the cloud cover will not be quite as intrusive and
lingering as today. If clouds develop and sit over the same
locations, as they did today, this too could prevent the temps from
reaching their forecasted highs tomorrow.

Again, heading into tomorrow night, not much will have changed
except for another day of drying (for most locations) and
temperatures dropping a few more degrees compared to tonight (high
pressure taking better hold and slightly drier). Models are all
still pointing at fog development once more, especially as we drop
farther below the cross-over temperature. Again, it doesn`t look to
just be confined to the valleys, but rather overspreading much of
the CWA. Since confidence is a bit low on tonight`s dense fog
forecast, the same is even truer for tomorrow night. Did not include
any dense wording at this time, but have no doubt that it could set
up somewhere in the CWA, especially if a location does receive a
shower either today or tomorrow.

.LONG TERM...(Friday through Wednesday)
Issued at 425 PM EDT WED SEP 18 2024

The 18/12z model suite analysis beginning Friday morning depicts
a positively-tilted ridge axis extending from an ~592 dam high
over/near Del Rio, TX northeastward across the Lower Ohio Valley
and then northward across western Quebec. At the surface, high
pressure ridging is situated just east of the upper level ridge
and extends from Labrador southward along the spine of the
Appalachians. Upstream, a mean trough dips south from Canada
across the Northern Plains/Northern Rockies. Another closed low is
crossing Southern CA as it rounds the base of the upper level
trough. Ahead of that upper- level trough, a cold front is draped
from an ~992 mb surface low over northeast Manitoba down through
Duluth, MN and Kansas City, MO and westward to near/over the OK
Panhandle.

Ahead of the cold front, west to southwesterly low-level flow will
advect unseasonably warm temperatures (17-19C @ 850 mb) across
eastern KY by Saturday and Sunday. While portions of the area,
primarily near the VA border, have received a wetting rainfall this
week, many locations further north and west remain very dry (soil
moistures remain lower than 10 to 20 percentile in many spots as
per NASA SPoRT-LIS). Given the low soil moisture values,
decreasing evapotranspiration, and fair skies, stronger sensible
heating warranted nudging daily maximum temperatures upward on
Friday through Sunday toward or slightly in excess of the NBM 75th
percentile while also nudging afternoon dew points toward the NBM
10th percentile. This yields high temperatures mainly in the mid
80s on Saturday and then a few degrees warmer for both Saturday
and Sunday when warmer locales could eclipse the 90 degree mark.
This drying pattern will also support moderate ridge-valley
temperature splits developing each night--expect lows in the mid
50s coolest valleys to mid 60s in the thermal belts.

Looking ahead to new work week, the closed low initially over CA
will eject out onto the Plains Sunday and become an open wave riding
northeastward toward the Great Lakes. This system will be
accompanied by a surface wave riding the aforementioned frontal
boundary across the Plains, Great Lakes, and on into Eastern Canada.
Ensemble clustering shows significant spread developing during this
time as members struggle to resolve additional energy of North
Pacific origin diving into the trough, which could encourage
slowing/amplification of the parent trough, while, at the same time,
another tropical system potentially forms over the Gulf of Mexico.
These factors will have significant bearing upon whether the surface
low is able to push the cold front through eastern KY by the end of
the forecast period. That, of course, will have significant sensible
implications in terms of temperatures and rain chances during the
second half of the long-term period. Given the uncertainties, the
portions of the forecast from Monday onward remain very close to the
NBM with only some minor adjustments for topography. Forecast highs
cool from the mid 80s on Monday to near normal, in the upper 70s to
near 80, on Wednesday. However, temperatures could be substantially
warmer or cooler depending upon the how the pattern evolves.
Precipitation probability, timing, and intensity are also
uncertain.

&&

.AVIATION...
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(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 830 PM EDT WED SEP 18 2024

The convection is winding down over the area with clouds expected
to clear out into the late evening. Models are all continuing to
suggest enough moisture and cooling across the region to lead to
fog formation across eastern Kentucky, including the TAF sites.
Still expect most sites to beginning dropping in VIS after 06Z,
reaching IFR or possibly even LIFR status by dawn. All fog will
begin to clear after daybreak, giving way to mostly clear skies
and another round of (this time VFR) diurnal CU during the daytime
hours of Thursday. Winds will continue to be light and variable
through the period.
-- End Changed Discussion --

&&

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

$$

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