-- Discussion containing changed information from previous version are highlighted. --
430
FXUS63 KJKL 192033
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
433 PM EDT Thu Sep 19 2024

.KEY MESSAGES...

-- Changed Discussion --
- Above average temperatures, around 10 degrees above normal, are
  expected for the weekend.

- Shower and storm chances return early next week.
-- End Changed Discussion --

&&

.SHORT TERM...
-- Changed Discussion --
(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...(Friday night through Wednesday)
Issued at 513 AM EDT THU SEP 19 2024

The period is expected to begin with a subtropical ridge centered
in the the Southern Plains/TX vicinity, but with narrow ridging
extending northeast into the mid MS and Lower TN Valley regions to
the upper OH Valley. A closed low is expected to be in place
across the southwest Conus with a trough extending from western
portions of Canada south to the Northern Rockies/Northern Plains,
while ridging is expected to be centered well west of the CA
coast in the eastern Pacific. At the surface, a ridge of high
pressure is expected to be centered in VA and extend into the
Carolinas as well as north into the mid Atlantic states with
another sfc high centered in the Lower MS Valley vicinity.
Meanwhile, a sfc frontal zone is expected to precede a lead
shortwave moving across the Great Lakes and western Ontario in
advance of the upper level troughing extending into the Northern
Rockies/Northern Plains. This boundary should roughly extend from
western Ontario to the western Great Lakes to a sfc low in the
vicinity of the southern end of Lake MI. A warm front associated
with that low is progged to extend into the Lower Valley and
perhaps into the northeastern KY/WV border region. Another more
substantial sfc low is expected to be near the Saskatchewan and
Manitoba border a bit north of the border with ND and then extend
into ND to northwest SD to northeastern WY to another sfc low in
MT with a cold front trailing into northern CA. As the period
begins, 00Z LREF mean PW is in the 0.9 inch range in far
southeastern KY in areas near the VA border to about 1.2 inches in
the eastern Bluegrass southwest to the Lake Cumberland vicinity.
At that time, surface dewpoints are progged to be in the upper 50s
to lower 60s.

Friday night to Saturday night, the upper level ridge centered
initially over the Southern Plains vicinity is expected to build
east and northeast into the Southeast while the southern end of
the weak lead shortwave traversing the Great Lakes to Mid Atlantic
states and then off the northeast U.S. coast brushes the OH Valley
and Central Appalachian region. At the same time, the upper level
trough axis extending into the Northern Rockies and Plains to
begin the period is expected to rotate east and then northeast
across the Northern Plains/Upper MS Valley and enters the western
Great Lakes. Another weak shortwave could also near the mid MS
Valley by late Saturday night. In between the two shortwaves, weak
shortwave ridging may work east in between these shortwaves and
into the Lower OH Valley late in the period. Further west, the
closed low over the southwest Conus is expected to meander to the
Four Corners region and to the vicinity of the CO front range
during this timeframe. At the surface, meanwhile, high pressure is
expected to build to the Southern Appalachians and remain in
place through Saturday night while the initial sfc low tracks
north of the area into OH and weakens with a general trend of a
warm front lifting north and northeast of eastern KY. Meanwhile,
the more substantial sfc front ahead of the upper level trough
axis is expected to approach James Bay late in the period and
extend into the western Great Lakes to the Central to Southern
Plains regions late Sat night. PW per the 00Z LREF mean is progged
to reach the 1 to 1.35 inch range by late Saturday night.

Sunday to Monday night, the axis of shortwave upper level ridging
is progged to shift east as the weekend ends and across eastern on
Sunday to Sunday night as another shortwave or two in southwest
flow between upper ridging that becomes oriented from west to east
across the Gulf Coast states and Gulf of Mexico and the upper
level low emerging into the Plains that reaches the mid to upper
MS Valley by late Monday and then the western Great Lakes by late
Monday night. During this time, sfc high pressure departs to the
east with the a sfc low moving along the boundary into the Great
Lakes that weakens while a stronger sfc low moving along the
boundary tracks from the Central Plains/KS vicinity to the mid MS
Valley and eventually the western Great Lakes. With the region in
the warm sector, PW per the 00Z LREF mean should climb to about
the 1.3 to 1.5 inch range in eastern KY by Monday and then remain
at that level. These values would be above the 75th percentile and
fall between the 75th and 90th percentiles

Tuesday to Wednesday, the upper level low is progged to track
northwest of the OH Valley across the Great Lakes and into Ontario
from Tuesday to Tuesday night and merge with another shortwave
trough that will have moved across western Canada to end the
weekend and then emerges into the Canadian to Central and Northern
U.S. Plains by Tuesday and then this trough axis moves to the
Great Lakes to OH valley region including eastern KY to end the
period. The sfc low should move across the northern to central
Great Lakes with the trailing cold front nearing or moving into
eastern KY to end the period.

Enough moisture may be in place on Saturday combined with the weak
passing shortwave and a warm front in the vicinity for isolated
showers and perhaps a storm across the eastern half of the region.
Lower 60s to perhaps mid 60s dewpoints combined with sfc
temperatures well into the 80s and perhaps upper 80s should lead
to at least marginal instability within a weak shear environment.
In the warm sector, chances for convection should be west and
well north and northeast of the area for Saturday night and
Sunday. However, height falls and the potential for a passing
shortwave will lead to chances for isolated convection on Sunday
night with unsettled weather continuing into mid week as multiple
shortwaves cross the Lower OH Valley area and the cold front
eventually approaches. Isolated to scattered pops (20 to 50%) are
forecast for multiple periods from Monday to Wednesday, though all
days may have a diurnal peak. Any rainfall would be welcome
considering our current recent dryness in the southwest portion of
the area to to D0 to D2 status in portions of the eastern
Bluegrass region into northeastern KY south and east to the VA
border.

High temperatures should peak be the warmest of the week on
Saturday at about 10 degrees above normal. It is possible that
some spots could be warmer than the current forecast and touch the
90 degree mark where clouds and or convection do not occur,
particularly in the west and southwest. With a shortwave ridge
crossing the area some of the normally warmer spots and in
particular deeper valley locations/cities in the Big Sandy region
are forecast to reach 90 at this time as highs remain about 10
degrees above normal. The pattern should also support a couple of
ridge/valley temperature splits from Friday night to Sunday night,
with deeper eastern valleys in the mid to upper 50s for Friday
night and Saturday night and near 60 on Sunday night while
coalfield ridgetops and some more open terrain locations only drop
to the mid to upper 60s.

As moisture continues to increase early next week, cloud cover
resulting from deeper moisture and convection traversing the
region should result in high temperatures falling to near or below
normal for Monday to Wednesday with narrower diurnal ranges.
-- End Changed Discussion --

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 148 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 morning. Based on most recent guidance, went with
IFR VSBYS at KSME and MVFR VSBY at KLOZ, roughly from 07/08Z
through 13Z.

Cu field across the area this afternoon will dissipate as we get
closer to sunset. From all appearances, the Cu field will
redevelop again tomorrow. Winds will be light and variable through
the period.

&&

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

$$

SHORT TERM...RAY
LONG TERM...JP
AVIATION...RAY