686
FXUS63 KJKL 022130
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
530 PM EDT Tue Jul 2 2024

.KEY MESSAGES...

- Warm and humid weather continues for Wednesday to Friday and
  afternoon heat indices may reach near 100 in some locations
  Wednesday through Friday.

- Dry weather lasts into early Wednesday afternoon, then the
  potential for showers and thunderstorms returns and lingers into
  the weekend.

- The highest probability of rain is on Thursday and Friday and a
  few thunderstorms could produce strong to damaging wind gusts.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 450 PM EDT TUE JUL 2 2024

Late this afternoon, an upper level ridge of high pressure was
centered over the lower MS Valley into the Southeast and extended
across much of the eastern Conus as well. The axis of this upper
ridge is currently west of eastern KY, but return flow in the
lower levels as ushered warmer and more moist air back into the
region. PW is currently analyzed in the 1.2 the 1.6 inch range
with the lower values in the north and east and the higher values
near Lake Cumberland. Dewpoints have risen about 10 to 20 degrees
compared to 24 hours ago while temperatures are on average about
10 degrees warmer as well. With the increase in moisture rather
extensive, but shallow cumulus has developed across the region
with some cirrus passing overhead at times as well. Meanwhile an
upper level low was centered near the Manitoba and Ontario border
with an associated upper level trough south across the Northern
Plains and into parts of the southwest Conus.

Tonight and Wednesday, the axis of the upper level ridge will
shift east across the OH valley region including eastern KY this
evening and then east of the area overnight. Upper level ridging
will remain anchored over the southeastern Conus to the eastern
seaboard. At the same time, the upper level low is expected to
move toward Hudson and James Bay and begin to merge with a deeper
upper low and trough over Southern Canada. A shortwave trough
should move across the upper MS Valley to western Great Lakes
tonight and then across the eastern Great Lakes and into Quebec.
Another shortwave trough moving around ridging in the eastern
Pacific should emerge from the Rockies and into the Plains through
Wednesday afternoon and evening. This shortwave trough should
advance east and reach the mid MS to Lower OH Valley through the
end of the period. Meanwhile, at the surface, a frontal zone
preceding the shortwave trough should reach the Great Lakes
tonight reaching western Quebec to the eastern Great Lakes to the
mid MS Valley to the Southern Plains becoming stationary or nearly
stationary on the southern end. As the upper trough approaches
the boundary should sag to near the OH Valley to end the period.

Dry weather should persist through tonight to midday on Wednesday
as the dominance of ridging begins to dwindle. Further warming
along with an increase in moisture should continue in southwest
flow between departing sfc high pressure and a front beginning to
approach. PW is forecast to climb to to the 1.4 inch southeast to
1.8 inch range west and northwest by Wednesday evening and then
to about 1.8 to 2.2 inch range from southeast to northwest to end
the period. Afternoon dewpoints outside of the highest elevations
near the VA border should be in the upper 60s to low 70s. This
will allow heat indices to peak in the mid 90s to near 100 degree
range. The increase in moisture, daytime heating as well as weak
height falls could lead to some convection developing in or moving
into the northwest and perhaps portions of the west by late
afternoon and evening. If convection does not move into that
regions some CAM runs have an outflow moving in that could be a
focus for some convection. Limited instability and shear should
limit storm strength, some storms could produce brief heavy
downpours. Continued increasing moisture, the approach of a cold
front and the approach of a shortwave trough and perhaps a weaker
lead one should lead to coverage of convection increasing into
Wednesday night. Some locally heavy rain is not out of the
question in the more northern areas if convection were to train,
but the probability is rather low.

