061
FXUS63 KJKL 040242
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1042 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.

&&

.UPDATE...
Issued at 1042 PM EDT WED JUL 3 2024

The NBM seems to continue to have a good handle on PoPs, so
blended in the latest NBM PoPs with inherited PoPs from the
afternoon forecast package through early afternoon Thursday.
Changes otherwise were minimal, mainly to blend the forecast with
the latest hourly temperature and humidity observations.

UPDATE Issued at 711 PM EDT WED JUL 3 2024

The early evening update raises PoPs along Interstate 64 and
points north in accordance with more CAMS indicating convection
impacting this area this evening into the overnight. Most of these
CAMS indicate that the current activity will move into northern
parts of the forecast area later this evening, generally weakening
as they do so especially daytime heating diminishes.

Other changes were minimal and were to blend in latest observed
temperatures with the forecast for the next several hours.

&&

.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...(Friday through Wednesday)
Issued at 500 PM EDT WED JUL 3 2024

The long-term starts off an an active note as anomalously deep but
dampening upper level trough (for July) passes from the Midwest
on early Friday morning on into Quebec Saturday. This system will
push a cold front across eastern Kentucky between 0 and 12z
Saturday. The front itself won`t bring much of a temperature
change, rather it will bring noticeably lower humidity levels (mid
70s dew points vs. low to mid 60s dew points). In the face of
dwindling upper level support and a persistent upper level ridge
over the Southeast US and Western Atlantic, the frontal boundary
eventually hangs up along the eastern slopes of the Appalachians
by early Sunday. This will allow for an area of surface high
pressure to dominate eastern Kentucky from late Saturday through
Sunday. Meanwhile, additional upper level energy will drop out of
northwest Canada over the weekend and reinforce troughing over the
central CONUS by Monday, though that trough will likewise
propagate northeastward and dampen by middle of the week. As flow
turns southerly over the Ohio Valley ahead this next trough, the
remnant boundary to our south and east will be pulled back north,
allowing higher humidity levels to bleed back into eastern
Kentucky on Monday. As that trough pivots through the Ohio Valley
later Tuesday and Wednesday, it will sweep another cold front
through our area.

Ahead of the first cold front on Friday, the ingredients might
come together for another day of numerous thunderstorms.
Increasing flow aloft is forecast to generate 25 to 35 knots of
effective shear. However, the evolution of overnight convection
upstream could have an impact on how much instability is
realized. If convection or debris cloud cover arrives early in
the day, then the severe threat would be minimized due to
relatively meager instability. Conversely, several hours of
intense surface heating would be supportive of more widespread
strong to severe convection. The RAP13 suggests 1,000 to 2,500
J/kg of MLCAPE which combined with the anticipated shear would be
more than sufficient for organized multicell clusters and even a
line segments. Strong to damaging winds appear to be the primary
severe weather threat. Anomalously high PWATs and warm rain
processes will support torrential downpours; however, relatively
dry antecedent soil moisture, low stream flows and progressive
cell motions should all minimize the flooding concern. Aside from
the severe weather and heavy rain threat, strong surface heating,
assuming that upstream convection does not adversely impact sky
cover, would support highs in the mid and upper 80s on Friday and
dew points in the 70s would buoy heat indices well into the 90s
to near 100F. The shower and thunderstorm threat diminishes from
northwest to southeast on Friday night as the cold front passes,
though a shower could linger into the day on Saturday in those
counties adjacent to the Virginia border. Behind the front, a
noticeably less humid air mass will move in on Saturday while
temperatures drop back a few degrees to mainly the middle 80s
under mostly sunny skies. The fair weather continues Saturday
night and Sunday with cool low temperatures in the upper 50s to
mid 60s and highs in the mid to upper 80s. Looking ahead to new
work week, shower and thunderstorm chances return on Monday as
the humidity returns and lingers until Wednesday when the next
cold front passes. The hottest temperatures of the period are
forecast on Monday with highs in the upper 80s to lower 90s for
most. The heat backs off into the the mid 80s for highs by
Wednesday behind the second cold front.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 724 PM EDT WED JUL 3 2024

VFR conditions are expected to largely prevail through the period
with cumulus and mid level clouds at times. However, an
approaching front and then a passing disturbance should combine
to lead to isolated to possibly scattered convection at times this
evening through the rest of the TAF period, with the greater
coverage of convection being most probable between 14z and 21z
Thursday. Within any thunderstorms sub-VFR conditions can be
expected, with some potential for strong gusty winds with the
stronger storms. Winds will mainly be from the southwest at around
10KT or less during the period outside of thunderstorms.

&&

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

$$

UPDATE...CMC
SHORT TERM...JP
LONG TERM...GEERTSON
AVIATION...CMC