697
FXUS63 KJKL 220947
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
547 AM EDT Sat Jun 22 2024

.KEY MESSAGES...

- Hot and mainly dry weather will continue through the weekend.
  Afternoon heat indices will peak near 100 at some locations.

- The upper level high heights/ridge bringing our heat wave will
  weaken during the weekend and eventually allow a cold front to
  move into the area, with the PoPs peaking in the 50 to 70
  percent range from late Sunday afternoon and into the evening.

- Uncertainty still exists concerning the progress of the cold
  front next week and whether or not a substantially drier air
  mass will arrive. For this package, Monday night through Tuesday
  morning were left dry, but with precipitation and thunderstorm
  chances returning late Tuesday and continuing through Thursday.

&&

.UPDATE...
Issued at 205 AM EDT SAT JUN 22 2024

Blended the latest T/Td observations into the forecast grids to
freshen the nocturnal temperature trend. Otherwise, tonight`s
forecast remains on track.

UPDATE Issued at 1108 PM EDT FRI JUN 21 2024

Obs have been blended into the forecast without substantive
changes.

UPDATE Issued at 843 PM EDT FRI JUN 21 2024

Sprinkles have dried up and have timed out of the forecast. Have
made adjustments to the rate of temperature drop in valleys this
evening, with obs showing a more rapid fall in eastern valleys.

UPDATE Issued at 535 PM EDT FRI JUN 21 2024

Cu have built to the point that some light radar returns are
showing up in Bell and Harlan counties. Don`t think any place will
measure, but have added a chance of sprinkles early this evening.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 400 PM EDT FRI JUN 21 2024

19Z sfc analysis shows high pressure in place over eastern
Kentucky and this is keeping skies at least partly sunny with
light winds. Accordingly, temperatures have climbed to the upper
80s and lower 90s most places while, amid light winds, dewpoints
are running in the mid 60s. This is yielding heat indices in the
mid to upper 90s along with a tinge of haze in the air due to this
stagnant weather pattern. So far, no showers have been able to
develop across the higher terrain in the southeast parts of the
area, but this may yet happen though with minimal impacts and
a potential around 10 percent or less as subsidence and dry
conditions likely prevail.

The models, and their individual ensemble suites, remain in very
good agreement aloft through the short term portion of the
forecast. They all depict a dominant 5h ridge centered over
Kentucky today shifting southwest into Saturday. This will occur
as the mid level pattern to the north becomes more active through
the Great Lakes. The waves moving west to east at this level will
impinge deeper into the Ohio Valley later Saturday night with
some true 5h height falls working into Kentucky by dawn Sunday. As
this happens, the associated mid level energy will not be far off
in renewed northwest flow affecting eastern Kentucky early
Sunday. The model spread through the short term is still rather
small so the NBM was used as the starting point for the short term
grids with little deviation aside from the incorporation of some
terrain distinctions for temperatures tonight - and to a lesser
extent Saturday night. The latest CAMs runs were also incorporated
into the PoP grids for Saturday afternoon.

Sensible weather features the heat, humidity, and dry weather
continuing through the first part of the weekend. Look for just a
small chance for relief in the higher terrain of far southeast
Kentucky on Saturday afternoon in the form of spotty convection as
temperatures for the majority top out in the low 90s and heat
indices again threaten triple digits. Most places will stay dry,
though - awaiting a better chance starting Sunday when a much
anticipated (and needed) cold front slips into the area. Both the
upcoming nights will be very mild and muggy as mainly just the
valleys see lows in the mid to upper 60s by dawn Saturday - and
even fewer places end up on the cool side of 70 for Sunday
morning. Both nights mainly river valley fog will be noted.

The main changes to the NBM starting point consisted of adjusting
the temperatures in order to better reflect terrain details
tonight and a tad on Saturday night. PoPs were nudged up in the
higher southeast terrain on Saturday afternoon per the latest
guidance from the CAMS.

