JKL issues Area Forecast Discussion (AFD) at Sep 12, 8:50 PM EDT462
FXUS63 KJKL 130050 AAA
AFDJKL
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
850 PM EDT Thu Sep 12 2024
.KEY MESSAGES...
- Welcome rainfall potential will increase this evening and
continue overnight and into Friday, though amounts will
generally be light and confined to our southwestern areas.
- Unsettled weather with episodic light rain chances mainly in
the south and west will continue through the weekend into early
next week.
- Temperatures will largely remain above normal especially across
the north where it looks quite dry through next week, with near
normal temperatures and better chances of rain in the south.
&&
.UPDATE...
Issued at 850 PM EDT THU SEP 12 2024
00Z sfc analysis shows eastern Kentucky seeing the influence of
the remnants of Francine as it lifts into the western Tennessee
Valley. This has spread mid and high levels clouds over the state
along with some mainly light showers tracking through our
southwest counties - generally west of I-75. Sfc winds have an
easterly component through the JKL CWA and this is maintaining a
downslope element likely limiting the eastern extent of the
steadier rains overnight. Given the cloud cover - that will be
around through the night - temperatures are fairly uniform
currently in the lower 70s (upper 60s in the rain) while
dewpoints vary from the lower 50s northeast to the lower 60s in
the southwest with the rain. Have updated the forecast to fine
tune the best rain chances and better QPF through the night per
the latest CAMs guidance. Did also include the current obs and
trends for the T/Td/Sky grids. These adjustments have been sent to
the NDFD and web servers.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 230 PM EDT THU SEP 12 2024
Remnants of Francine continue to weaken as the system moves
northward through Mississippi this afternoon. Mid/high level
clouds continue to slowly thicken as they spread north through TN
and into southern and central KY. Far northern KY has had a full
day of sunshine and temps have warmed most significantly there
into the lower 80s. In the thicker cirrus and mid cloud over
southern KY, temperatures have held in the middle 70s. An east-
west arc of rain showers across central TN has slowed in its
northeast advancement as easterly flow down the western slopes of
the Appalachians has provided subsidence and mixing of dry air
below the advancing cloud base, eroding precipitation as it tries
to move north toward the KY border. Dewpoints across the JKL
forecast area are only in the lower to middle 50s.
As Francine's low-mid level circulation grinds to a halt tonight
over northeast Arkansas, a rapidly decaying low and mid level
/850-700mb/ wind maximum on the northeast periphery of the cyclone
will shift into southern KY this evening and lift north. The
north/east gradient of this wind maximum will be frontogenetic in
nature and - at least for a time - be accompanied with a focused
band of ascent/theta-e advection which is likely to drive an arc
of rain/showers into the southwestern areas of the JKL forecast
area by mid to late evening. While there is good confidence in
measurable rain in the southwestern couple of tiers of counties of
the forecast area, confidence in amounts above 0.25" rapidly
diminish per 12Z HREF data (only a 30-50% chance mainly for areas
west and south of London). Rain will struggle to penetrate the
higher slopes of the eastern JKL forecast area, and with the
time the forcing tends to weaken/dissipate on the eastern end of
this arc, such that even the chances for measurable rain become
scant north/east of Jackson. This will be aided by continued
easterly / downslope flow off the Appalachian, and a moisture
transport vector that is more sluggish/diminished with time and
favors areas west of the JKL forecast area. Thickening clouds will
keep minimum temperatures higher than in previous nights, and this
should also keep the vast majority of valley fog at bay, though
far north/northeastern areas will need to be watched. It should be
noted that the 12Z CAMS are particularly meager in the QPF in
comparison to the 12Z global/parameterized guidance, some of which
does bring amounts above 0.50" to near 1" in that favored far
western portion of the forecast area. Am trending the forecast a
little away from those heavier amounts, however, in light of the
better forcing remaining west of the area in face of continued
easterly/downslope flow.
Confidence in specific rain chances really starts to take a hit as
we move into Friday, and Francine's closed low/mid level
circulation spins in place over Arkansas and barely moves through
the day, while the entire height field continues to fill/weaken,
as do the attendant low/mid level wind maximum. As a steady
southeast 850mb flow continues in a downslope fashion across the
JKL CWA, no appreciable moisture advection, it's hard to find a
reason to have much in the way of rain chances as the days wears
on after the overnight/early morning forcing dissipates. The flow
is still somewhat convergent across the southwest/west portions
of the forecast area through the day, and there is an increase in
amount of low level moisture overall, so some showers could
continue through the day in episodic fashion, but there's just not
a lot of forcing to hang one's hat on in terms of a higher rain
chance beyond 30-40%. As Francine's closed circulation begins to
finally slide east/southeast into western TN/northern MS, there
may be a brief uptick in convergence/low-mid level moisture
advection again into the areas south/west of London on Friday
evening and night, but the signal is underwhelming for any
meaningful rain chances beyond 40-60% for a few hours and rainfall
would likely be quite elevated in nature....and thus light.
.LONG TERM...(Saturday through Thursday)
Issued at 230 PM EDT THU SEP 12 2024
Saturday will offer the best chances for rain across the JKL CWA
with the remnants of Francine still around. The formation of a Rex
blocking pattern will allow for the remnants to stall out in the
overall synoptic pattern. The flow pattern will also allow for some
moisture advection from the Atlantic, feeding the leftover wave of
low pressure.
Low pressure will continue to weaken over time, but will leave a
subtle troughing feature that will compel a mention of PoPs in the
forecast, especially through the rest of the weekend. By Monday, the
overall forcing will continue to weaken, but will have to keep at
least a slight chance mention for showers given the subtle trough.
By mid-week, high pressure eventually takes over and should keep the
precip at bay. Through this extended forecast period, the high/low
temperature forecast remains fairly similar each day given the
persistent flow pattern.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 820 PM EDT THU SEP 12 2024
VFR conditions will likely hold through the period, though some
rain is expected - mainly for LOZ/SME tonight which - if heavy
enough - may lower visibility briefly into MVFR categories. Overnight
an arc of rain will spread across the LOZ/SME terminals, but
visibility and ceilings are likely to remain VFR most of this
time. The relatively dry boundary layer should allow for a
reasonably strong inversion, probably keeping any higher gusts
associated with Francine's remains to stay aloft. For
JKL/SYM/SJS, still don't see appreciable moisture working this
far north to warrant anything beyond a a possible VCSH period at
JKL with no current mention. SYM/SJS should stay rain-free with a
thickening mid cloud deck down to 10 kft or a little below.
Mid/high level moisture (VFR mid cloud) hangs around into Friday
while any rain bands quickly dissipate and / or shift west out of
the area. Continued light easterly or southeasterly winds can be
expected through the morning and afternoon on Friday.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...GREIF
SHORT TERM...NWS ILN (BINAU)
LONG TERM...NWS ILN (CLARK)
AVIATION...GREIF
Source:
JKL issues Area Forecast Discussion (AFD) at Sep 12, 8:50 PM EDT---------------
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