-- Discussion containing changed information from previous version are highlighted. --
055
FXUS63 KJKL 181938
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
338 PM EDT Sat May 18 2024

.KEY MESSAGES...

- An upper level trough advancing slowly toward us from the west
  will continue to support showers and thunderstorms into Sunday,
  with the focus shifting southeastward in our area with time.

- Upper level ridging moves into the area from the northwest
  tonight and Sunday bringing drying, with dry weather expected
  area wide from Sunday night through Tuesday night.

- The upper level ridge shifts to our southeast by Wednesday. A
  series of upper level waves and an approaching cold front will
  bring the potential for rain back Wednesday into Friday.

- The upper level ridge passing over will result in warmer
  weather, with above to well above normal temperatures forecast
  Sunday through Wednesday.

&&

.UPDATE...
Issued at 117 PM EDT SAT MAY 18 2024

Renewed surfaced based deep convection is trying to get started,
but is still very small and sparse. Today`s model runs have backed
off on it once again. Have adjusted the POP downward a bit. Will
wait to see what`s going on right before the afternoon package
goes out to see if further adjustments are needed. Have also
lowered max temps slightly, mainly in southeast KY where
persistent clouds have slowed the rise.

UPDATE Issued at 925 AM EDT SAT MAY 18 2024

Fog is lifting and dissipating, and the Dense Fog Advisory which
was in place in the northern part of the forecast area has been
allowed to expire. However, have raised sky cover this morning,
with satellite showing most places currently overcast.

UPDATE Issued at 651 AM EDT SAT MAY 18 2024

Given radar and observed trends, we expanded at least 15 PoPs
through the forecast area this morning, though activity for the
next several hours should stay primarily south of the Mountain
Parkway. Also raised PoPs for this afternoon, especially across
the north, using a blend of the NBM, CONShort, and GFS1hr models.

&&

.SHORT TERM...
-- Changed Discussion --
(Today through Sunday)
Issued at 349 AM EDT SAT MAY 18 2024

Fog has developed and become quite dense this morning especially
from Interstate 64 north, so have issued a Dense Fog Advisory
there. Cloud cover and shower activity has made detecting fog of
Interstate 64 more difficult. It appears the presence of these
clouds and precipitation are providing just enough insolation so
far to keep widespread dense fog from developing. However, if
observations show an increasing trend of lower visibilities more
consistently below one-half mile, a Special Weather Statement or
Dense Fog Advisory could be issued.

Otherwise, a slow-moving upper trough is poised to cross the
region today with light winds aloft becoming more northerly
tonight. This northerly flow will help shunt the deeper moisture
toward the southeastern Kentucky, with decreasing moisture toward
the Bluegrass region. The result will be shower and thunderstorm
chances today favoring southeastern Kentucky where there will be
categorical (75+%) PoPs, trailing off to chance (40-54%) PoPs
along and north of Interstate 64. Drier air will slowly work south
through tonight and help to diminish precipitation from northwest
to southeast.

Fog and low ceilings this morning will give way to sun breaks and
thus destabilization by midday into the afternoon, and with little
in the way of any capping mechanism, showers and thunderstorms
should quickly develop by early afternoon and persist into the
evening. As skies begin to clear tonight, expect widespread fog
formation, with potentially dense fog in the deeper sheltered
valleys especially if there is any substantial clearing.

A much drier air mass builds into the area from the north and
northeast Sunday, but there will be modest moisture and
destabilization remaining especially over the higher terrain along
the Virginia border, which warrants at least slight chance PoPs to
low-end chance PoPs for those areas.

The high temperature forecast for today continues to trend slowly
upward into the mid to upper 70s, capped by extensive low cloud
cover in the morning and then expected shower and thunderstorm
development early to mid-afternoon. Lows tonight will fall into the
upper 50s to near 60 degrees as cooler air advects into the region,
with widespread fog formation preventing temperatures in the valleys
from falling more than about 5 degrees below the ridgetops in the
mid 50s. Despite the light northerly flow Sunday will feature a lot
more sun than in previous days, with highs thus warming into the
lower 80s.

.LONG TERM...(Monday through Saturday)
Issued at 338 PM EDT SAT MAY 18 2024

The period begins with shortwave ridging extending into the
Northeast states. This ridging will keep the weather quiet and warm
through mid week ahead of an advancing cold front, with good
agreement noted in the ensembles and deterministic guidance. The
afternoon high temperatures Monday and Tuesday are forecast to climb
into the mid to upper 80s. By Wednesday, we see the leeside low that
develops Monday night will be pushing northeast into the Great Lakes
and Canada by Tuesday night. While there are slight differences in
the guidance during this period the overall pattern looks fairly
close.

It gets a little trickier across the Ohio Valley going into mid-
week. This is because the various ensembles and deterministic are
struggling on how far south and east this cold front can go given
it looses the greater upper level support and the low pressure
pushes northward further into Canada. Right now, it looks like the
diffuse cold front would arrive Sometimes Wednesday night into
Thursday. This would usher in better chances of showers and
thunderstorms, with around a 20-40 percent chance Wednesday and
50-60 percent chance Thursday. Now there have been some indication
in machine learning products of severe weather potential with
this system. If this was to occur it would be late Wednesday into
Wednesday night before better storms arrive based on the latest
trends. However, confidence is low given the better shear and
instability stay northwest of the area.

Past this the guidance becomes more divergent, but it looks like
another mid-level shortwave rides in Friday. This would lead to a
renewed chance of showers and thunderstorms going into the weekend,
as an area of low pressure forms along the left over boundary
mentioned above. The best chances of showers and thunderstorms
right now would be Friday at 50-60 percent.
-- End Changed Discussion --

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 238 PM EDT SAT MAY 18 2024

A mix of VFR and MVFR conditions (due mainly to ceilings) were
present at the start of the period. While most showers present
during the morning had dissipated, renewed development with
daytime heating/destabilization was starting.

A general improvement to VFR is expected by late afternoon as
ceilings continue to rise. However, additional development of
showers and possibly thunderstorms will lead to localized
sub-VFR conditions in the heavier precipitation. The showers and
thunderstorms will die out this evening and most clouds will dry
up. Good radiating conditions will lead to development of valley
fog late tonight. It will grow in breadth and depth through dawn,
but exactly how widespread it becomes is uncertain. At this
point, the best estimate is that TAF sites will be IFR at least at
times. The fog will dissipate early Sunday morning, leaving VFR
conditions through the end of the period.

&&

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

$$

UPDATE...HAL/CMC
SHORT TERM...CMC
LONG TERM...DJ
AVIATION...HAL