623
FXUS63 KJKL 071008
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
608 AM EDT Tue May 7 2024

.KEY MESSAGES...

- Our main shower and thunderstorm potential lasts into early
  Thursday, with a smaller possibility at times through the
  weekend.

- Severe thunderstorms are possible today through Wednesday night
  or Thursday morning. Large hail and damaging winds are the
  primary threats, but there is also a risk of tornadoes. Locally
  heavy rainfall could also lead to isolated flooding.

- Above normal temperatures are forecast through Thursday. A cold
  front should pass late in the week and turn temperatures below
  normal through the weekend.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 450 AM EDT TUE MAY 7 2024

Early this morning, an upper level low was centered over the Dakotas
with a broad trough across portions of the western and into the
Plains. A shortwave trough moving around the upper low was
nearing the mid MS Valley region with a couple of additional
weaker shortwaves also rotating around the upper low. At the
surface, occluded low pressure was centered over the Dakotas with
a triple point working across IA. A frontal zone extended east to
north of the OH River to the mid Atlantic coast with the trailing
cold front south and southwest to the Southern Plains.

Today, the shortwave trough nearing the mid MS Valley should
continue east an northeast across the Lower OH Valley region and
work into the Southern Great Lakes while the upper low meanders
over the Dakotas. The parent surface low should move little over
the Dakotas today with a triple point low developing over the
Great Lakes by this evening which should reach southern Ontario
by late tonight. The trailing cold front should approach the OH
Valley tonight. However, surface low pressure should begin to
evolve over the Plains on the southwestern extent of this boundary
as a more potent shortwave trough rotating around the upper level
move across the Four Corners region and into the Plains and
Central Conus on Wednesday. The frontal zone in the OH Valley
region should lift stall near the OH River while an outflow
boundary may linger near the KY and TN and KY and VA border
regions. This surface low should reach the mid MS Valley by
Wednesday evening. Periods of convection are expected during the
period with a warm and rather moist airmass in place. PW should be
in the 1 to 1.4 inch range today and much of tonight, though PW
should drop to 1 inch or less in the northern two thirds of the
area Wednesday morning to early Wednesday afternoon before
climbing back to 1 to 1.4 inch range to end the period.

Recent convective allowing models are generally consistent with 2-
5km updraft helicity probabilities from the 0Z HREF for where the
potential for severe weather later tonight and tonight is greatest.
These are greatest north of the Mtn Parkway and along the WV border
with the highest probabilities near and north of Interstate 64. 0Z
HREF 24 hour probabilities for today and tonight for wind are
generally greatest north of the Mountain Parkway and near the WV
border. Tornado and hail potential is greatest north and northwest
of the region where the strongest winds from a LLJ should be
present this afternoon and evening. SPC has the entire region in
a Slight Risk with the exception of portions of the far northwest
three counties which are in an Enhanced Risk for Day 1.

At this time it appears that there are two timeframe where severe
storms are most likely, the afternoon to early evening and again
overnight tonight. MUCAPE per the 0Z HREF mean should reach
generally the 1500 to 2500 J/kg range with bulk shear of 25 to
45KT though these values may climb toward 25 to 50KT by early
evening per forecast soundings in the north with effective shear
near 50KT. MLCAPE per the RAP should reach the 1500 to 2500 J/kg
range with pre convective low level lapse rates of 7 to 8 C/km
with mid level lapse rates more meager. Fixed layer STP may reach
1 to 2 if not a bit higher in the more northern and eastern
locations with 0-1 SRH of at least 100 to 150 m2/s2 per the 0Z
HREF with 0-3 SRH of at least 200 to 250 m2/s2. All indications
and CAM signals point toward the potential for a couple of
discrete cells with rotating updrafts and all three severe hazards
would likely coincide with peak heating, though wind and hail
would be possible overnight. Anywhere thunderstorms are
repetitious, heavy rain and isolated flash flooding would also be
a concern.

