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229
FXUS63 KJKL 220714
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
314 AM EDT Wed May 22 2024

.KEY MESSAGES...

- Dry weather is expected area wide through Wednesday morning.
  High temperatures may approach or exceed record levels this
  afternoon.

- There is a potential for showers and thunderstorms at times from
  Wednesday afternoon through Monday.

- Very warm temperatures will persist through Wednesday. An
  increase in clouds and the possibility of rain will bring
  somewhat lower temperature after that.

&&

.UPDATE...
Issued at 901 PM EDT TUE MAY 21 2024

Hourly grids were freshened up based on recent observations and
trends. The Afternoon convection diminished and a fresh ZFP was
sent accordingly. Some valley fog should again develop around or
shortly after midnight, with likely a bit less coverage compared
to last night as most locations remained rain free today.

&&

.SHORT TERM...
-- Changed Discussion --
(This evening through Wednesday night)
Issued at 308 PM EDT TUE MAY 21 2024

The afternoon surface analysis shows high pressure is posted up
along the Mid-Atlantic coast. Meanwhile, a low pressure and cold
front is pushing into the Midwest. In the mid-levels, a shortwave
trough axis is pushing eastward into the Midwest. We see subtle
mid-level height rises in the Lower Ohio Valley ahead of this
negatively tilting trough axis. This shortwave ridging will keep
our weather mostly quiet through the afternoon into tonight.
However, an isolated (chances of rain around 15-20 percent) shower
or thunderstorm remains possible through the afternoon before we
loose the diurnal heating and perhaps a weak shortwave noted
pushes east. After this, expect mostly clear skies to prevail
tonight, with some patchy to areas of fog mainly along the river
valleys late tonight into Wednesday morning.

Wednesday, the previously mentioned cold front will move eastward
toward the Ohio Valley late tonight into Wednesday. There is decent
agreement in the ensembles and deterministic guidance that
another low will develop along the weakening frontal boundary.
Particularly, as another shortwave is noted in the mid-levels
pushes east. However, the better height falls in the mid-levels
comes later in the day. Given the nearby cold front and some
shortwaves riding through the flow expect shower and thunderstorm
chances to increase through the day, with rain chances increasing
to 20-50 percent in the afternoon. SPC does have a risk of some
scattered severe weather for Wednesday, but overall the risk seems
low. However, if we can build some instability in the 1000-2000
J/kg of MUCAPE you would have decent kinematics to work with, as
effective shear climbs to around 30-40 knots. The best chance of
stronger storms would be generally along and north of the
Mountain Parkway. The main threat would be an isolated damaging
wind threat. We will not be as warm as the last few days owing to
cloud cover, with highs climbing into the lower to mid 80s in most
cases. Wednesday night, the diffuse cold front will stall out
nearby, with showers and thunderstorm chances continuing into the
night. Particularly given many of the CAMs, ensembles and
deterministic models show a shortwave trough riding through the
flow. This will lead rain chances around the 30-60 percent range.

.LONG TERM...(Thursday night through Tuesday)
Issued at 314 AM EDT WED MAY 22 2024

An unsettled long-term period is expected as active northern and
southern streams will push a train of shortwave disturbances east-
northeast across the Ohio and Tennessee River Valleys through
Sunday. From Monday onward, there is more uncertainty as the GFS and
ECMWF operational runs differ in placement of a large upper low in
proximity of the Great Lakes and southeastern Canada, especially as
it pertains to the strength, timing, and placement of shortwave
disturbances moving toward and through the Ohio Valley for the early
to middle part of next week.

While there is high confidence in the synoptic pattern, there is
practically no skill in accurately timing the shortwave disturbances
more than about 12 to 18 hours in advance, which means human
forecaster predicting hourly precipitation probabilities with high
skill is practically impossible. This is one of the primary reasons
the NBM was created, in order to synthesize dozens of ensemble
members into a calibrated consensus forecast that does show
considerably higher skill on average than a human forecaster. Have
thus used the NBM PoPs as-is for the duration of the long-term
period, with oscillations between chance (30 to 50 percent) and
categorical (75 to 100 percent) PoPs as the systems move across the
region in quick succession.

Above average temperatures can be expected from Thursday evening
through Monday as the region will mostly see light southerly winds
at the surface and west to southwest flow aloft. Clouds and periods
of precipitation will limit these warm anomalies to about 3 to 8
degrees above normal. Temperatures fall to near normal to slightly
below normal by Tuesday of next week as a cold front passes the
region and brings a more northerly component to the westerly flow,
especially aloft.
-- End Changed Discussion --

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 135 AM EDT WED MAY 22 2024

A challenging TAF forecast tonight, as uncertainty looms in the
latest model data. What is know is that a cold front will approach
the area from the northwest on Wednesday, and will eventually
stall out somewhere along the Ohio River. The coverage of showers
and storms we see today will depending largely on exactly where
the front sets up and activates. If the boundary moves further
southeast and sets up more directly over eastern Kentucky, the
TAF sites, and forecast area as a whole, will see more widespread
showers and storms. If, however, the boundary stalls out further
north and northwest, isolated to scattered activity is more likely
to occur. With so much uncertainty, decided to err on the side of
a little less shower and storm activity across our area today. We
will still see scattered showers and storms, and some of these
could at least move within the vicinity of any given airport, but
we will not go beyond that for now. Will continue to monitor
incoming model data and trends in the obs to determine if more
widespread rain should be forecast during the second half of the
TAF period. We should see southwest winds pick up late this
morning to around 10kts, with gusts of 15 to 20 kts possible at
times. SCT to BKN mid and high level clouds will stream in through
out the period, as cloud debris from approaching but decaying
thunderstorm cluster moves our way. It looks like, for now at
least that more widespread showers and storms may hold off until
near the end of the TAF period, as the cold front finally begins
to push our way again. In summary, VFR conditions should prevail,
but MVFR could occur if a shower or storm happens to directly
impact a TAF site.

&&

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

$$

UPDATE...JP
SHORT TERM...DJ
LONG TERM...CMC
AVIATION...AR