513
FXUS63 KJKL 071747
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
147 PM 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.

&&

.UPDATE...
Issued at 1246 PM EDT TUE MAY 7 2024

We have a line and showers and thunderstorms moving through this
afternoon. These have been mostly benign, as better instability
and shear will trail the early afternoon convection. Not much was
changed grid wise for this update, but did opt to lower afternoon
highs a couple of degrees given the cloud cover and convection.

UPDATE Issued at 1052 AM EDT TUE MAY 7 2024

This morning monitoring upstream radars and a line of convection
continues to track eastward across western Kentucky and moving
into part of central Kentucky. So far, this activity has been
sub-severe and will set the stage for how activity develops this
afternoon and evening. Biggest change this update was to increase
PoPs with decent agreement on this line of convection pushing
across much of the area this afternoon. This warrants at least
60-80 PoPs through the afternoon. Outside of this, we are
continuing to monitor the potential for severe weather this
afternoon. The better parameter space is more northwest of the
area today, but a few strong to severe storms can`t be ruled out.
However, we will need to see how much recovery we see after this
morning convection moves through. This as strong shear moves in,
with effective shear this afternoon around 40-50 knots and
potential for MUCAPE values increasing into the 2000-3000 J/kg
range. This would be enough to organize a few storms if the
instability can increase this afternoon.

UPDATE Issued at 655 AM EDT TUE MAY 7 2024

Minor adjustments were made based on recent observations and
satellite trends. This generally led to lower visibilities and
greater coverage of fog initially in the southwest and less
coverage/lighter fog in the east under more cloud cover.

&&

.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 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 147 PM EDT TUE MAY 7 2024

We are seeing a mix of VFR and MVFR to begin the TAF period. We
are watching a line of convection push eastward across eastern
Kentucky this afternoon. These have or will track across the TAF
sites this afternoon. While these will be fairly docile, a few of
these could have some brief gusty winds. They could also lead to
brief lowering of CIGs and Vis. These will push through and we
could see a few more isolated to scattered storms develop later
this afternoon depending on recovery from this round. Then, late
tonight into Wednesday morning, much of the short term guidance
has another round of convection diving southward across the area.
This could lead to another period of showers and thunderstorms at
the TAF sites. This could also lead to another period of lower
CIGs and Vis, but still lots of questions on how this will evolve.
Then we should see yet another lull in activity through the
morning and early afternoon. However, fair amount of uncertainty
on when and how this activity evolves. Overall the winds will
remain out of the south and southwest at 10 knots or less, but
some brief gustier winds are always possible with thunderstorm
activity.

&&

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

$$

UPDATE...DJ
SHORT TERM...JP
LONG TERM...HAL
AVIATION...DJ