953
FXUS63 KJKL 032033
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
433 PM EDT Wed Jul 3 2024

.KEY MESSAGES...

- Sultry weather continues through Friday. Afternoon heat indices
  may reach near 100 in some locations.

- A potential for rain arrives tonight and lasts at least into
  Friday night. A few thunderstorms on Thursday and Friday could
  produce locally heavy rainfall and strong wind gusts.

- A cold front finally pushes through as we move into the weekend,
  with dry and somewhat cooler and less humid weather arriving.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 430 PM EDT WED JUL 3 2024

Late this afternoon, an upper level ridge of high pressure was
centered across the southeastern Conus and extended into the
Northeast Conus and west to TX. Meanwhile an upper level low was
centered over northern Canada with a broad trough to the south and
southwest into the Upper MS Valley to Four Corners vicinity and
another upper level ridge was in place over the eastern Pacific. At
the surface, a frontal zone extended from Quebec to the eastern
Great Lakes to mid MS Valleys to the southern Plains with a ridge of
sfc high pressure extending from the Southeast Conus to off the
eastern seaboard. Southerly flow continues to advect a warm and
moist airmass into the region with  dewpoints in the mid 60s in the
higher terrain along the VA border and then upper 60s to low 70s
elsewhere. Meanwhile, PW continues to increase with about 1.5
inches in Pike County to near or in excess of 1.8 inches in the
west. Ahead of the boundary, convection has developed from OH
southwest into portions of IN and western KY. An isolated shower has
recently developed to the west of the Lake Cumberland area. Thus far,
cirrus has been thick enough for temperatures in the central and
southern portions of the area from reaching 90 or higher for the
most part.

This evening and tonight, the axis of upper level ridging is
expected to shift east and south with the ridge weakening  a bit. At
the same time, a gradual trend of height falls is expected over the
Lower OH Valley region and the Commonwealth as the rather broad area
of upper level trough begins to expand east into the Great Lakes and
MS Valley. One or more weak shortwaves or impulses may track into or
near the OH Valley late tonight. PW should increase tonight,
especially across the northern two thirds of the region nearer to
the sfc cold front as the boundary sags toward the OH River. PW may
remain near 1.7 to 1.8 in the southeast, but climb to 2 to 2.25
inches further north and west. This would bring PW values well above
the 90th percentile and as high as the 95th to 99th percentile.
Convection ahead of the boundary may spread southeast and into the
area during the evening or possibly an outflow from that activity
may arrive as well. This and the subtle height falls could lead to
isolated to scattered activity mainly in the evening and then later
at night. The highest probability for any storms is north of the
Mountain Parkway. With the boundary becoming nearly parallel to the
upper flow and the high PW values, some spotty very heavy downpours
may occur.

Thursday, the boundary should remain nearly stationary near the OH
River before gradually becoming a bit diffuse while a shortwave
trough/impulse moves across the OH Valley region on Thursday. On
Thursday night, another stronger shortwave to the south of an upper
low moving from the Plains and upper midwest to near the western
Great Lakes approaches the OH Valley preceded by a cold front. PW
during this time should climb to around or in excess of 2 inches
areawide or well above the 90the percentile. With the boundary to
the north and generally parallel to the upper flow, the threat of
some training cannot be ruled out. Although mid level level lapse
rates will be meager, steep low level lapse rates on the order of at
least 7 to 8C/km may develop and MLCAPE may reach at least 1000 to
2000 J/kg in the afternoon to early evening if not a bit higher near
2500 J/kg in the southwest where less heating may contribute to
temps near 90 with mid 70s dewpoints expected. Bulk shear will be a
bit limited though possibly peaking near 20KT in the south and
approach 30KT in the north. This might allow for some multicells or
line segments to form if cold pools were able to amalgamate and
given the high moisture content in the column a microburst or two
cannot be ruled out. Some strong to locally damaging wind gusts will
be a threat with convection for the Independence Day holiday along
with torrential downpours. Coverage of convection may peak during
the afternoon to early evening per recent CAMS and then decrease in
coverage as the impulse departs during the evening, though
confidence in this timing and coverage scenario is not high. In
between shortwaves a lull in coverage in the late evening into the
overnight may occur with a possible uptick in coverage again toward
dawn on Friday ahead of the cold front and next shortwave.

Current dewpoints and guidance suggest most locations will not fall
below 69 or 70 tonight with coalfield ridgetops and more open terrain
areas likely not falling below the mid 70s unless wetbulbing form
convection occurs there. Otherwise, more in the way of cloud cover
is expected in the north on Thursday nearer to the boundary with mid
80s north and upper 80s to low 90s south for highs. Dewpoints should
be well into the 70s with heat indices peaking in the low 90s north
and mid 90s to around 100 south.

.LONG TERM...(Thursday night through Tuesday)
Issued at 255 AM EDT WED JUL 3 2024

The forecast period will begin with mean upper-level zonal flow but
a digging shortwave moving through upper-Mississippi valley will
eject into the Great Lakes. At the surface, a stationary boundary is
draped across the CWA keeping chances of PoP across the area to
start the period but to the west, the aforementioned shortwave will
bring a renewed chance of PoP as a surface cold front approaches the
area. Along and ahead of the front, showers and thunderstorms are
likely through the day Friday into Saturday before the front exits
Saturday evening. Severe chances look to be largely limited with
FROPA as widespread cloud cover will inhibit instability and shear
is fairly weak ahead of the boundary. However, can`t rule out an
isolated severe thunderstorm with FROPA during the day Friday. Also,
there`s forecast 90-99th percentile above climatological
precipitable water values, 2.10" to 2.30", through FROPA is
expected. Which, if these showers and storms are efficient, heavy
rainfall leading to possible hydro issues could be possible before
the front exits on Saturday.

High pressure builds in for Sunday into Monday before another double-
barreled surface low sets up for next week. The first is another
shortwave developing in the upper-Mississippi Valley and ejecting
into the Great Lakes with a cold front crossing through the
Commonwealth. The second feature is a weak surface low riding along
a low-level jet streak. The second feature will bring increasing
showers and thunderstorms to the region Monday afternoon before the
first system drags a cold front through the region on Tuesday.
Showers and thunderstorms are forecast to persist through the day
Tuesday and linger through the remainder of the forecast period.

Overall, the period will highlighted with periods of showers and
thunderstorms that`ll bring much needed rain to the area. Also,
temperatures will return to more seasonal ranges as daytime highs in
the mid-80s to low-90s and overnight lows ranging from the upper-50s
to upper-60s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 225 PM EDT WED JUL 3 2024

VFR is expected to largely prevail through the period with cumulus
and mid level clouds at times. However, an approaching front and
then an a passing disturbance should combine to lead to isolated
to possibly scattered convection at times after 21Z, with the
greater coverage of convection being most probable to end the
period. Within any thunderstorms (with sub-VFR conditions) can`t
be ruled out. Winds will mainly be from the southwest at around
10KT or less during the period, though stronger gusts will occur
in or near thunderstorms.

&&

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

$$

SHORT TERM...JP
LONG TERM...VORST
AVIATION...JP