Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 210600 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
200 AM EDT Mon Aug 21 2017

.UPDATE...
Issued at 200 AM EDT MON AUG 21 2017

Lowered the temperatures in a few places based on the latest
trends in observations, otherwise the forecast remains on track.

UPDATE Issued at 813 PM EDT SUN AUG 20 2017

A few mid-high clouds will continue to stream in this evening as
decaying showers/storms push through the Midwest into the Ohio
Valley downstream of an upper wave swinging through the Corn Belt
and Great Lakes. Deep layer high pressure will hold supreme and
keep precipitation nil across eastern Kentucky.

Given the degree of mixing and drier air that materialized across
portions of the Cumberland Valley this afternoon, reduced fog
coverage outside of deeper river valleys where nocturnal drainage
will allow for development later tonight. More widespread valley
fog will be a better bet from the Bluegrass and Big Sandy regions
through the remainder of the higher terrain where greater surface
moisture and subsequently higher crossover temperatures reside.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 309 PM EDT SUN AUG 20 2017

Afternoon surface analysis shows an area of high pressure in SW PA
and warm front lifting north across the Ohio Valley. We will
remain under the control of rising heights and surface high
pressure. That said, we have CU developing across the region and
some higher level cirrus streaming by at times this afternoon.
These CU will dissipate tonight and we will see another night of
mostly clear skies. This will lead to the potential for more
patchy to areas of fog toward the overnight hours. This will
dissipate through the morning on Monday.

Monday will be a interesting day given the solar eclipse. There
remains some question on how much this will affect many things
such as clouds and temperatures. We will be watching how a MCS
develops across portions of the Midwest and this could certainly
send a few high clouds south. Another issue will be how much CU
develops before the eclipse, but still think there will be a few
despite the potential affects. However, do not think this will
lead to major issues for viewing the solar eclipse. Do think the
eclipse will lower temperatures around 18Z and then it should
warm up again following the eclipse. Did keep temperatures in the
upper 80s for most locations, as the recovery may be delayed
enough to impact peak heating.

After the eclipse all eyes do turn to the upper level trough
across the Upper Midwest. This will begin moving SE toward the
Ohio Valley. We will probably see some more clouds given this, but
do not think we will see any precipitation before the end of the
period. Overall limited the fog more so given the potential for
some cloud cover.

.LONG TERM...(Tuesday through Sunday)
Issued at 400 PM EDT SUN AUG 20 2017

The models are in fairly good agreement aloft through the
extended portion of the forecast. They all depict an amplifying
trough pushing through the Upper Midwest and into the Great Lakes
on Tuesday. This will spread lower heights south through the Ohio
Valley and into Kentucky along with a strand of mid level energy.
Heights will continue to fall through the day Wednesday as the
core of the trough pivots into eastern Canada leaving northwest
flow behind through the region and across Kentucky, though the
bulk of the energy will remain well to the north. The pattern
relaxes toward the end of the week with gradual height increases
and advection that is more neutral at mid levels. However, by the
latter part of the weekend, heights could be on their way back
down as a new trough enters the picture from the northwest with a
return of somewhat more substantial energy packets for the Ohio
Valley, though the ECMWF is an outlier with its further south
closed low for the Northern Plains. Given the model similarities
and only minor differences during the first part of extended
confidence initially is above average for the blended solution
with lower confidence for the upcoming weekend as the model spread
increases.

Sensible weather will feature a cold front pressing southeast
into the area as the main sfc low runs east into Quebec. This
boundary will drop through eastern Kentucky Tuesday night into
midday Wednesday as high pressure pushes in from the northwest.
This front will need to be watched for a potential of severe
weather owing to good instability Tuesday afternoon and evening as
well as favorable winds aloft. Additionally, training of storms
cells will be possible as the low level flow will be nearly
parallel to the sfc boundary. Otherwise, once the front goes
through cooler and less humid weather will follow through the bulk
of the week, though a lingering shower or storm cannot be ruled
out in the far southeast Wednesday afternoon and evening. Sfc high
pressure will slip east Saturday and Sunday with return flow
moisture and increasing heat leading to a potential for mainly
diurnally driven storms for the latter half of the weekend. A
stray convective cell cannot be ruled out on Saturday, but it
looks unlikely at this point.

Made only minor terrain based adjustments to the temperatures each
night under the expectation of ridge to valley differences for
most nights (aside from Tuesday night). As for PoPs - scaled them
down quicker on the backside of the front as it drops south of
the area on Wednesday. Also, held them back a tad on Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 200 AM EDT MON AUG 21 2017

IFR or worse fog will be seen in the deeper river valleys through
13z, before dissipating. This should generally avoid the TAF
sites, given the lower crossover temperatures from yesterday
afternoon. Some cumulus at 5-6k feet agl will develop during the
day, along with some passing high clouds. Winds will average less
than 5 kts through the period.

&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...DJ
LONG TERM...GREIF
AVIATION...GEOGERIAN



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