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171
FXUS63 KJKL 300355 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1155 PM EDT Sat Jun 29 2024

.KEY MESSAGES...

- Thunderstorms are possible through Sunday as a cold front
  approaches and moves through. A few storms through the early
  overnight could produce strong wind gusts and heavy rain.

- A short-lived break from the heat and humidity is forecast on
  Monday behind the cold front, quickly followed by a return of
  sultry conditions.

- An active period of showers and thunderstorms may impact the
  Fourth of July holiday period from Wednesday through Friday.
  Best chances for showers and thunderstorms as of now are
  expected Thursday July 4th during the afternoon and evening.
  Heat indices will return to near 100 degrees for many locations
  as well during this time period.

&&

.UPDATE...
-- Changed Discussion --
Issued at 1155 PM EDT SAT JUN 29 2024

A cluster of showers with a few rumbles of thunder are dropping
south through the heart of the JKL CWA. Could still see some
additional showers and storms moving in from the northwest later
this night as the front creeps closer. Have updated the forecast
mainly to fine tune the PoPs through the rest of the night as well
as icluding the latest obs and trends for the T/Td/Sky grids. It
is worth noting that the low temperature for the date has been
only 76 degrees here at JKL so far and would set a monthly warm
minimum and tie the highest on record. However, an outflow and now
increasing rain chances through 1 am put all that in doubt.
Anyways, the updated grids have been sent to the NDFD and web
servers along with a freshening of the zones, HWO, and SAFs.

UPDATE Issued at 645 PM EDT SAT JUN 29 2024

22Z sfc analysis shows low pressure off to the northwest of the
area. This placed eastern Kentucky in a large warm sector out
ahead of a slow approaching cold front. For the most part, this
area has been capped at mid levels limiting the extent of any
convection despite high levels of instability. To the north,
closer to the better mid level flow, larger storms clusters - some
strong to severe - are moving just south of east. These may yet
threaten at least the northern parts of the JKL CWA later this
evening per trends and the latest CAMs. Should that occur, high
DCAPE and PWs could lead to damaging wind gusts and localized
flooding. Have updated the forecast with these ideas in mind and a
general timing for increased PoPs along and north of I-64 -
through midnight. Otherwise, its a very warm and humid start to
the evening with heat indices still around 100 degrees in many
locations - mostly owing to the high dewpoints. Specifically,
temperatures are running in the upper 80s to lower 90s while
dewpoints are in the low to mid 70s. Under partly sunny skies
winds are generally from the southwest to west at 5 to 10 mph. Did
also add in the latest obs and trends for the T/Td/Sky grids with
this update. These adjustments have been sent to the NDFD and web
servers along with a freshening of the zones and SAFs.
-- End Changed Discussion --

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 253 PM EDT SAT JUN 29 2024

A series of shortwaves will maintain a broader upper level trough
moving east across the Midwest, northeast CONUS, Ontario, and Quebec
this weekend. We are on the southern edge of the prevailing
westerlies aloft associated with the trough. The trough will support
a surface cold front which will approach tonight and then pass
through from northwest to southeast on Sunday. Low level southwest
flow ahead of the front has transported warm and humid air across
the region, with highs in the upper 80s to lower 90s and dew points
in the mid 70s, with heat indices in the upper 90s to lower 100s
this afternoon.

Forecast soundings indicate capping in the middle atmosphere this
afternoon as mid-level heights continue to rise, which has
seemingly thus far prevented anything more than spotty shower
activity. However, by mid-evening height falls occur as a strong
shortwave moves across the Great Lakes region, and all models
indicate the atmosphere becomes uncapped, with CAMS depicting one
of more thunderstorm clusters moving across the forecast area from
northwest to southeast, likely emanating from upstream
development. As for the severe threat, the 20 to 30 kts of shear
with moderate instability supports a Marginal Risk especially as
any potential MCS moves southeast into the forecast area primarily
this evening.

With expected shower and thunderstorm activity occurring mainly
this evening into the overnight, any rain followed by partial
clearing toward dawn will support fog development. Regardless,
expect warm and "soupy" conditions through the overnight with even
the valleys remaining at 70 degrees or higher.

