EF0 tornado, Yellow Creek, Tennessee, February 7, 2017

Area Forecast Discussion
National Weather Service Nashville TN
535 AM CST Tue Feb 7 2017

.UPDATE...
FOR 12Z AVIATION DISCUSSION.

&&

.DISCUSSION...

An interesting day is in store for us here in Middle Tennessee.
At forecast time, other than a few showers streaming across the
area, it's relatively quiet.  However, if we look upstream, the
action is already under way.  Showers and thunderstorms have already
crossed over the Mississippi River and are headed across West
Tennessee.  These storms will likely break into our northwest
counties over the next couple of hours and with little to no surface
based instability present, these storms should pass through Middle
Tennessee with little to no fanfare.  As we get into the daylight
hours, the activity that is further upstream (currently over
Arkansas) will start to near the mid-state and it's these storms
we'll have to start watching for the potential of severe weather.
Parsing the forecast soundings, not much has changed in regards
to our forecast thinking. There will be at least a marginal chance
for damaging straight line winds and hail, especially during the
morning hours. This is when the wind fields are their strongest. A
50-60 kt 850mb LLJ will provide 0-3km helicities potent enough to
help sustain updrafts. As we get into the afternoon hours, these
wind fields begin to weaken. That 850mb jet weakens to 30 kts and
while that's nothing to sneeze at with surface instability
climbing near 1000 J/Kg, it's not what it could be. So, as we get
into the afternoon, we'll start looking for much more isolated
instances of sustained updrafts. Latest HRRR suggests there's just
enough deep layer shear to organize a weak line as the bulk of
the precip pushes across I-65 early this afternoon. This is most
likely where the afternoon threat of severe weather will be
concentrated. Again, with surface winds out of the southwest, the
tornado threat will be low -- though not zero -- throughout this
event.

Outside of today's thunderstorms, it's going to be breezy.  Gusts of
30 to 35 mph will be possible until that LLJ weakens later this
afternoon.

As advertised, today's thunderstorms will be pre-frontal.  The
actual front still isn't expected to push through Middle Tennessee
until Wednesday afternoon.  This means that while we'll probably
have a decent lull in activity tonight, we could see some more
convective development on Wednesday just ahead of the front.
Instabilities will be lower than today, but there could be just
enough deep layer shear to organize some of this convection, so a
few strong storms will be possible late Wednesday morning into the
early afternoon hours, especially south of I-40.

Behind the front, some precipitation will linger into Wednesday
night. There's still plenty of model inconsistencies regarding
how quickly the cold air will push in behind the front. Because of
this, I'm still only going to carry a chance of some light snow
on the northern Plateau early Thursday morning. QPFs are still
very light, so this should be of little to no consequence.

We'll dry out starting Thursday.  Temperatures will be much more
seasonal, but this won't last long as the surface ridge following
tomorrow's frontal passage will get east of us quickly and provide
southerly flow as early as Friday. This will allow us to warm up
once again, with afternoon highs back into the upper 50s and 60s
Friday and Saturday. Another front is still progged to push
through Sunday, but the latest extended guidance has weakened this
front considerably. Because of this, I'm still only going to
carry a chance PoP for Sunday.

&&

.AVIATION...
12Z TAF DISCUSSION.

Showers and thunderstorms will move across the area today,
bringing MVFR/IFR conditions at times for all terminals. KCKV is
already seeing showers and thunderstorms this morning, and another
wave will come through this morning. Best thoughts on timing looks
to be now through 18Z for KCKV, around 15Z through 23Z for KBNA,
and 17Z through 00Z for KCSV. Some storms may be strong to severe,
with gusty winds and hail during those timeframes. Cigs look to
mainly be MVFR, but storms may drop cigs/vis to IFR at times.
Winds will be strong out of the SSW most of the day, and calming
down this evening, but looking at speeds of sustained around 10-15
knots and gusts from 15-25 knots this morning and afternoon. Put
in mention of wind shear at all terminals this morning due to the
strong LLJ ahead of the precipitation. Models want to keep cigs
VFR for KCKV this evening and overnight, and MVFR at KBNA.
However, KCSV looks to stay with IFR cigs and eventually LIFR
cigs, with indications of fog development overnight into Wednesday
morning. Put in mention of LIFR cigs and MVFR fog for now at KCSV
early Wednesday morning.

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

DISCUSSION......Unger
AVIATION........Barnwell

Hazardous Weather Outlook
National Weather Service Nashville TN
554 AM CST Tue Feb 7 2017

TNZ005>011-023>034-056>066-075-077>080-093>095-081200-
Stewart-Montgomery-Robertson-Sumner-Macon-Clay-Pickett-Houston-
Humphreys-Dickson-Cheatham-Davidson-Wilson-Trousdale-Smith-
Jackson-Putnam-Overton-Fentress-Perry-Hickman-Lewis-Williamson-
Maury-Marshall-Rutherford-Cannon-De Kalb-White-Cumberland-Bedford-
Coffee-Warren-Grundy-Van Buren-Wayne-Lawrence-Giles-
554 AM CST Tue Feb 7 2017

This Hazardous Weather Outlook is for portions of Middle
Tennessee.

.DAY ONE...Today and Tonight.

Strong to severe thunderstorms will be possible today across all
of Middle Tennessee. While the tornado threat will be low,
damaging straight line winds and large hail will be the main
threats. The main focus areas will be west of I-65 this morning
and east of I-65 this afternoon.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

A couple of strong storms will be possible during the late morning
and early afternoon hours Wednesday. Strong gusty winds and small
hail will be possible, especially south of I-40.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is requested today. Please report any storm
damage in Middle Tennessee to the National Weather Service in
Nashville.

THUNDERSTORM SPOTTER REPORTING CRITERIA...
Tornado
Funnel Cloud
Flooding
Hail >= 1/2 inch
Winds > 50 MPH (measured)
Structural Damage
Tress or Power Lines Down

27

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