Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 171806
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
206 PM EDT Wed Jul 17 2019

.UPDATE...
Issued at 1146 AM EDT WED JUL 17 2019

Shower activity remains progressive with rainfall amounts
generally remaining below 1/10 of an inch at any given location
at this time. Will see coverage of showers/storms increase this
afternoon with heating and upper wave moving through.

For Friday and Saturday, went ahead and expanded the Excessive
Heat Watch to encompass Powell, Estill, Rowan, and Elliott
Counties given continuing trends in heat indices exceeding 100 and
nearing 105 degrees.

UPDATE Issued at 657 AM EDT WED JUL 17 2019

A few showers have developed this morning and are progressing
across portions of the region this morning. We will see increasing
coverage of showers and eventually thunderstorms through the rest
of the morning and afternoon. Overall grids are in reasonable
shape with the trends and only updated for the latest obs.

&&

.SHORT TERM...(Today through Thursday)
Issued at 359 AM EDT WED JUL 17 2019

The morning surface analysis reveals low pressure across the Great
Lakes and high pressure to the east off the Atlantic coast. This
is leading to ample moisture advection across the Ohio Valley this
morning. Meanwhile in the upper levels, a trough axis was making
it into the Ohio Valley at 00Z. This is picking up what is left of
the tropical system formerly know as Barry and progressing it
east. This open wave and some low level jet influence will give
way to increased showers and thunderstorms across eastern Kentucky
through the morning and afternoon. There will be questions as to
the extent of the instability through the day, as GOES-16 data
shows clouds filling into the Tennessee Valley this morning and
this will advect northward today. Even with more instability the
effective shear will be nil leading unorganized convection. The
other question will be heavy rainfall given the PWAT values climb
to 2 inches or so through the late morning and early afternoon.
Again, while this deep tropical moisture will be in play, the
convection will have reasonable storm motions, and also most
areas have not been overly saturated heading into today. This
said, we should see more in the way of isolated concerns today and
WPC leaned this way with the latest day 1 excessive rainfall
outlook going marginal for eastern Kentucky. Therefore, will lean
away from a Flash Flood Watch for today.

This trough axis will progress east tonight and this will lead to
lesser convection through the evening. There is a hint of
possibly a inverted surface trough setting near Appalachia and
therefore kept some chance PoPs in the far east and southeast
tonight. After this, Thursday will see PoP trending down and
becoming more anchored to the higher terrain near the Tennessee
and Virginia border, as heights rise from the building upper level
ridging in the central part of the US. This will be the start of
hot weather heading into the end of the week, with highs topping
out in the upper 80s and heat indices in the low to mid 90s east
and mid to upper 90s moving toward the I-75 corridor.

.LONG TERM...(Thursday night through Tuesday)
Issued at 440 AM EDT WED JUL 17 2019

The models are in good agreement aloft through the majority of
extended portion of the forecast - at least through the first
part of the weekend - before differences start to magnify with a
trough digging into the Upper Midwest and Great Lakes region. They
all similarly depict the building ridge over the region from
Thursday night through Saturday. Heights will then start to back
off on Sunday in response to a pattern changing trough plowing
just south of east through the northern tier of the nation. The
influence of this trough and its attendant energy impulses will
further beat down the oppressive mid level ridge to close out the
weekend. The GFS has backed off its more extreme solution of a
nearly closed trough entering the states from 24 hours ago. As a
result, the main models are now in better agreement, though the
ECMWF remains flatter and quicker with this features. Regardless,
they do agree in the heights continuing to fall through the Ohio
Valley to start the new work week as a larger trough starts to
carve itself out over the north central and eastern portion of the
nation. Height falls will continue through the area into Tuesday
with additional energy passing through Kentucky that day as the
trough takes hold - still stronger in the GFS than the ECMWF.
Given the model agreement through the first part of the extended
and better matching later have again favored the model blend
represented by the NBM for starting the grids.

Sensible weather will feature heat and humidity building under
that strong dome of high heights and warm air aloft through
Saturday. This will not only send heat indices to above 100
degrees each afternoon for most, but also suppress convections in
all but the higher terrain along the Virginia and nearer the
Tennessee border. As a result, have issued an Excessive Heat
Watch for our Bluegrass counties northwest of I-64 where Heat
Index values will approach 105 degrees at times both Friday and
Saturday afternoon. The rest of the area was highlighted for the
heat by an SPS detailing the best times for Apparent T values near
or above 100 degrees. The heat will break most cleanly on Monday,
though Sunday should not be quite as bad with more clouds and
convection around. Monday will feature a frontal boundary settling
over the area with cooler temps and higher convection chances.
This boundary then slowly moves through the region keeping the
shower and storm chances in the picture through Tuesday - but
with less heat and humidity.

As for temperatures in the extended, did tweak the NBM lows for a
very small ridge to valley splits each night through Sunday
morning - still limited by the high dewpoints. For the PoPs and
QPF: mainly adhered to an enhanced diurnal component through
Sunday before allowing the frontal position to primarily drive
these grids.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 206 PM EDT WED JUL 17 2019

Showers will continue to accompany mainly MVFR ceilings through
mid afternoon. May make a run at low-end VFR criteria later this
afternoon into this evening, prior to falling back into the MVFR
realm later this evening into tonight with ample moisture in
place. Fog should be limited overnight by low clouds, but will
likely see patches of sub-VFR visibilities, especially underneath
rain showers. A few wind gusts of 15-20 knots from the
west/southwest will be possible this afternoon and early evening,
prior to winds decreasing to 5 knots or less overnight into
Thursday morning. Look for widespread rain to end overnight with
MVFR ceilings approaching IFR levels. These will be slow to
lift/mix out Thursday morning as west/southwest winds increase to
5-10 knots.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Friday afternoon through Saturday
evening for KYZ044-050>052-058-059-104.

&&

$$

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


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