Area Forecast Discussion
Issued by NWS Jackson, KY

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269
FXUS63 KJKL 151200 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
800 AM EDT Tue Aug 15 2017

.UPDATE...
Issued at 800 AM EDT TUE AUG 15 2017

Did a quick update to touch up the PoP and Wx grids per the latest
radar trends and the most recent HRRR guidance. Also tweaked the T
and Td grids to account for the current obs. These grids have been
sent to the NDFD and web servers.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 410 AM EDT TUE AUG 15 2017

07z sfc analysis shows general low pressure through the area with
high dewpoint air in place. This is prompting light to moderate
showers to traipse across eastern Kentucky this night as well as
encouraging the development of fog despite the cloudy conditions.
Winds are light with temperatures fairly uniform in the lower 70s
most places along with dewpoints in the upper 60s to lower 70s.

The models are in good agreement with the long wave pattern over
the area through the short term portion of the forecast. They all
depict slight troughing in place along with broad southwest flow
through today with embedded shortwave impulses running nearly
zonal from west to east across Kentucky. Heights will be on a
slowly increasing trends ahead of the next main trough developing
over the Pacific Northwest and inland to the Northern Plains.
Given the model similarities and the small scale nature of the key
features for sensible weather will favor a general model blend
with a strong lean toward the HRRR and NAM12 for specifics.

No well defined boundary nearby and high pw air in place will keep
confidence rather low in timing and exact locations of the best
pcpn/heavy rain threats. Have hit the southeast section of the
area a little harder than the rest of the CWA per the guidance
agreement on this tendency - along with the best chance for heavy
rains there. The clouds and convection today will limit the warm
up, but low 80s are still expected. Drier air will settle into
this part of the state later today and overnight decreasing our
shower and thunderstorm chances, but not down to below 20% for
much of the area. High dewpoints tonight will mean a repeat with
mild temperatures, not much ridge to valley distinctions, and
more patchy/areas of non-terrain discriminating fog. The next
batch of rain should be moving into the area on Wednesday, as
similar conditions will be in place with some enhancement expected
from energy packets aloft.

Used the CONSShort as the starting point for the grids through the
short term portion of the forecast with only minor, point-based
adjustments to temperatures. As for PoPs, did enhance them
diurnally and kept them more focused in the southeast parts of
the area through Wednesday.

.LONG TERM...(Wednesday night through Monday)
Issued at 314 AM EDT TUE AUG 15 2017

The extended portion of the forecast begins on Wednesday night with
an active pattern on tap across the CONUS. The period will begin
with a strong trough tracking over the northern Plains and into
the Great Lakes as it drags a cold front over the OH Valley region
during the day on Thursday. Model profiles for Thursday afternoon
show quite a bit of instability and good directional shear. This
will definitely be a set up to monitor as SPC has issued a Day 3
Marginal severe risk. At this point, models so suggest that the
bulk of the dynamics and instability will be north of the Ohio
River where the greater risk will likely be.

Thursday night and into the weekend, the mid level ridge will set
up again over the Southeastern CONUS bringing return flow into the
area. This will be combined with several shortwaves passing
through the OH Valley with the next front passing through late
Saturday. At this time, this feature does not seem to have the
amount of instability and shear as the previous front. With the
return flow continuing into next week, the threat of afternoon
showers and thunderstorms will persist through the end of the
extended forecast period. Overall, a wet extended forecast is
expected through next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
ISSUED AT 745 AM EDT TUE AUG 15 2017

Scattered showers and a stray thunderstorm or two continue to
affect eastern Kentucky this morning. Coverage will be highest in
the south through the day. More instability around today will
likely result in additional thunderstorm development by
afternoon, but given uncertainty whether any particular TAF site
will be impacted, kept them with just VCTS, at this time. Winds
will remain light and variable throughout the period. Aside from
the storm threats for the afternoon, the main concern for this
TAF cycle is the ongoing flight categories due to fog and low
stratus clouds through mid morning. Conditions should begin
improving shortly by 14z, but expected no better than BKN cloud
cover in the low end VFR range through the afternoon with any
convection lowering the cigs/vis into the MVFR or lower range.
cigs should lift heading into the evening, but there is a
potential for more low cigs and fog later tonight.

&&

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

$$

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



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