.LONG TERM...(Sunday night through Friday)
Issued at 547 AM EDT SAT JUN 22 2024

The upper level ridge will suppress southwestward during the
weekend, giving way to lowering heights across the Ohio Valley by
Sunday. This will be amplified by a shortwave turned upper level
low, which will move through the Upper Great Lakes Sunday afternoon
and night, then the Lower Great Lakes on Monday. A surface low will
be associated with this system, and will provide a cold front
stretching to the SW. The period will start off Sunday  night as the
front continues to sink southeastward through the JKL CWA. These
pops will linger in the far southeast part of the state through
Wednesday afternoon due to upslope flow, before finally departing.

By Monday night into Tuesday, the system will continue to exit to
the east, leaving KY in a brief area of high pressure at the
surface. Even so, with the latest NBM runs, it does try to put in
some isolated afternoon precip chances in the far SW CWA.
Unfortunately, in such a pattern without an upper level banked ridge
to keep it in place, these surface high pressure systems are short-
lived, as a shortwave begins to develop upstream in south-central
Canada by Tuesday morning. There is still some disagreement in the
models at this point, but they do at least both show precip along a
frontal boundary which will develop, connected to a surface low
pressure system co-located with the upper level low. While the ECMWF
doesn`t show precip from this system entering into KY until
Wednesday, the GFS brings two rounds, the first starting Tuesday
night. This seems to have been picked up by the NBM, which shows
slight chance pops overspreading the CWA Tuesday night. The rest of
the precip and frontal boundary should move through the state during
the day Wednesday. Will note that both the GFS and ECMWF also move a
secondary shortwave across Kentucky for Wednesday afternoon/night,
which will likely amplify the precip chances and QPF during this
time. This will be a slow moving system, so the front and lingering
precip could continue to impact the CWA through the day Thursday as
well before finally exiting to the east Thursday evening.

Surprisingly there is decent agreement at this point that another
round of surface high pressure may settle in across the Ohio Valley
for Friday, despite differing upper level solutions. As expected via
yesterday`s morning discussion, the slight chance pops were removed
by the NBM in the southern CWA. However, did note that the latest
ECMWF is snow trying to increase pops along the highest terrain now
Friday afternoon. We shall see if the NBM stays dry or if it trends
back towards isolated pops.

This high pressure will hold into the first part of Saturday, before
the next frontal boundary moves toward the state late in the day.

As for temperatures... This last week has been pretty stagnant,
temperatures in the 90s and humidity making it feel even hotter.
When we transition out of the ridging pattern, this also opens us up
to more temperature fluctuations. As frontal systems near, this will
increase SW flow across the state, providing warmer temperatures and
higher humidity. However, conversely, once the frontal system passes
through, this will bring some cooling NW flow to the region, albeit
even if it`s a few degrees and lower humidity. Tuesday is currently
the hottest forecasted day in the extended, as high pressure settles
overhead for much of the day giving maximum radiational heating,
despite having followed a cold frontal passage. Temperatures may
easily reach the low to mid 90s in many locations. Added humidity
will make it feel several degrees warmer than it already is,
reaching the upper 90s for many. The coolest day of the forecast
period is currently Thursday, behind the departing cold front and
with sharper height drops (per the ECMWF) allowing cooler air to
advect in from the NW. Either way, it`s late June...as long as the
sun is shining, it`s likely going to be a warm one. Even with the
cool down, temps will still top out in the mid and upper 80s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 158 AM EDT SAT JUN 22 2024

Valley fog will affect the region with IFR or worse conditions
through sunrise, but should avoid TAF sites. A few showers or
thunderstorms with sub-VFR conditions are possible in far
southeast KY this afternoon. Otherwise, VFR conditions are
expected through the period, with light and variable winds.

&&

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

$$

UPDATE...GEERTSON
SHORT TERM...GREIF
LONG TERM...JMW
AVIATION...GEERTSON