.LONG TERM...(Thursday through Tuesday)
Issued at 530 PM EDT TUE JUL 2 2024

Independence Day will kick off the long-term period on a steamy and
unsettled note. The weather models are in good agreement at the
start of the period with an upper level high over the Gulf Coast
states while a ridge axis extends northeastward to off the New
England coast. A positively-tilted trough is dropping into the
Northern Plains. At the surface, a frontal boundary will be draped
from the St. Lawrence Valley, along the southeastern shores of
lakes Ontario and Erie, southwest to over the Lower Ohio Valley
and then northwest toward Kansas City.

Model guidance, including the CAMs, suggest that clusters of
convection will be ongoing along the Lower and Mid-Ohio River
south of the boundary on Thursday morning, likely impacting
locations as far south as I-64 corridor (80+% PoP). The chances
for a rain-free start to the day are better further southeast,
decreasing to around 50% closer to the Tennessee and Virginia
borders, where there is decent possibility that the rain threat
could hold off until after midday. This is the portion of our area
that could see the greatest heating and destabilization.
RAP13/NAM12 show MUCAPE values building to between 2,000 and 3,000
J/kg by early afternoon across our southern counties. Meanwhile,
westerlies aloft will increase aloft as the upstream trough moves
into the Midwest, leading to EBWD of 20 to 35 knots. The final
ingredient, a subtle disturbance aloft, will serve as a lifting
mechanism. Given the parameter space, thunderstorms are expected
to become numerous during the afternoon with a few organized
multi-cell thunderstorms possible. Damaging wind gusts are the
primary threat with organized convective lines or clusters though
a few instances of small hail cannot be ruled out. PWATs climbing
to around or exceeding 2.0 inches and warm cloud rain processes
will also favor heavy rainfall rates, though progressive cell
motions and dry antecedent conditions should mitigate the high
water threat. Aside from the rain and thunderstorm threat, look
for a sticky and muggy Independence Day with high temperatures in
the mid to upper 80s and dewpoints in the mid 70s. Convection is
expected to wane heading into Thursday evening and early overnight
with the loss of daytime heating.

The upper level trough then approaches the Ohio Valley late
Thursday night, pushing the frontal boundary toward the
Commonwealth as a cold front, before beginning to dampen on
Friday and Friday night. A similar parameter space for
thunderstorms is expected to develop area-wide on Friday ahead of
the cold front. Consequently, a few more strong to severe
thunderstorms cannot be ruled out, again with damaging wind gusts
the primary threat. The front itself is expected to cross eastern
Kentucky early Saturday before stalling to our south and east on
Sunday. PWATs then fall back to near 1.00 inch across much of the
region, though modestly higher values may linger closer to the
Virginia border. This combined with lingering broad cyclonic flow
over the Ohio/Mississippi Valley, warranted keeping slight chance
PoPs near and south of the Hal Rogers Parkway/Kentucky-80 corridor
on Sunday. Temperature-wise, after another hot, sticky, and muggy
day on Friday with slightly hotter temperatures (upper 80s to
around 90) than Thursday and similar dew points, some relief is in
store for the weekend as dew points retreat into the 60s though
high temperatures will still be in the mid 80s to around 90 for
many locations.

Looking ahead to the new work week, additional upper level energy
will restrengthen the trough over the Central CONUS, possibly
initiating a weak wave of low pressure to ride along the stalled
boundary while yet another weak cold front approaches from the
west. This will bring the renewed threat for showers and
thunderstorms. Temperatures will remain seasonable with highs in
the mid to upper 80s and lows in the mid 60s to around 70.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 208 PM EDT TUE JUL 2 2024

As moisture has increased cumulus has developed in the 4 to 6kft
range, with VFR persisting. This should diminish during the evening
and give way to a bit of valley fog between about 06Z and 13Z. The
valley fog should again not affect TAF sites. Winds should
generally be less than 10KT through 12Z from the southeast to
south, before becoming increasingly southwest at around 10KT for
more western and northwest locations such as KSME, KLOZ, and KSYM
to end the period.

&&

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

$$

SHORT TERM...JP
LONG TERM...GEERTSON
AVIATION...JP