JKL issues Area Forecast Discussion (AFD) at Jul 30, 5:18 PM EDT253
FXUS63 KJKL 302118
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
518 PM EDT Tue Jul 30 2024
.KEY MESSAGES...
- Thunderstorms, some with strong to possibly damaging wind gusts,
may affect the region this afternoon and evening.
- Daily rounds of showers and thunderstorms could lead to a threat
for heavy rainfall and localized flooding.
- Hot temperatures return for Thursday afternoon with heat indices
ranging between 100 and 105 degrees for many locations.
&&
.UPDATE...
Issued at 234 PM EDT TUE JUL 30 2024
With destabilization occurring in advance of convection over
central KY, this convection appears poised to move across eastern
KY this afternoon to early this evening. Hourly pops have been
increased for this afternoon to account for this probability. The
southwestern portions of the CWA will have the best combination of
instability and shear. Severe Thunderstorm Watch 570 has been
issued accordingly and includes the southwest part of the area
for primarily a wind threat.
UPDATE Issued at 1159 AM EDT TUE JUL 30 2024
In the wake of an overnight to early morning MCS, isolated
convection lingers near the VA border. At this time, there were
some breaks in the cloud cover across the region, allowing for
some airmass recovery to commence. 15Z MLCAPE is analyzed at
about the 750 J/kg in the east to near 2000 J/kg range near Lake
Cumberland. PW ranged from about 1.5 inches northwest to near 1.75
along the TN border. Further heating is expected this afternoon,
with MLCAPE forecast to reach 1500 J/kg in the north and east and
2500 to 3000 J/kg near Lake Cumberland per the RAP. A gradient in
MLCAPE is progged from southern IL/IN across portions of central
KY and toward the JKL vicinity by the late afternoon/evening.
Meanwhile, DCAPE is forecast to climb to the 1000 to 1300 J/kg
range areawide during the afternoon to early evening. Meanwhile,
effective shear is forecast generally in the 20 to 30KT range,
and perhaps as high as 35KT near the TN border in the late
afternoon/early evening.
Isolated to scattered convection should develop as instability
increases during the afternoon and with west northwest flow
persisting, upstream convection could potentially move in the from
the west and northwest later in the afternoon/evening. The
forecast instability and DCAPE combined with shear more on the
marginal end of spectrum support the potential for a few strong to
perhaps severe storms. In addition, mid level lapse rates are
generally forecast around 6 C/km while low level lapse rates are
forecast to rise to around 7C/km and is more favorable for gusty
winds. Wind gusts and heavy rain rates will be the main threats
and with the better alignment of instability and shear in the
south and southwest, chances for both appear best there.
Overall, hourly grids for the next couple of hours were updated
based on recent radar and observation trends and then blended to
the previous forecast by mid afternoon. Further adjustments of
pops will likely be needed as convective trends become more
apparent.
UPDATE Issued at 721 AM EDT TUE JUL 30 2024
QLCS has crossed eastern Kentucky early this morning and is now
exiting into Virginia and Tennessee. Fortunately, other than the
severe wind gust at the Fleming Mason Airport as the line moved
in, observed wind gusts have remained under 40 mph. Behind the
line, a trailing stratiform rain shield and any subsequent spotty
showers should generally diminish over the next couple of hours.
Forecast grids has been blended with latest observations and
recent CAM data. Updates have been sent and published.
&&
.SHORT TERM...(Today through Wednesday)
Issued at 423 AM EDT TUE JUL 30 2024
The regional radar mosaic shows a semi-organized line extending from
Carter Caves State Park to Stanton to just north of
Campbellsville at 815z. Ahead of this activity, weather is quiet
with exception of a storm over western Morgan and southwest
Elliott counties. At the moment, temperatures are holding in the
lower to middle 70s. Some fog is also noted in the deep, sheltered
valleys particularly close the Virginia border. The surface
weather map analysis suggests a warm front extending northward
from Southern Appalachians to an ~1007 mb low over the Lower
Peninsula of Michigan, while a cold front trails back to the
southwest across the Lower Ohio valley and then back across the
Midwest, and then into the Northern Plains as a quasi-
stationary/warm front. Looking aloft, mean 500H ridging is found
over the Plains, while broad troughing is found over the Ohio
Valley/Great Lakes/Northeast US. Multiple vorticity maxes are
passing over the ridge and into the troughing. The first of these
vort maxes is dropping through Lower Ohio Valley this morning and
is supporting a line of showers and thunderstorms dropping
southeastward across the Commonwealth. Ahead of this line, the
parameter space meets all of the requirements for sustaining
healthy convection west of I-75, whereas the instability is
somewhat wanting further east. Analysis suggests moderate
instability (MUCAPE values of ~1,000 J/kg east of US-23 to ~2,000
J/kg west of I-75) atop weak surface-based CIN). A sharp DCAPE
gradient is also noted across the forecast area ranging from
~900J/kg near the West Virginia border up to ~1,400J/kg near Lake
Cumberland. EBWD (20-30kts) and 0-6km mean winds (20kts or a
little higher) are also sufficient for cold-pool driven QLCS
maintenance. While the QLCS has been slow to organize, a recent
gust to 61 mph at Flemingsburg Mason Airport was evidence that at
least portions of the line have strengthened to severe limits and
warranted a severe thunderstorm warning for much of Fleming and
portions of Rowan County.
Expect the QLCS to generally press southeast and cross the entire
forecast area through 12z. While strong to severe elements, mainly
capable of producing damaging wind gusts, are possible anywhere
along the line, the parameter space is most favorable for
sustaining robust convection for locations near and west of I-75.
