000
FXUS63 KJKL 181548
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1148 AM EDT Thu Apr 18 2024

.KEY MESSAGES...

- One more warm day of temperatures reaching the 80s ahead of a
  pattern change to cooler conditions.

- A cold front with more momentum will approach tonight and pass
  through the area on Friday, presenting at least a likelihood (>=
  70% chance) of showers along with some thunderstorms.

- Cooler and more seasonable temperatures will arrive behind that
  front and carry through the middle of next week.

&&

.UPDATE...
Issued at 1148 AM EDT THU APR 18 2024

Forecast is on track and only insubstantial changes were made by
blending in late morning obs.

UPDATE Issued at 740 AM EDT THU APR 18 2024

As the stratus has started to thin and break up in the south some
valley fog managed to form in the valleys. This will dissipate
over the next hour or so. Have updated the forecast to include
this fog and touched up sky cover. These adjusted grids have been
sent to the NDFD and web servers.

&&

.SHORT TERM...(Today through Friday)
Issued at 440 AM EDT THU APR 18 2024

08Z sfc analysis shows approaching low pressure to the west of the
state while a sagging and dying cold front is settling into this
part of Kentucky early this morning. So far, this boundary has
not been able to generate any convection threatening the CWA but
does appear to be inducing some low stratus over most of the
southern portions of the forecast area. This is in lieu of fog for
most locations. Meanwhile, a well mixed boundary layer - thanks
to continued southwest winds of 5 to 10 mph - has led to mostly
uniform temperatures and dewpoints in the upper 50s to lower 60s.

The models, and their individual ensemble suites, continue to be
good agreement aloft through the short term portion of the
forecast. They all depict the passing of a deep and large trough
through the northern portion of the country - brushing by the
Ohio Valley through Friday evening. This pattern evolution at 5h
will initially pump up heights for eastern Kentucky into the
afternoon before its influence takes them down and switches the
mid level flow to more southwesterly for a time tonight. With
this transition, more energy rides through the area later tonight
in the faster flow at mid levels that turns nearly zonal by
Friday morning. An additional impulse then slips by overhead
Friday afternoon in the continued fast, flat flow. Given the
very small model spread in the short term, the NBM was used as
the starting point for the grids, though the consensus CAMs
guidance was mainly applied to the PoPs.

Sensible weather features the last of the warm days for a bit as
ample late morning and afternoon sunshine, and south/southwest
winds, return high temperatures to the 80s for most places. This
is ahead of an approaching cold front that will push showers and a
few thunderstorms into the area towards midnight. This area of
convection then slowly works east with the front into Friday
eventually clearing by that evening. The main threat for any
strong to severe storms will be with the leading edge of the
convective line that most likely will be weakening due to loss of
the better daytime enhanced instability by the time it gets here.
However, dynamics and jet energy aloft, along with any residual
mesoscale features may be enough to carry the risk well into the
normally convective minimal hours of late at night and into the
morning after sunrise. Additional, though less organized, showers
and storms will be around through the day Friday with the front
clearing out eventually from west to east during the afternoon.
The rain, clouds, and a changing air mass will make for a cooler
day on Friday, as well.

The main adjustments to the NBM starting point were centered
around incorporating the consensus CAMs ideas for PoPs and pcpn
timing tonight through Friday. Did not deviate much from the NBM
guidance for temperatures and dewpoints through the period on
account of the high RH values.

.LONG TERM...(Friday night through Wednesday)
Issued at 447 AM EDT THU APR 18 2024

The large scale pattern aloft to begin the extended will feature a
large northern stream trough of low pressure moving across
southeastern Canada and then out to sea heading into the upcoming
weekend. We may see a few showers and storms lingering across the
eastern third of the forecast area Friday evening, behind the
departing trough. Once this system has cleared region, a weak ridge
of elongated high pressure should settle over the area late Friday
night through early Saturday night. The dry weather will short
lived, however, as a southern stream low pressure system is expected
to move through lower Tennessee Valley on Sunday, and will bring
scattered showers to most the forecast area, generally south of I-
64. This batch of rain is forecast to exit the area by early Sunday
evening, as the southern system moves quickly off to the east.

After the southern system moves away, another ridge of high pressure
will be poised to bring a brief period of dry, albeit much cooler,
weather to eastern Kentucky Sunday night through Monday night. The
ridge will usher in a Canadian air mass, that could provide cold
enough air for some of our deeper eastern valleys to experience
patchy frost late Sunday night into early Monday morning. Yet
another area of low pressure is then forecast to invade from the
northwest on Tuesday, and would bring periods of showers and a few
storms to the area through mid-week. At this time the chances of
thunder with this third system appear to be quite low due to a lack
of instability, but a few storms cannot be ruled out early Tuesday
evening, as low pressure passes by to our north, and a cold front
pushes through the region. this third round of rain should come to
an end early Wednesday evening, as the upper system and cold front
both move off to our east. After that, we should see another brief
window of dry weather. It appears that temperatures will be all over
the place during the extended, ranging from well below normal on a
couple of days, to normal or slightly above normal on others.

With the models not in the best agreement concerning the evolution
and movement of weather systems and the coverage of precipitation
associated with each system, decided to stick pretty close to the
NBM forecast, with only minor modifications needed.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 755 AM EDT THU APR 18 2024

VFR was noted across the northeast TAF sites at issuance time,
with IFR and MVFR CIGs or VIS observed through the Cumberland and
Kentucky river valleys. The low stratus there has started to thin
out and as a result valley fog has developed with some
encroachment to the terminals. This will clear out over the next
couple of hours with VFR conditions returning later this morning
and lasting through the evening. Then the cold front, likely with
a band of showers with a few embedded thunderstorms, moves into
the area in the last portion of the forecast through dawn Friday.
South to southwest winds will set up at 10 kts or less today and
continue that way into the night ahead of the front. Winds will
be more erratic towards dawn Friday as that front makes it deeper
into the area with its convection.

&&

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

$$

UPDATE...HAL/GREIF
SHORT TERM...GREIF
LONG TERM...AR
AVIATION...GREIF