-- Discussion containing changed information from previous version are highlighted. --
494
FXUS63 KJKL 200025 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
825 PM EDT Thu Sep 19 2024

.KEY MESSAGES...

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- Above average temperatures, around 10 degrees above normal (in
  the upper 70s for highs), are expected for the weekend.

- Shower and storm chances return early next week.
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&&

.UPDATE...
-- Changed Discussion --
Issued at 825 PM EDT THU SEP 19 2024

00Z sfc analysis shows a weak pressure pattern through the region
and that is not strongly influencing the weather for eastern
Kentucky as the diurnal trends dominate. As such, the earlier
showers have faded out along with the instability with most of the
mid level clouds to follow shortly. This sets up another decent
night of radiational cooling with potential lows capped by the
relatively high dewpoints still in place - low and mid 60s south
but in the drier mid and upper 50s north. Temperatures are running
in the low 70s in the valleys and upper 70s to lower 80s on the
ridges as the typical relative elevation based split is underway.
The current forecast has this well in hand along with the
potential for fog in the river valleys - especially south. Did
update the forecast to take out the sensible shower chances per
the radar trends and CAMs guidance. Also, the latest obs and
trends were included in the T/Td/Sky grids. These adjustments
have been sent to the NDFD and web servers along with a freshening
of the zones and SAFs - removing early evening shower chances.
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&&

.SHORT TERM...(This evening through Friday night)
Issued at 433 PM EDT THU SEP 19 2024

Included a pre-period in the zone issuance for the late afternoon
isolated rain showers across the area. But activity is waning
quickly with the loss of better heating. SPC mesoanalysis is
showing all the best instability to our southeast as well (MLCAPE
500-1000 J/kg). Thus removed any mention of late day thunder for
our area. Regional radar mosaic shows lightning well to our
southeast, which also supports removing thunder.

Ridging over the south central CONUS is being flattened by an
upper level low and short wave energy tracking across the Upper
Midwest. In general this ridge aloft remain in place over our area
through the short term but does weaken enough by end of the
period that a short wave disturbance is able to flirt with eastern
Kentucky. At the surface, high pressure centered over eastern
Canada but nosing into the Ohio Valley will yield to an
approaching surface cold front late in the period, that will drop
southeast to the Ohio River late Friday night.

Sensible weather features a seasonably warm and dry short term.
With H850 temps between 18-20C Friday`s afternoon high
temperatures in the mid to upper 80s will be 10-15 degrees above
normal. Overnight lows will dip into the 50s within our typically
cooler valley locations, especially in the east, and bottom out in
the milder mid 60s along the thermal belt (ridge lines). No
significant weather to deal with other than our typical valley
fog, which will probably be a bit less dense tonight versus this
morning, at least that is what guidance would suggest. With a full
day to mix our the boundary layer, allowing surface Tds to drop
well into the 50s across our north, did not see any reason to go
against guidance. However, cross over Tds over our southern zones
is only in the lower 60s, close to forecast lows. Thus, the
Cumberland River basin may be the area to watch as far as areas
that more robust fog could develop.

.LONG TERM...(Saturday through Thursday)
Issued at 542 PM EDT THU SEP 19 2024

The pattern starts to increase in activity through the extended.

Starting with Saturday morning, a weak cold front will be dropping
south into the state, eventually passing through east KY during the
afternoon hours. As it moves southward through the state it will be
moving into a stable atmosphere, causing it to continue losing
strength. WPC only analyzes the front through 0Z Sunday, by 12Z they
show it having dissolved. Because of this, most of the impacts from
the system will be across the northern CWA, with pops dissipating as
the system drops south later in the day. Since we are along a
frontal boundary, and temperatures are topping out in the mid-80s
ahead of the frontal passage, can`t rule out a few thunderstorms
developing. However, just like the weak nature of the system, not
too concerned with strong instability or severe weather.

Unfortunately, even once the front passes through, there will be
little reprieve. A strong upper level low will be present across
central Canada, causing a trough to begin digging across the north-
central Conus. KY will find itself in SW flow, therefore, as a ridge
remains across much of the Appalachian region of the Conus. With SW
flow in place in the upper levels, and an approaching cold front in
the lower levels connected to this same system also promoting SW
flow, warm and more humid air will easily advect in. Therefore,
temps are still expected in the upper 80s on Sunday afternoon,
similar to that of Saturday, despite the cold front having moved
through.

The system will continue to progress eastward, with the cold front
attached the surface low in Central Canada. As this continues to
near KY, the warm/humid airmass will be conducive for shower and
thunderstorms development. So far the models are keeping eastern KY
dry through the day Sunday, but does start to show pops moving into
the CWA late Sunday night, covering much of the area during the day
Monday. Pops will diminish a bit overnight, but will return on
Tuesday, reaching their peak as the front moves into the western
portion of the state by the afternoon. At this point the front will
likely stall as a secondary upper level trough continues to dig into
the Great Lakes and Ohio Valley. If this occurs, precip chances will
likely continue through the rest of the forecast period. This
secondary upper level low and trough would also pull in cooler air
from Canada, helping to drop temperatures back to more seasonal
normal values by the end of the forecast period. This may prohibit
instability, as is currently shown in the NBM, with mainly only
showers forecast for Wednesday and Thursday.

&&

.AVIATION...
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(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 800 PM EDT THU SEP 19 2024

Predominant VFR flight conditions expected through the period.
Exception will be KSME and KLOZ where fog is expected to impact
those stations for several hours during the time leading up to
sunrise. However, guidance suggest impacts on VSBYS will not be as
large as this past morning. From all appearances, a cu field will
redevelop again on Friday and have included that in the grids.
Winds will be light and variable through the period.
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&&

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

$$

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