Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 161818
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
218 PM EDT Wed Aug 16 2017

.UPDATE...
Issued at 218 PM EDT WED AUG 16 2017

Showers continue to expand, especially near the I-75 corridor. We
have also see scattered showers develop across northeast Kentucky.
All of this activity will continue to push east and slowly weaken
later this evening. Locally heavy rainfall is possible with these
showers with very moist low levels in place with a very high
freezing level. Updated pops/weather to reflect the latest trends.

UPDATE Issued at 1033 AM EDT WED AUG 16 2017

Fog has pretty much lifted now across the area. Previous shower
activity has weakened as it pushed east, but a complex of heavier
rain is moving northeast across northern Russell county and
southern Casey county. This activity will likely continue to
intensify and expand as instability starts to build as skies clear
out after the morning fog/stratus. We have already begun to see
this intensification. Locally heavy rain will be possible.

UPDATE Issued at 908 AM EDT WED AUG 16 2017

GOES-16 visible imagery this morning still showing lots of fog
across eastern Kentucky, with only a slight dissipation in the
last 30 minutes. Thus, will keep the fog mention going for at
least another hour. A few showers are working across our southwest
zones and should continue to push east and north through the
morning. Very light rain is expected from this activity. Updated
grids to account for this shower activity. Showers will gradually
expand in coverage through the day as some isentropic ascent
builds across the area with the warm front as it starts to lift
northward.

UPDATE Issued at 730 AM EDT WED AUG 16 2017

Did a quick update to touch up the Sky, PoP, T, and Td grids per
the current conditions and trends as well as latest guidance from
the HRRR. Areas of dense fog persist, especially in the valleys.
These grids have been sent to the NDFD and web servers.

&&

.SHORT TERM...(Today through Thursday)
Issued at 415 AM EDT WED AUG 16 2017

07z sfc analysis shows a broad area of low pressure over the
region. Earlier in the night scattered showers faded out through
eastern Kentucky while the skies cleared. This has allowed for
areas of fog to develop throughout the CWA with some locally dense
patches found in the valleys. Currently, temperatures are running
in the low 70s on ridges to the upper 60s in the valleys while
dewpoints generally within a degree or two of the dry bulb with
the winds light to calm throughout the area.

The models are in good agreement aloft through the short term
portion of the forecast. They depict a building ridge over the
southeast portion of the nation while zonal to southwest flow is
found through the Ohio Valley north of this ridge. Within this
flow some weak packets of energy will pass through Kentucky today
before attention turns to a stronger shortwave trough moving into
the Upper Midwest by Thursday morning and then lifting northeast
into the Great Lakes by evening with height falls spreading
through the area late in the short term. Given the model
similarities have favored a general blend with wx specifics
derived mainly from the higher resolution HRRR and NAM12.

Sensible weather will feature fog burning off this morning with
partly sunny skies and warm conditions leading to scattered
showers and thunderstorms developing by early afternoon. Again,
any storms this afternoon could be prolific rain producers given
the high PW air. The convection will die off in the evening
setting the stage for a similar night of fog formation and ridge
to valley temperature differences. For Thursday, showers and
thunderstorms are again expected to develop this time out ahead of
an approaching cold front. A few of these storms could be strong
and potentially organized owing to good instability developing as
the day wears on, along with favorable mid and upper level winds.
Currently a good portion of our CWA is outlined for a marginal
risk of severe thunderstorms from SPC. Additionally, the storms
on Thursday should be more progressive and limit our concerns for
excessive rainfall, despite the still high PW air.

Again used the CONSShort as the starting point for the grids
through the short term portion of the forecast with some
adjustments to temperatures each night for terrain differences.
As for PoPs, did again enhance them diurnally and also broaden the
area of best chances on Thursday given some uncertainly remains.

.LONG TERM...(Thursday night through Tuesday)
Issued at 322 AM EDT WED AUG 16 2017

The extended portion of the forecast begins on Thursday night with
an active upper level pattern continuing. During the beginning of
the extended, a strong upper level low will be passing through
the OH Valley Thursday night as a surface cold front passes
through. Lingering convection will keep showers and thunderstorms
over the area through the night and into the day on Friday.
Forcing and instability in place should be enough to keep the
chance for precip through the night. Models suggest the front
moving through by Friday afternoon with precip coming to an end.

Surface high pressure moving in behind the front should keep mainly
dry conditions through the weekend. A weak disturbance passing by
to the north on Saturday evening may be enough to kick off a few
showers or storms north of the Mountain Parkway. Otherwise, a dry
weekend will be on tap.

By Monday, the mid level ridge over the southeast CONUS will
reengage the return flow into the southern and central Appalachian
with plenty or moisture brought into place. This setup with
another strong wave moving into the OH Valley by Monday afternoon
will set the stage for another bout of showers and thunderstorms.
Tuesday then follows with a continued active pattern as another
front shifts into the region with renewed convection lasting
through the end of the extended. The super blend adds some
confidence to this assessment as well. Overall, an active and wet
extended pattern will be in place.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 218 PM EDT WED AUG 16 2017

Scattered showers will be seen through the afternoon and early
evening hours and could bring some brief reductions in visibility
with the heavier downpours. Otherwise, VFR conditions are expected
through this evening. A warm front lifting north across the area
could bring some lower ceilings late tonight into early Thursday
morning, but confidence is low on whether ceilings or fog will
dominate. Either way, looking at some aviation concerns late
tonight again.

&&

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

$$

UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...SHALLENBERGER
AVIATION...KAS



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