JKL issues Area Forecast Discussion (AFD) at Sep 5, 4:10 AM EDT
623
FXUS63 KJKL 050810
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
410 AM EDT Thu Sep 5 2024
.KEY MESSAGES...
- Above normal temperatures but still comfortable humidity levels
will prevail through Friday followed by another cool down over
the weekend.
- Showers, and a small window for thunderstorms, return to the
area on Friday evening and overnight as a healthy cold front
moves through the region.
&&
.SHORT TERM...(Today through Friday)
Issued at 355 AM EDT THU SEP 5 2024
07Z sfc analysis shows high pressure still off to the northeast
of Kentucky but having more of an effect on our weather this night
than last. As a result, skies are mostly clear - away from the
Tennessee border - with a return of fog in the river valleys -
locally dense. Also returning is good radiational cooling over
most of the area resulting in a decent ridge to valley temperature
difference early this morning. Specifically, readings vary from
the lower 60s on the hills to the low and mid 50s in the
sheltered spots - coldest north. Meanwhile, amid light winds,
dewpoints range from the lower 50s north to the upper 50s and
lower 60s south.
The models, and their individual ensemble suites, are in quite
good agreement aloft through the short term portion of the
forecast. They all depict weak 5h ridging easing out of the area
today in advance of a a deepening trough diving into the Great
Lakes. This trough enters the Ohio Valley tonight leading to
height falls for eastern Kentucky through the day Friday. As this
trough further sharpens on Friday, its core of energy and forcing
will push closer to this part of the state by evening with
strengthening southwest winds aloft. This feature moves into an
environment with building instability during the day but looks to
arrive too late to maximize the benefit for strong storms through
00Z Saturday. On account of the very small model spread through
the short term portion of the forecast, have again favored the NBM
as the starting point for the grids with little adjustment needed
aside from incorporating more terrain detail into the temperatures
for early this morning and tonight, as well as adding in more CAMs
data for the PoPs on Friday afternoon and into the evening.
Sensible weather features a warm end to the week as ample
sunshine and winds turning more southerly allow temperatures to
climb to and above normal. The lingering effects of departing high
pressure will mean one more night of good radiational cooling and
a resultant moderate ridge to valley temperature split - along
with river valley fog formation through the night. For Friday, a
distinct cold front pushes toward the area from the northwest and
as a result we will see the winds pick up from the south and
southwest along with more in the way of gusts by afternoon. The
front will get close enough by late afternoon and into the evening
enabling the development of convection - mainly just for our
northern counties through 00Z Saturday. A narrow window will
exist where the heat of the day and stronger winds aloft coexist
for the potential of stronger storms before the convective
instability backs off toward sunset.
The changes to the NBM starting point consisted of adding in more
terrain distinctions for temperatures early this morning and then
moreso tonight. Did also lower dewpoints for midday Friday owing
to deeper mixing into a dry layer aloft. For PoPs, also included
details and timing data from the latest CAMs on Friday afternoon
and into the evening.
.LONG TERM...(Friday night through Wednesday)
Issued at 408 AM EDT THU SEP 5 2024
At the beginning of the long term forecast period, troughing aloft
will both deepen and dig into the Great Lakes region. Forecast
guidance indicates that this feature will transition into a closed
upper level low by Friday night, and a well-defined surface cold
front nestled within said troughing will sweep across the Ohio River
Valley as the entire system propagates eastward this weekend. As it
does so, scattered showers will be possible near and along the
frontal boundary. Any convection that develops with this system will
have to rely on dynamic processes like frontal lift and cyclonic
vorticity advection to sustain itself. However, the best forcing
aloft will remain displaced to our NW, and a lack of meaningful
moisture advection into the area beforehand will relegate
instability to only marginally supportive values. The latest
probabilistic ensemble guidance has picked up on the potential for a
narrow tongue of instability to develop along the I-75 corridor
during peak diurnal heating on Friday. If thunderstorms are able to
take advantage of this and develop closer to Cincinnati on Friday
evening, they could move into far NW portions of the forecast area
early on Friday night. The Storm Prediction Center has included
Fleming County in Friday's Level 1/5 Marginal severe weather outlook
for these reasons, but widespread severe weather appears unlikely in
the NWS Jackson forecast with this system. While a few rumbles of
thunder are possible across the western third of the forecast area
before temperatures drop off on Friday evening, the majority of the
area will only see general shower chances. As this katafront
progresses east overnight, the greatest shower chances parallel its
movement. By Saturday morning, rain chances will be confined to our
far eastern counties, and colder/drier air will seep into the rest
of the Commonwealth on the backside of this system.
The rest of the long term forecast is driven by the return of
ridging. At the surface, a high pressure system will drop down into
the Ohio River Valley from Canada after FROPA on Saturday. This
feature will gradually expand and propagate eastward through next
week, aided by ridging building back in aloft. Under this synoptic
pattern, expect mostly clear skies and efficient diurnal
warming/cooling/mixing processes to yield in ridge/valley
temperature splits, AM valley fog potential, and perhaps a few
broken low temperature records. The Canadian roots of the airmass
associated with the aforementioned high hint at its rather chilly
nature, and the cold air advection processes in place on Saturday
and Sunday will keep afternoon highs near 70 degrees. In a similar
manner, overnight lows will dip into the mid 40s across the entire
area this weekend. In sheltered valleys, where boundary layer
decoupling is most likely in analogous weather patterns,
temperatures may dip down even further into the low 40s. Record low
temperatures at our climate sites (Jackson and London) are in the
upper to mid 40s on these dates and thus in danger of being broken.
Things begin to slowly and incrementally warm back up early next
week under the persistence of clear skies and the building upper
level ridge. By Tuesday, afternoon highs (overnight lows) will
moderate back into the 80s (50s) and remain in this range through t
he end of the forecast.
In summary, after a passing cold front brings shower chances to the
area on Friday night/Saturday morning, fall-like weather settles
into the area for the rest of the weekend. Things slowly warm up
next week, but skies remain mostly sunny. Therefore, other than
patchy valley fog in the mornings, the weather in Eastern Kentucky
looks fairly tranquil next week.
&&
.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 150 AM EDT THU SEP 5 2024
Aside from localized MVFR to IFR, and perhaps locally worse,
conditions in fog generally for some deeper valley locations
through 14Z, VFR conditions will prevail through the period. Of
the TAF sites, KLOZ and KSME are more probable to be affected.
Winds will be light and variable through the period.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...GREIF
LONG TERM...MARCUS
AVIATION...JP/GREIF
Source: JKL issues Area Forecast Discussion (AFD) at Sep 5, 4:10 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202409050810-KJKL-FXUS63-AFDJKL)
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