-- Discussion containing changed information from previous version are highlighted. --
106
FXUS63 KJKL 111712
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
112 PM EDT Sat May 11 2024

.KEY MESSAGES...

- Some showers and perhaps a storm or two are possible, at times,
  this afternoon.

- Precipitation free weather is anticipated from Saturday night
  into Monday morning, before more unsettled weather returns.

- Expect rather cool temperatures through the weekend, with
  milder weather then returning.

&&

.UPDATE...
Issued at 1025 AM EDT SAT MAY 11 2024

Freshened up the forecast wording to remove morning fog potential.
Still look like a brief window for light rain showers this
morning, with a thunderstorm or two possible early this afternoon,
as another cold front moves through the region. Updated products
already out.

UPDATE Issued at 735 AM EDT SAT MAY 11 2024

A band of clouds at around 5k feet has been capping the growth of
the fog this morning leaving it more confined to the river
valleys. Will let the SPS run for this through 9 am. Have updated
the forecast mainly to add in the latest obs and trends for the
T/Td/Sky grids. These minor adjustments have been sent to the NDFD
and web servers.

&&

.SHORT TERM...(Today through Sunday)
Issued at 505 AM EDT SAT MAY 11 2024

08Z sfc analysis shows low pressure and a cold front approaching
the area from the northwest. Ahead of this, a bubble of high
pressure has been enough to keep the skies mostly clear and winds
light through the bulk of the night. As a result, fog formed
rather quickly in the valleys and has become thick. Now, a
smattering of low clouds is moving through the area during these
early morning hours and that should limit the expanse of the fog.
An SPS is in effect for most of the area for areas of dense valley
fog through 9 am. Otherwise, the conditions with this high has
allowed for a small ridge to valley difference to set up.
Specifically, readings vary from around 50 on the hilltops to
near 40 in the more sheltered spots of the east. Meanwhile,
dewpoints are within a degree or two of temperatures at most
observation sites.

The models, and their individual ensemble suites, are in excellent
agreement aloft through the short term portion of the forecast.
They all depict a clipper trough dropping into the Ohio Valley
this morning and passing by to the northeast of Kentucky through
the afternoon in northwest mid level flow. Slight 5h height falls
and a brush by of the shortwave`s energy will affect eastern
Kentucky into the evening. Heights will then slowly rebound
tonight with ridging starting to push into the region from the
west and practically overhead during the day, Sunday. The model
spread remains quite small with these key features so the NBM was
used as the starting point for the short term grids along with the
incorporation of the CAMs details for PoPs and timing through
this afternoon.

Sensible weather features another day on the cool side with a
passing threat for some showers as a result of an arriving cold
front. While showers will be the predominate form of precipitation
today - a few cells may find enough instability to break a cap
just above 700 mb and grow deep enough for some fleeting thunder,
although with rather small lapse rates. Just a small amount of
QPF is expected from the rainfall today - around a tenth of an
inch or less for most places. Post frontal, the convection pulls
out to east the tonight with clearing conditions and another bout
of ridge to valley temperature differences developing along with
some more limited valley fog as the winds stay up better than this
night. High pressure builds back into the area on Sunday
coincident with the rising heights of the upper level ridge. This
will mean a mostly sunny day with temperatures a notch warmer than
those of today - closer to normal in the mid 70s.

The main adjustments to the NBM starting point consisted of adding
in some terrain details to the hourly temperatures and lows
both this morning and again tonight. As for PoPs - the NBM values
were adjusted to include some CAMs details for the shower and
scant thunder chances through the afternoon hours with the passing
cold front.

.LONG TERM...(Sunday night through Friday)
Issued at 433 AM EDT SAT MAY 11 2024

Operational models are in good agreement through the first half
of the extended with synoptic features, and diverge from there. In
general, eastern Kentucky resides in a split flow pattern through
the period, with stronger wind fields (westerlies) across the
Deep South and to our north along the Northern Tier and Great
Lakes. Because of the weaker wind fields aloft, one main trough
only manages to crawl through the OH/TN valley regions from late
Monday through Wednesday. A second southern stream trough tracks
through the region late in the period, Dy7...or Friday. At the
surface, low pressure lifts out of the Great Plains and through
eastern Kentucky Tuesday into Wednesday, then a second low
pressure system moves into the TN valley by the end of the
forecast window.

Sensible weather features generally unsettled weather through the
extended with two main rounds of weather to deal with, the first
from late Monday through Wednesday, then a second round from
Thursday night through Friday. There are two periods of dry
weather, or at least a lull in shower activity, at the start of
the extended...Sunday night into Monday and then again Wednesday
night into Thursday. Due to a general lack of instability and
shear across the area through the period...and relatively weak
flow aloft, thunderstorm activity will likely be limited and occur
primarily during peak heating, or during the afternoon and early
evening time frame. Not seeing signals that would suggest much
hazardous weather through the period, though WPC does have eastern
Kentucky within a marginal risk for excessive rainfall Tuesday
and Tuesday night. Thinking is that this risk is primarily due to
the slow speed of the first system`s progression through the Ohio
and Tenn valleys. With limited instability and shear, and by
extension a lower risk of strong and/or severe thunderstorms over
our forecast area, it is difficult to see convection being a
primary ingredient to an overall hydro risk. Freezing levels are
not particularly high, generally below 11 kft through that portion
of the forecast. Wind fields are on the lighter side, but storm
motion is still greater than 10 kts until Tuesday night. By late
Tuesday night steering winds do drop to between 5-10 kts. PWATS
are up close to 1.4 inches, or 75th percentile of climatology.
Thus, while the threat of hydro issues is low at this time, it
would appear that if there were any problems, a Tuesday through
Tuesday night window of time would be most likely time frame of
concern.

&&

.AVIATION...
-- Changed Discussion --
(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 112 PM EDT SAT MAY 11 2024

Most active period this forecast cycle is in the first few hours,
with a band of clouds and associated showers progged to move
across the terminals this afternoon. Cannot rule out an isolated
tick of lightning, but not high enough confidence in any one site
to include in this set of TAFs. Winds will pick up from the west
and west northwest as well, with gusts of 15-20 kts. Winds will
die down quickly this evening with skies becoming partly cloudy to
clear.
-- End Changed Discussion --

&&

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

$$

UPDATE...SHARP/GREIF
SHORT TERM...GREIF
LONG TERM...RAY
AVIATION...SHARP