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000
FXUS63 KJKL 060920
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
520 AM EDT Thu May 6 2021

.SHORT TERM...(Today through Friday)
Issued at 520 AM EDT THU MAY 6 2021

08Z sfc analysis shows high pressure building into eastern
Kentucky with light winds and clearing skies. This has resulted in
a small to moderate ridge to valley temperature split with the
dewpoint depression smallest in those eastern valleys where plenty
of ground moisture remains in place. As a result, areas of dense
fog formed along the rivers and expanded through the late night
hours. Have issued an SPS for this fog along with a social media
post. Otherwise, temperatures vary from the mid 40s on the ridges
to the upper 30s in many of the sheltered valleys. In addition to
the fog, cannot rule out a touch of frost this morning in a few
spots. Look for the fog to clear out after sunrise from northwest
to southeast with the last to dissipate toward 10 am nearer to the
Tennessee border.

The models are in very good agreement aloft through the short
term portion of the forecast. They all depict the further
deepening of the large eastern North American trough encompassing
the region through Friday. Heights bottom out over eastern
Kentucky tonight as another mid level wave moves through the base
of the trough with some attendant energy in northwest flow. Later
on Friday heights start to rebound locally, but additional
impulses will move over the JKL CWA in continued northwest flow.
Given the solid model agreement and small spread will favor the
blended NBM solution to start the grids with only minor
adjustments needed.

Sensible weather will feature another in a series of chillier
than normal days - following a cool and foggy start for many.
Midday sunshine will help temperatures rebound into the 60s for
most, but high clouds arriving later in the afternoon and westerly
winds will keep temperatures grounded. Later tonight, a secondary
cold front moves through the area with showers and a stray
thunderstorm possible. Temperatures will be more uniform during
this transition with lows generally in the lower 40s. For Friday,
steep lapse rates due to cold air aloft and some lift provided by
the core of the trough moving by will mean a good shot at some
low topped thunderstorms in the afternoon - also keeping
temperatures in check.

Only made minor tweaks to temperatures through the period from the
NBM considering the clouds and pcpn threats. As for those PoPs,
did mainly smooth and transition the better threat through the
area tonight while allowing for a rebound in the afternoon - well
after the front goes through.

.LONG TERM...(Friday night through Wednesday)
Issued at 520 AM EDT THU MAY 6 2021

Fairly active pattern throughout the extended, though there is quite
a bit of disagreement as well. This is already evident Friday night,
as an upper level wave begins to shift east of the state, and a
shortwave passes just to our NE. Each model puts a varying degree of
pops across the state and CWA throughout the overnight. Meanwhile,
the NBM goes dry for much of the overnight. Decided to keep the NBM
at this time, but if trends continue, expect there could be a chance
pops added during this time.

By Saturday, there is still agreement that a strong surface low will
form off the Rockies and make its way into the Central Plains. This
will create an increase of southerly flow on the eastward side of
this system, allowing for the development of a warm front draping
eastward from the low, across the Mid-Mississippi Valley and into
the Commonwealth. Generally scattered pops could start impacting
the CWA throughout the day, ramping up overnight as the low
pressure system continues to traverse eastward towards the Mid-
Mississippi Valley. The warm front will push just north of the
Ohio River by Sunday, with widespread pops expected across the
northern half of the CWA. While rain showers will be the main
mode, can`t rule out some scattered thunderstorms given the
boundary and lift in place. The center of the low should pass
eastward across the state or just north Sunday night, with an
associated cold front also passing through during the first part
of the day Monday. Widespread showers and a chance of
thunderstorms will continue during this time, peaking along the
cold front, then tapering off to chance pops Monday. Instability
will also cut off behind the front as cooler air moves in, so only
rain showers are expected by Monday. The ECMWF goes dry across
the CWA between 18 and 0Z, and the GFS is about 6+ hours slower.

Once this system exits, a very strong area of high pressure will
work in from our NW on Tuesday, amid continued, though weakening, NW
flow. With the latest models runs, there has been some agreement now
between the GFS and ECMWF, in that systems developing to our west
should be shunted SEward around this high, impacting locations to
our west and south, but keeping KY dry. Meanwhile, the NBM continued
to put chance pops across the entire CWA during this time, despite
the models being dry. Ended up dropping pops to below slight chances
from Monday night through Wednesday morning as a result.

Eventually the high will shift eastward and allow for return flow
into the region. A low pressure system and associated elongated
frontal boundary will be located along the Gulf Coast Wednesday,
with widespread precip expected across much of the Deep South. With
the return southerly flow, some of these pops may advect their way
northward and into the southern CWA by Wednesday afternoon according
to the ECWMF. These pops will continue across the CWA as the low
lifts northward toward across the southern Appalachians into
Thursday. Meanwhile, in the GFS world, KY should remain dry through
the day Wednesday. This model then has a upper level low developing
and moving towards the state Wednesday night into Thursday, along
with a developing surface low. This brings much more widespread pops
to the state from Wednesday night through the day Thursday as the
low passes through. Obviously, there is quite a bit of uncertainty
as to which model solution is correct. At this point, chose to keep
chances pops confined to more of the SE portion of the state and JKL
CWA during the day Wednesday, then kept with the NBM pops Wednesday
night through Thursday. At this time, the NBM is going chance pops,
but depending on which model solution is correct, this could either
increase or decrease in the coming model runs.

Temperatures are still slated to remain well below normal during the
entire period, given the continued NW flow aloft through much of the
week. Daytime highs will generally be in the 60s. Sunday remains our
warmest day, with southerly flow at the surface ramping up just
ahead of the incoming low pressure system. Even still, NW flow
aloft, plus abundant clouds and precip, will keep temps in the low
to mid 70s for most locations.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 230 AM EDT THU MAY 6 2021

Already a large amount of fog has formed in the valleys - likely
seeing widespread IFR or worse conditions by dawn. Have included
LIFR vis at SJS by around 10Z; however, conditions could worsen
more quickly. Have allowed for prevailing MVFR fog at KSME and
KLOZ, as these locations will be closer to the drier air advecting
into the area on light northwest winds, but also included a tempo
for SME down to IFR toward dawn. Will maintain VFR conditions at
KSYM and KJKL for now. Fog will burn off by around 13Z or so,
with increasing mid-level clouds during the day out ahead of an
approaching cold front. This will likely bring showers to the
areas tonight. Winds will generally be light and variable through
the bulk of the period, but peak near 10 kts from the west around
midday Thursday.

&&

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

$$

SHORT TERM...GREIF
LONG TERM...JMW
AVIATION...GEOGERIAN/GREIF