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265
FXUS63 KJKL 231113 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
713 AM EDT Mon Sep 23 2024

.KEY MESSAGES...

- A potential for showers and thunderstorms will persist through
  much of this week.

- High temperatures will climb into the mid 80s today, then trend
  downward through the week.

&&

.UPDATE...
-- Changed Discussion --
Issued at 713 AM EDT MON SEP 23 2024

Overnight convection is exiting the area. Surface stations and
regional satellite confirm the development of fog across the area
this morning where clearing is taking place. Fog will gradually
dissipate through the morning after sunrise. For now, just
tweaked grids to incorporate latest surface obs. No changes
required for the zones yet. Updated grids have been issued.
-- End Changed Discussion --

&&

.SHORT TERM...(Today through Tuesday)
Issued at 419 AM EDT MON SEP 23 2024

Aloft, flattened ridge continues to be broken down by shortwave
energy associated with a trough moving out of the central Plains
and into the Ohio Valley. This trough manages to make it into
eastern portions of the Commonwealth by the end of the short term,
just as another, deeper system drops southward into the Missouri
Valley. At the surface, a nearly stationary frontal zone is
positioned along the Ohio River just to our northwest. This
feature, combined with passing disturbances aloft, will provide a
focus for sporadic episodes of showers and thunderstorms across
eastern Kentucky through the period.

Sensible weather features a generally unsettled short term, with
periods of showers and thunderstorms impacting different portions
of eastern Kentucky, as well as the region, at times through the
short term. H850 temps between 16-17C combined with the increased
cloud cover and higher potential in PoPs will help keep afternoon
highs in the upper 70s to mid 80s through the period, or about
5-10 degrees lower than the recent upper 80s to lower 90s we have
been experiencing.

The Storm Prediction Center has our area in a Marginal risk for
severe weather today and again on Tuesday. In addition, the
Weather Prediction center has our area in a Marginal risk for
excessive rainfall. Overall, the risk for strong to severe storms
will be conditional, as is often the case it seems. Today, we will
see marginal instability, on the order of 500-1000 J/kg of MLCAPE
and bulk shear is lacking, generally less than 25kt, though it
does increase to around 30 kts tonight. Mid-level lapse rates are
modest, climbing to around 6 C/km. However, there is a relative
lack of triggers through much of the day as the better, more
organized shortwave energy holds off until later tonight and
Tuesday. Thus we will be dependent on the surface front to our
northwest and differential heating to help initiate convection
today. This suggest convection will be more isolated to scattered
today, and less organized. But there are enough ingredients in
place that a strong storm or two could not be ruled out. Tuesday
appears more favorable for strong to severe storms with MLCAPEs on
the order of 1000-2000 J/kg, and bulk shear of 40-50 kts.
However, mid-level lapse rates are weaker. In addition, it is
likely that there will be more cloud cover across the region on
Tuesday. Consequently, severe weather potential will be increase
with more sunshine...or heating. Shortwave energy appears more
organized on Tuesday. Thus convection, as well as the potential
for strong to severe storms appears more likely on Tuesday.

Storm motions are decent through the period, 10-15 kts today,
increasing to around 30 kts or greater by Tuesday. Freezing levels
are generally less than 13 kft and PWATS max out at around the
75th percentile, climatologically. Thus conditions are not ideal
for widespread flooding issues. Everything considered, feel that
any hydro issues will be localized, and more dependent on how
organized convection becomes and the potential of training and/or
the back building of storms over specific locations.

.LONG TERM...(Tuesday night through Sunday)
Issued at 501 AM EDT MON SEP 23 2024

There are two large scale features which will interact with each
other and dominate our weather during the long term period. One of
these is a high amplitude upper trough which will start the
period over the Great Lakes and Mississippi Valley. The other is a
tropical system which will evolve from the area of unsettled
weather currently off the east coasts of Honduras and Nicaragua.
The upper level trough will be drawing on deep mid/upper level
moisture being pulled north from a fetch along the western Gulf
Coast. Precip is expected to be ongoing over at least part of the
area at the start of the period. Models indicate, to varying
extents, a dry slot wrapping around the trough. Because of this
feature, a POP gradient is placed across the JKL forecast area
Tuesday night and Wednesday, with the highest POP in southeast KY
and the lowest in the Bluegrass region. Confidence in the exact
placement of features at that time range is not high, so the POP
pattern represents the best estimate based on the most recent
model runs. The dry slot degrades on Wednesday and Wednesday night
and a more generalized, decreasing POP blankets the area. This
happens as the upper trough develops a pronounced closed upper low
to our west.

By the time we get to Thursday, models suggest the tropical
system will be a hurricane moving north through the Gulf of
Mexico, with its moisture starting to get drawn north around the
extratropical upper low to our west. Both the ECMWF and GFS have
the upper low capturing the tropical system and track its remnants
north through KY on Friday. Have used an increasing POP on
Thursday night as it approaches, with a peak of 60-70% on Friday.
This is influenced by the latest available model runs of the GFS
and ECMWF, and is higher than the latest available national blend
of models.

Once the weakening tropical system departs to the northwest,
models show another dry slot wrapping around the upper low and
reaching us Friday night and Saturday. This results in a relative
minimum in the POP. By the time Sunday rolls around, model
solutions begin to diverge more. The GFS weakens the upper low
and tracks it east over KY, while the ECMWF weakens it but lets it
meander further west. Either way, the dry slot influence would be
waning and the POP creeps a bit higher once again.

&&

.AVIATION...
-- Changed Discussion --
(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 713 AM EDT MON SEP 23 2024

Flight conditions across the area are dropping this morning where
clearing is taking place. These lower flight categories will
persist for a couple hours at the beginning of the period, but
gradually improve after sunrise.

A surface cold frontal zone is draped along the Ohio River just
to our northwest. Subtle disturbances will be tracking through the
Ohio Valley, kicking off some showers and thunderstorms at times
through the period. Activity could be described as sporadic and
diverse in nature, making it more of a forecast challenge with
respect to timing weather at any given terminal. In general, feel
predominant VFR flight conditions is a reasonable forecast, but
there will be drops in flight conditions, particularly VSBYS where
showers and thunderstorms do pass. Model guidance, and especially
higher resolution short term convective allowing models show an
uptick in convection late this afternoon across the area, and with
low confidence in the exact evolution of weather today, tried to
stay close to that guidance. Winds will be light, generally from
the west through the day, except in the vicinity of any
thunderstorms where winds could become gusty.
-- End Changed Discussion --

&&

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

$$

UPDATE...RAY
SHORT TERM...RAY
LONG TERM...HAL
AVIATION...RAY