Area Forecast Discussion
Issued by NWS Nashville, TN

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909
FXUS64 KOHX 181052
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
452 AM CST Sat Nov 18 2017

.UPDATE...
FOR 12Z AVIATION DISCUSSION.

&&

.DISCUSSION...

Models have lined up a bit better in regards to precip timing
today, and have slowed down the arrival times slightly. Even
though the arrival times will be a bit later across the mid state,
the front still looks to move quickly across the area. Model
consensus has chances for showers and thunderstorms increasing
just after noon today in the northwest, mid afternoon for the I-65
corridor, and around or just before 6pm for the Plateau. Showers
look to be ongoing east of I-65 into the evening, but should be
confined to the Plateau around midnight and diminishing shortly
after.

Winds have not changed too much with models still indicating a
very tight pressure gradient and surface winds of 15-30 mph and
gusts to around 45 mph. South/southwesterly winds ahead of the
front will give way to northwest winds behind the front in the
late afternoon and evening from west to east, and initial
northwest winds behind the front will maintain the same strength.
With the later arrival times of the front across the area, decided
to have the entire region in a wind advisory until midnight as
models are showing criteria winds for most of the area after 9 pm
and before midnight. The western third of the mid state will
likely have winds drop below criteria around 9 pm, but with the
later trend of the front kept the whole area in the advisory
until midnight.

As for strong to severe storm chances today, models have
continued the upward trend in instability for the area, especially
in the northwest. The SPC has the far northwest part of the mid
state in a slight risk, with a marginal risk for the remainder of
the area. With very strong deep layer shear, and a bit more
instability compared to previous runs, theres potential for some
of the stronger storms to produce damaging winds ahead of the
front where forcing will be strongest. Depending on the location
and speed of the front, the threat for stronger storms may weaken
as the front progresses eastward across the region and loses some
of the diurnal support. Winds will remain strong, however, so
strong moisture advection in the low levels ahead of the front may
be enough to overcome the decreasing diurnal support, so kept in
mention of thunderstorms into the late afternoon and even early
evening over the Plateau region in case the front has a little
slower progression this evening. Also, with strong deep layer
shear, and strong low level shear, an isolated tornado or two can
not be ruled out. 0-1km shear vectors are showing 40-50 knots,
and is more than enough low level shear to help storm rotation.

Cloud cover still looks to linger on the Plateau a bit longer on
Sunday, but should clear out later in the afternoon and evening.
The drier trend looks to hold for next week with highs in the 50s.
Wednesday and Thursday may see highs in the 40s as a dry cold
front moves through the region thanks to a Midwest trough. The GFS
has the trough dig south and develop into a closed low over the
Gulf Coast, but the ECMWF does not. Either way, both models keep
the area dry. Next shot at rain looks to be late Saturday night
into Sunday morning as another Midwest trough brings a cold front
through the region.

&&

.AVIATION...
12Z TAF DISCUSSION.

CKV/BNA/MQY/CSV...Overall forecast reasoning not changed much from
06Z TAF issuance. Still will go with LLWS with 2 kft winds around
20050KT. Still looks like main time frame looks to be around 19Z
CKV, 20Z BNA/MQY, and 22Z CSV with this fast moving frontal
system. Frontal system should push east of mid state after 19/06Z
with sfc gusty winds continuing, but VFR thresholds being reached
as previous mainly MVFR ceilings erode.

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until midnight CST tonight for Bedford-Cannon-
Cheatham-Clay-Coffee-Cumberland-Davidson-De Kalb-Dickson-
Fentress-Giles-Grundy-Hickman-Houston-Humphreys-Jackson-Lawrence-
Lewis-Macon-Marshall-Maury-Montgomery-Overton-Perry-Pickett-
Putnam-Robertson-Rutherford-Smith-Stewart-Sumner-Trousdale-Van
Buren-Warren-Wayne-White-Williamson-Wilson.

&&

$$

DISCUSSION......Barnwell
AVIATION........31



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