Area Forecast Discussion
Issued by NWS Jackson, KY

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404
FXUS63 KJKL 170820
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
420 AM EDT Thu Aug 17 2017

.SHORT TERM...(Today through Friday)
Issued at 420 AM EDT THU AUG 17 2017

07z sfc analysis shows a developing warm front lifting northeast
through Kentucky. This is associated with a fairly strong area of
low pressure over the Upper Midwest. A local area of higher
pressure in the midst of these features has allowed for another
night of partly to mostly clear skies resulting in a small ridge
to valley temperature split as well as dense fog formation in the
deeper river valleys. The high dewpoints are limiting the
temperature fall this night with both not far from the low 70s
most places, though valleys are in the upper 60s. Winds are light
to calm with some patchy light fog outside of the valleys, as
well.

The models are in pretty good agreement aloft through the short
term portion of the forecast. They all depict a fairly strong
shortwave trough moving from the Upper Midwest into the Great
Lakes. As this happens, height falls will pass through the Ohio
Valley today along with some mid level energy riding through the
base of the trough. The trough`s influence and its lower heights
continue to press south into Kentucky on Friday as another cluster
of shortwave energy/troughiness reinforces the main pattern. Given
the decent model agreement will favor a general blend, though with
a strong lean toward the higher resolution HRRR and NAM12 for
weather details.

Sensible weather will feature fog burning off by mid morning in
the river valleys and elsewhere. Scattered showers and
thunderstorms in the morning should develop and increase in
coverage in the afternoon in the east as a lull sets up to the
west ahead of the system`s cold front. This front goes through
later in the evening and through the overnight with the best
chances for showers and storms. Any storm during the afternoon and
evening could become strong owing to good instability and
favorable winds aloft. The main threat from these will be gusty
and potentially damaging winds and SPC has outlined the northern
portion of the CWA in a marginal risk for severe weather today.
Have highlighted this in the HWO along with a mention of brief
heavy rain supported by high PW air but limited by better storm
motion than the past few days. The convection will end from
northwest to southeast early Friday as the front departs. Drier
air then spreads into the region providing relief by late
afternoon from the high humidity of late.

Once again the CONSShort was used as the starting point for the
grids through the short term portion of the forecast with some
adjustments to temperatures each night for terrain distinction.
As for PoPs, mainly spread them out a bit further than initially
populated for today and this evening as their remains some
uncertainly to the timing and extent of the frontal convection.

.LONG TERM...(Friday night through Wednesday)
Issued at 250 AM EDT THU AUG 17 2017

The extended portion of the forecast begins Friday night with a
continued active pattern in place. To start the period, an upper
level shortwave ridge will be passing over the area as a mainly dry
weekend will be on tap for eastern Kentucky. The one exception
will be over northeastern KY when the eastern CONUS will continue
to be under a lingering longwave trough. Thus another weak wave
will follow in behind Friday`s exiting front providing a small
chance of precip over the northern half of the forecast area for
Saturday afternoon. High pressure will keep the area dry for
Sunday. In fact, models suggest that the bubble will linger into
Monday keeping the area dry another day, at least in far eastern
Kentucky as the return flow will eek a bit of moisture into the
I-75 corridor area. Still only a slight chance of precip is
possible over the northern portion of the forecast area.

By Tuesday morning, combined with return flow advecting ample
moisture into the OH Valley and TN Valley, a strong cold front
will move into the region creating a prolonged period of showers
and thunderstorms Tuesday through Wednesday. The heavier activity
will coincide with the max heat of the day on Tuesday as it seems
PWATS will range between 1.75 and 1.90 during this period. Ample
moisture in place during this prolonged period may be enough for a
few minor flooding problems for early Tuesday through Wednesday
afternoon.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 155 AM EDT THU AUG 17 2017

The TAF period starts out with mostly clear to partly cloudy
skies. Expect a period of MVFR vis from fog at most sites in the
predawn hours with a potential for dense fog and VLIFR conditions.
Have included this in the lower elevations TAFs as a tempo. The
cloud cover will then gradually increase throughout the day,
Thursday, as an area of low pressure and its associated surface
cold front approach from the west. By late afternoon SYM and SME
can expected numerous showers and scattered thunderstorms, as the
cold front begins to move across the area. JKL, LOZ, and SJS
should see the best convective threat a bit later. Winds will be
generally out of the southwest at 5 to 8 KTs during the day,
otherwise light.

&&

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

$$

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



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