On Wednesday, a lull in shower and thunderstorm activity is
generally expected from the morning to midday behind an outflow
boundary that should reach near the VA and TN borders. However,
some recovery and instability should develop by the afternoon to
early evening, especially in the southwest, where MUCAPE should
climb toward 2000 J/kg per the 0Z HREF with 40 to 50KT of bulk
shear with effective shear values similar per the RAP. Late
Wednesday afternoon to early Wednesday evening mid level lapse
rates are likely to be at least marginally favorable for large
hail at 6.5 to 7C/km with low level lapse rates of at least 7C/km.
2-5km updraft helicity probabilities from the 0Z HREF are
greatest in the southwest portions of the CWA, generally after 19Z
or 3 PM EDT. Hodographs have some low level curvature and some
length in the southwest as well late in the afternoon and early in
the evening. 0-1 SRH Fixed layer STP values there are forecast in
the 1 to 2 range per the RAP late in the short term period. 0-1
SRH from the 0Z HREF mean climbs to 100 to 200 m2/s2 in the
southwest late in the period with 0-3 SRH climbing to at least 200
to 250 m2/s2. Supercells will again be possible, with perhaps a
tendency of more elevated storms further north from the TN and VA
borders and a better chance for surface based storms further
south. Either way, all hazards appear possible by late Wednesday
afternoon or early evening with the severe threat likely
increasings the long term period commences.

Temperatures will be mild with rather humid conditions in the short
term period with highs generally in the low to mid 80s both days
with mid 80s expected to more common on Wednesday. Lows tonight
should average in the mid to upper 60s.

.LONG TERM...(Wednesday night through Monday)
Issued at 441 AM EDT TUE MAY 7 2024

The most significant weather of the period is certainly front-
loaded, with a Day 2 enhanced svr tstm risk covering almost the
entire area which carries into Wednesday night. Mesoscale details
will be important for exactly how things pan out, and uncertainty
still exists in this regard. However, the larger picture does look
ominous. Surface low pressure tracking eastward across the Midwest
on Wednesday night will continue to pull warm and moist low level
air north northeast into the Ohio Valley. Combined with diurnal
heating, CAPE of 1500-3000 J/kg is expected to carry over into the
evening (where convection has not occurred and where it is able to
advect back into the area). Meanwhile, a positively tilted
mid/upper level trough will evolve over the Great Lakes and upper
Midwest and provide a veered, brisk west southwest flow of 50+ kts.
With ample shear and instability, severe wx should result. As
mentioned, the uncertainties involve where/when it occurs and
evolves. All severe hazards are on the table, including tornadoes,
especially if locally backed low level flow can occur due to
mesoscale features.

The main severe threat in the long term period is Wednesday
night, but thunderstorms could carry over into Thursday,
especially early in the day in southeast KY. Forecast soundings,
particularly in the NAM, also show a potential for redevelopment
in the afternoon. However, instability and forcing will be weaker,
with very dry mid-upper levels, which should keep activity more
benign and sparse. It will wane on Thursday night with loss of
heating and the arrival of significantly cooler and drier air.

The aforementioned mid/upper level trough will slowly shift
eastward with time. However, impulses rotating around the trough
will periodically enhance our shower potential through the
weekend. Forecast soundings suggest the thunder potential will be
fairly limited, with the best chance on Sunday afternoon, and a
slight chance of thunder has been included in our northeastern
counties then.

By Monday, the trough is lifting out to the northeast and our
geopotential heights are rising. With this we should have warming
temperatures and dry weather.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
ISSUED AT 250 AM EDT TUE MAY 7 2024

A general relative lull in the convection is expected tonight,
though activity should ramp back up by around 16Z though chances
should generally diminish from southwest to northeast toward 0Z.
Additional development over or upstream of the area is possible
near the end of the period as well. A round of strong to
potentially severe storms may affect portions of eastern Kentucky
between 17Z and 00Z, especially north of the Mtn Pkwy and nearer
to the WV border. Overall, with some clearing of low and mid
clouds having occurred following Monday`s convection a mixture of
valley fog and low stratus with some IFR ceilings or visibility
were occurring in some areas with MVFR or VFR ceilings in others.
In addition some isolated showers or a storm will occur over the
next few hours generally south of a SME to LOZ to I35 line. Most
locations should experience MVFR or IFR ceilings and or visibility
through 12Z or 13Z, before general improvements recovering to MVFR
and VFR through 18Z and generally VFR outside of showers and
storms thereafter. Winds will generally be out of the south to
southwest throughout the period generally at 10KT or less.
However, any showers or storms could lead to some higher gusts as
they move through. Some of the storms between 17Z and 24Z could
produce strong wind gusts, along with the potential for large hail
generally north of KSME, KLOZ, and KJKL though KSYM or KSJS
appear to have a better chance of being affected per recent
guidance and ensembles.

&&

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

$$

SHORT TERM...JP
LONG TERM...HAL
AVIATION...JP