The cold front will move southeast through the forecast area on
Sunday with a similar atmospheric set-up ahead of the front.
Southeast KY won`t have fropa until late Sunday and stands the best
shot at seeing more thunderstorms, while the far northwest part of
the forecast area is likely to have fropa before sufficient heating
to support development.

A much cooler and drier air mass moves into the region behind the
front, with temperatures falling into the mid 50s to lower 60s, with
warmer conditions in the valleys, especially if mixing from cool air
advection continues through the night.

.LONG TERM...(Monday through Saturday)
Issued at 315 PM EDT SAT JUN 29 2024

The various guidance including the ensembles are showing that a cold
front will push south of eastern Kentucky by early Monday. Then high
pressure builds into the Ohio Valley ushering in northeast flow
at the surface. This will aid in ushering in a much cooler and
drier airmass into the region. The airmass will be anomalous for
the first day of July, with PWATs running around 2 standard
deviations below normal and even some indication in ensembles we
could see near record min PWAT values for this time of year. The
afternoon highs will be running in the mid to upper 70s for most
locations and that around 5 to 10 degrees below climate normals.
These cool temperatures and decent afternoon mixing will set the
stage for a cool readings Monday night into Tuesday morning. That
said, lows in the low to mid 50s in the valleys and mid to upper
50s on the ridges under clear skies and good agreement on building
mid-level ridge for Monday night into Tuesday morning.

By Tuesday, there is good agreement on mid-level heights continue to
rise and high pressure pushes east allowing for some moisture
return. The cold front also pushes northward as a warm front Tuesday
afternoon. Even so, while warming into the upper 80s to lower 90s we
will see most locations see heat indices remain in the lower 90s.
This as moisture will lag behind some. However, ensembles and
deterministic guidance continue to build heights and moisture into
mid and late week timeframe. This will lead to warming, with
highs in the low to mid 90s by Wednesday and near 100 heat indices
possible at some locations. While most of Wednesday will be dry,
we could see some weakening in the ridging leading to the
potential for some shower and thunderstorm activity in the
afternoon (around a 15-30 percent chance of rain). The various
suites of guidance show this ridging breaks down further and we
become quasi-zonal mid-level flow across the Ohio Valley opening
up the potential for ridge riding mid-level waves. The NBM ramps
up chances of showers and thunderstorms to around the 60-70
percent range peaking Thursday afternoon. This seems reasonable
and some of these could be efficient precipitation producers given
the PWATs come back up closer to 2 inches or higher.

By the end of the week, there is some uncertainty on the
evolution of the waves mentioned before. However, given the ample
moisture and upstream cold front will stick with the NBM chances
of rain in the 60 percent range Friday. After this the models
really struggle with the passage of the previously mentioned cold
front and therefore keep Saturday chances of rain in the 30 to 50
percent range for now. However, could see this fluctuating before
that timeframe with some guidance suggesting it would be dry most
locations Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 715 PM EDT SAT JUN 29 2024

Showers and thunderstorms will likely impact the a few of the TAF
sites at times through the forecast period. The main window of
concern will be between 02 and 08Z with one or more thunderstorm
cluster depicted by high-resolution mesoscale models dropping into
the area. Meanwhile, until around 02Z, expect isolated showers
and thunderstorms. The spotty nature of this activity precludes
anything other than a mention of VCTS at this time. A few of the
storms later tonight could be strong to severe mainly producing
gusty winds. If a shower or thunderstorm impacts any TAF sites,
and there is any partial clearing by dawn, fog will likely crop up
at those terminals. Aside from fog and precipitation chances, VFR
conditions will hold for the majority of the time. Light
southwest winds of around 5 kts or less will continue into the
overnight hours, then become northwesterly later in the TAF
period. This will occur as a cold front brings much cooler and
drier air to this part of the state from northwest to southeast
during the day, Sunday - mostly after 18Z.

&&

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

$$

UPDATE...GREIF
SHORT TERM...CMC
LONG TERM...DJ
AVIATION...CMC/GREIF