-- Discussion containing changed information from previous version are highlighted. --
809
FXUS63 KJKL 072156 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
556 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.

&&

.SHORT TERM...
-- Changed Discussion --
(This evening through Wednesday night)
Issued at 431 PM EDT TUE MAY 7 2024

A warm front has lifted northward toward the Great Lakes and a
cold front is pushing into the Midwest this afternoon. We have
been watching a line of storms track across parts of the CWA all
afternoon. As these storms have slowly worked east, the effective
shear has been on the increase though the afternoon. This has led
to some isolated strong to severe storms this afternoon. Even so
these will quickly move east this afternoon and push into West
Virginia. The question that remains is how much if any additional
storms develop this afternoon. The CAMs so far have been quite
lack luster with additional storms including the HRRR. Even so,
this will have to be watched closely over the late afternoon and
evening hours, as effective shear of 50-60 knots is possible, but
instability is in question. Now the CAMs are in reasonable
alignment with a line of convection later tonight into Wednesday
morning. This is expected to move into the I-64 area around 05-06Z
and then moving into far southeast Kentucky around 11-12Z.
Confidence in severe weather will be a bit lower that late tonight
as we lose the better instability, but upper dynamics remain
stout.

Wednesday is much more interesting and concerning in terms of
severe weather potential. The previously mentioned line of
convection will settle across the TN Valley in the morning.
Meanwhile, a new low pressure will develop across the Plains and
push into the Middle Mississippi River Valley. This will help lift
a warm front north across the lower Ohio Valley. The question is
how far north does this warm front push. There is also indication
of a moisture boundary that pushes northward out of East and
Middle Tennessee as seen in the Theta-E fields. That being said,
several of the CAMs are highlighting the area of increasing
moisture pushing out of TN being a player for convection
Wednesday, with storm cells forming out ahead of a line of
convection. The environment is characterized by MLCAPE of
2000-3000 J/kg and effective shear of 40-50 knots. This would be
quite ample for rotating storms in the form of supercells. Now as
you move through the afternoon into the early evening the shear
increases, with effective SRH values increasing to 300-500 m2s-2.
Now the uncertainty remains with how this evolves, as early
morning convection will set the stage for the remainder of the
day. If storms can develop in this environmental space we could
see all hazards including large hail, severe winds gusts, and even
a few tornadoes. There is also this risk of flash flooding
Wednesday into Wednesday night. The issue with this is it will
take getting multiple rounds of convection given the antecedent
dry weather. By Wednesday night, the convection will dive
southward and eventually out of the area late Wednesday night.
This will lead to a decrease in severe weather risk, but some
isolated lingering flooding is not out of the question depending
on where the rain falls going through the day Wednesday.

.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.
-- End Changed Discussion --

&&

.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.
&&

$$

SHORT TERM...DJ
LONG TERM...HAL
AVIATION...DJ