However, light rain ahead of that portion of the line may dampen
the severe potential even there. At any rate, once the QLCS clears
the JKL CWA after 12z, isolated to widely scattered convection is
possible this afternoon with the combination of daytime heating,
another passing subtle perturbation aloft, and a weak cold front
sagging in from the north. Today's forecast highs are in the mid
80s to around 90, though the humidity will make it feel more like
95 to 100 for most locations. Some of the CAMs suggest another
MCS forming this evening over southcentral Kentucky ahead of the
cold front and impacting portions of the Lake Cumberland area,
though confidence in this occurring is low. Additional
perturbations aloft may trigger another MCS riding the frontal
boundary overnight, but much of the guidance suggests that the
better parameter space will remain just to our southwest, thus the
MCS is more likely just to graze the Lake Cumberland vicinity
late in the night. Temperatures are forecast to bottom out in the
upper 60s to lower 70s.
Looking ahead to Wednesday, look for another day of similarly hot
temperatures with the highest heat and humidity near Lake Cumberland
where the cold frontal boundary will have stalled. Another MCS may
develop and track along the stalled boundary bringing another
opportunity for organized thunderstorms, best chances southwest of
US-421. In general this pattern will favor the potential for strong
to severe thunderstorms as each of these systems pass. The risk for
excessive rainfall is also greatest in those counties along and
southwest of US-421 where localized 36-hour amounts of 3 to 4 inches
cannot be ruled out, though amounts of 1/2 to 1 inch should be most
common.
.LONG TERM...(Thursday through Tuesday)
Issued at 408 PM EDT TUE JUL 30 2024
The beginning of the extended forecast period will be marked by the
building of shortwave 500mb ridging into the Ohio River Valley. With
flow in the bottom half of the atmospheric column out of the SW/WSW,
expect associated warm/moist air advection to pump afternoon highs
into the low/mid 90s and apparent temperatures to cross over the
triple digit threshold. Heat indices in some areas could approach
or even exceed 105 degrees on Thursday, and interests working
outside for extended periods of time should begin to review their
heat safety plans now to prepare for these elevated temperatures.
Amidst this shortwave ridging on Thursday, PoPs will be at a
relative minima compared to the previous and the following days,
although diurnally-driven convection is certainly still possible
amidst this thermodynamic profile.
Some forecast guidance resolves the progression of a MCS complex
across the northern portions of the CWA on Thursday, around the
periphery of the aforementioned upper level ridge. Amidst this
current pattern of progressive MCS-es, predecessor activity is
crucial in determining specifics. For now, the chances of this
happening are reflected in the PoPs as the highest chances being
in our northernmost and easternmost counties. A marginal (level
1/5) severe weather outlook from the Storm Prediction Center clips
the far northern portions of our CWA, but the greatest potential
currently exists further north into Indiana and Ohio. Mirroring
this, a marginal (level 1/5) risk for excessive rainfall covers
much of the forecast area, with Fleming County clipped by a slight
(level 2/5). Once again, the best chances for localized flooding
will be in any area (likely north) that feels the brunt of this
potential MCS and any backbuilding storms associated with it.
Adjustments to these outlooks and this specific forecast are
possible as the details surrounding this system are resolved in
higher resolution modeling, so interested parties should stay
tuned to future short term forecast issuances in the coming days.
Moving into the weekend, upper level troughing begins to dig into
the area, shifting flow to more southerly components and increasing
moisture throughout the column. As a result, expect cloud coverage
and rain chances to increase heading into the weekend again, and
high temperatures to decrease back into the mid/upper 80s in
response to this. Amidst this upper level flow, the passage of
shortwave disturbances will temporally enhance PoPs, although
nailing down the timing of these impulses at this range is
difficult. For now, kept a diurnal trend in the PoPs this weekend,
with peak coverage in the afternoon and evening hours.
After the aforementioned trough ejects into the Mid Atlantic states
on Sunday evening, longwave upper level ridging begins to build back
in from the Great Plains, bringing about much drier conditions with
it. Afternoon highs will thus creep back up into the 90s for the
start of the next work week and any rain chances will come from more
scattered/isolated pulse convection as upper level support retreats.
As a result, the risk of localized flooding should subside.
Overall, the end of the extended forecast appears to be in line
with classic early August weather in Eastern Kentucky: hot and
sunny.
&&
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 229 PM EDT TUE JUL 30 2024
At TAF issuance, MVFR was most prevalent in the southeast, while
mainly VFR was reported over the remainder of the area. Isolated
convection was occurring across eastern KY at this time, while
upstream of the region, an area of convection was approaching the
region from central and western KY. With destabilization occurring
ahead of the this convection, it should continue east southeast
and into eastern KY over the afternoon to early evening hours.
Confidence in thunder affecting the northeasternmost TAF sites of
KSYM, KJKL, and KSJS this afternoon to early this evening was too
low to include even a VCTS at this time. However, VCTS was
included at KSME and KLOZ over the first few hours of the period.
Additional convection may affect the region later this evening
into the overnight. A period of VCTS was included for that
potential at all sites. IFR or worse conditions will be possible
at any terminal which experiences a direct impact from a
thunderstorm. Winds could also be strong and erratic near
thunderstorms. Otherwise, winds will average southwest to west at
generally less than 10KT through 00Z and then southwest and then
be southwest at 5 to 10KT to end the period.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...JP
SHORT TERM...GEERTSON
LONG TERM...MARCUS/JP
AVIATION...JP
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 30, 5:18 PM EDT---------------
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