Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 191556 AAB
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1156 AM EDT Wed Jul 19 2017

.UPDATE...
Issued at 1155 AM EDT WED JUL 19 2017

Valley fog has long since dissipated with mainly fair weather cu
developing. Surface high pressure is centered over the
Appalachians with light southerly to westerly low level flow
leading to an increase in low level moisture. In general mid level
height rises are anticipated while a dampening shortwave moving
around the ridge should pass southwest of the area. Other than
deferential heating, there is not many triggers for deep
convection today and subsidence/warming between 850 mb and 700 mb
should keep cumulus shallow in most locations. The last couple of
HRRR runs do not develop convection over the area today, while 0Z
ARW and NMM runs developed isolated activity. The Rap keeps any
convection closer to the dampening shortwave over parts of central
KY. Coverage should be very meager, but opted to keep slight
chance pops for areas near the VA border from far southwest Pike
County/Jenkins vicinity southwest to Bell County. Temperatures
were running a tad above forecast in a few locations such as JKL
and based on COOP obs from Monday, opted to raise temperatures in
some valley and normally warmer locations a degree or two in the
the lower 90s. Overall, though, no substantial changes were made
to the forecast.

UPDATE Issued at 631 AM EDT WED JUL 19 2017

Mild and quiet this morning so far. Do have a layer of SCT to BKN
clouds around 4k feet moving through the western and northern
portion of the CWA, but seem to be showing a bit of a dissipating
trend. Updated cloud cover to account for these clouds over the
next few hours, though they are not expected to have any impacts.
Fog is being observed in the valleys, but almost all obs are
coming in at MVFR. One ob in the higher terrain is coming in at
3/4 mile, which is probably realistic for several of the deeper
valleys across eastern KY. This fog will continue to lift and
dissipate over the next couple of hours. Made a few tweaks to the
near term forecast for temps, dew points, and winds, to make sure
they were on track with current conditions. Also adjusted the
diurnal cure throughout the the morning a bit, to better capture
the increasing temperatures throughout the morning. All changes
have been published and sent to NDFD/web.

&&

.SHORT TERM...(Today through Thursday)
Issued at 355 AM EDT WED JUL 19 2017

Not many changes to the short term period to pass along. Strong
upper level ridging will continue to push its way eastward into
Kentucky during the day, while a shortwave/closed low just to our
east is pushed towards the Atlantic Coast. By Thursday, this ridge
will take full grasp of Kentucky with continued height increases,
while the closed low drops southward along the SE Atlantic coast,
heading towards Florida.

While high pressure should be in control at the surface across the
CWA, can`t rule out a stray shower/thunderstorm once more along
the VA border due to the close proximity to the upper level
disturbance. This feature has moved farther east than yesterday,
so don`t expect nearly the amount of coverage. In fact, only
mentioned slight chance pops for a few hours during the peak
afternoon heating just along the state line. Meanwhile, mostly
clear skies and building heights will translate to yet another hot
day across eastern KY. High temperatures will top the upper 80s
to around 90. Heat indices will be in the low 90s, which isn`t bad
considering, thanks to the fact that main flow will be out of the
NW and N, and not a more moist southerly flow which would have
resulted in much higher humidity and heat indices.

Overnight tonight, expect much of the same as previous nights,
with strong subsidence combining with mostly clear conditions and
light winds creating a good environment for fog development in
the valleys. As we lack moisture, expect impacts from this fog to
continue the improving trend from previous nights. However, near
rivers and bodies of water, can`t rule out some locally dense
spots.

For Thursday, the upper level ridge will be in full swing with no
remaining influence from the shortwave/closed low as it dives
south. High pressure at the surface continue to move across the
region as well. All in all it looks to be a mostly clear quiet day
once again across the entire CWA. Temperatures will be at their
warmest, however, hitting or topping 90 degrees in most locations.
Of more concern will be the heat indices, as it may reach the
upper 90s to near 100 across the western portion of the CWA, and
mid 90s elsewhere.

.LONG TERM...(Thursday night through Tuesday)
Issued at 409 AM EDT WED JUL 19 2017

We will initially be on the periphery of a strong mid/upper level
ridge over the south central CONUS, with surface high pressure
over our area. Ridging at the surface and aloft should break down
Friday through the weekend. In the upper levels, this will allow
for slight cooling and a modest increase in wind as the westerlies
drop further south. At the surface, increased flow will help to
bring Gulf of Mexico moisture into the area. The combined result
will be an overall increase in shower/thunderstorm coverage as we
move through the weekend. A cold front is expected to approach
from the northwest Sunday and Monday, and this is when the highest
POP will be carried. The GFS and ECMWF agree on the front passing
through from northwest to southeast late Monday and Monday night,
allowing for somewhat cooler and less humid air to move in. Until
then, conditions will be uncomfortably hot and humid. The highest
temperatures are expected on Friday, before the increase in
clouds and precip starts to hold temperatures down.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
ISSUED AT 639 AM EDT WED JUL 19 2017

Surface high pressure and an upper level ridge building into the
area will continue the rather stagnant weather pattern, with VFR
conditions and light winds prevailing once again throughout today
and into the overnight. Fog lifting out of the valley will
continue to impact SME off and on through 13Z, clearing out by
14Z. This afternoon, expect a FEW to SCT fair weather CU deck to
form around 3500ft. This will dissipate as we head into the
evening. Fog will develop in the river valleys once again late
tonight and into the dawn hours Thursday. Impacts will generally
be MVFR, but some of the deeper valleys and near bodies of water
could be lower. TAF sites should remain VFR and unaffected by the
fog.

&&

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

$$

UPDATE...JP
SHORT TERM...JMW
LONG TERM...HAL
AVIATION...JMW



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