Special Weather Statement, NWS Nashville, TN

Area Forecast Discussion
National Weather Service Nashville TN
513 AM CST Wed Mar 1 2017

.UPDATE...
FOR 12Z AVIATION DISCUSSION.

&&

.DISCUSSION...

Looking at present convection to our west and northwest, moving
into the mid MS Valley and stretching northeastward into the Ohio
River Valley Region, the 06Z NAM solution actually initializes
best, with the latest HRRR runs following close behind. Will thus
have a lean toward the NAM/HRRR solutions thru today. Overall,
model runs on the whole are much more in consensus than this time
yesterday morning though with the evolution of this strong sfc
cold frontal passage across our region today. Also, the passage
of this strong sfc cold front is slower than thought at this time
yesterday also across our region. Thus, this brings us to the
most pressing quandaries, i.e. when are those lines of shwrs/tstms
going to initially move into the mid state region, how is this
convection going to progress across the mid state region, when
should it exit the mid state region, and what impacts will it
bring.

In line with a 06Z NAM/HRRR lean, expect wrn portions of the mid
state to experience shwrs/tstms 01/13Z-01/16Z, central portions
01/15Z-01/18Z, and eastern portions 01/17Z-01/21Z. Latest NAM BNA
model sounding profile showing sfc based CAPE values surging to
around 1500 J/KG from around 01/15Z to around 01/18Z, 60kt+
850 mb low level jet dynamics across most of mid state becoming
established between 01/12Z-01/18Z, SRH values from sfc-1km, sfc-
2km, and sfc-3km in the 350m2/s2 to 450 m2/s2 range between
01/12Z-01/15Z, along with several other derived atm instability
and wind shear indices, pointing toward the unstableness of the
air mass across our region as the morning hrs progress and even
into the early afternoon hrs across eastern portions of the mid
state region including the Cumberland Plateau Region. Currently
temps just after 01/09Z are in the mid 60s to lower 70, with
dewpoints spanning the 60s, and southerly to southwesterly sfc
winds sustained 10 to 20 mph with gusts to around 35 mph. SPC has
placed the entire mid state in an enhanced risk from 01/12Z
onward. Damaging winds still look to be the main concern, although
the formation of a few tornadoes especially with any embedded or
discrete supercells, and large hail, along with brief heavy
downpours from the stronger tstms certainly could certainly occur
also. So simply, expecting an intact squall line of shwrs/tstms
associated in the vicinity of this strong sfc cold front that is
expected to move southeastward from its current position to very
roughly a Springfield(Robertson County)to Linden(Perry County)
line by 01/18Z, to then continue to push southeastward of the mid
state by 01/21Z, taking most of the convection potential with it.
Some discrete svr cells ahead of squall line possible, but most
activity is expected with the main squall line. Thus at least the
potential of a damaging wind event from 01/13Z(7 AM CST) -
01/21Z(3 PM CST) will be possible across our mid state region.
These extremely warm temps being experienced now/along with high
dewpoints and breezy conditions will continue until this strong
sfc cold frontal passage occurs, so highs today will be close to
temps the mid state is experiencing presently or just a few
degrees warmer, mainly in the low to mid 70s. Per these shwrs
and tstms expected, most locations across the mid state today
should at least experience some rainfall, with highest rainfall
amounts across the south and east, generally ranging from around
0.25 inch to around 1.25 inches. No organized flooding potential
is expected at this time, as any rainfall amounts received, in
general, will be below flash flood guidance values.

Taking a quick look at the rest of the forecast period, some
lingering light shwrs possible across the Cumberland Plateau
Region thru the mid evening hrs, otherwise clring skies and dry
conditions will prevail, as a CAA pattern becomes established as
sfc ridging influences from the Rockies build into the mid state
region. Temps will be close to seasonal values Thu and Fri. As
sfc high pressure influences shift eastward, temps will begin to
warm up again over the weekend with influences from another
frontal system expected during the first half of next week
bringing yet again chances of shwrs/tstms to region along with
seasonally warm temps with highs generally in the low to mid 60s
and lows in the lower 40s.

&&

.AVIATION...
12Z TAF DISCUSSION.

A band of strong to severe thunderstorms will move eastward near
60kt across Mid Tn this morning. Wind gusts in excess of 40kt are
expected with the storms at all sites, with locally severe gusts
over 60kt, and hail is likely. Isolated tornadoes are possible.
Main time for storms at CKV will be 12Z-14Z, for BNA 13Z-15Z, and
for CSV 15Z-18Z. Mainly MVFR conditions will be observed, but
brief IFR with the TSRA. Improvement to VFR will occur at all
sites by evening as winds become northwest with a frontal passage.

&&

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

&&

DISCUSSION......31
AVIATION........13

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Special Weather Statement
National Weather Service Nashville TN
527 AM CST WED MAR 1 2017

TNZ005-006-023>025-056-057-011215-
Hickman TN-Stewart TN-Dickson TN-Humphreys TN-Montgomery TN-
Houston TN-Perry TN-
527 AM CST WED MAR 1 2017

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN DICKSON...WESTERN
MONTGOMERY...STEWART...HOUSTON...NORTHERN PERRY...HUMPHREYS AND
CENTRAL HICKMAN COUNTIES UNTIL 615 AM CST...

At 524 AM CST, Doppler radar was tracking strong to severe
thunderstorms in west Tennessee, along a line extending from near
Sedalia to near Blue Goose. Movement was east at 65 mph.

Damaging winds are expected with these storms as they move into
Middle Tennessee beginning around 600 AM CST. Large hail will be
possible, and isolated tornadoes may occur. Warnings will likely be
issued as the storms approach.

Locations impacted include...
Dickson, Waverly, Centerville, Camden, Dover, Erin, Clarksville, New
Johnsonville, McEwen, Tennessee Ridge, Hurricane Mills, Big Rock,
Charlotte, Lobelville, Vanleer, Cumberland City, Slayden, Palmyra,
Bucksnort and Houston County Airport.

A tornado watch remains in effect until 1000 AM CST for Middle
Tennessee.

LAT...LON 3666 8785 3663 8785 3664 8735 3569 8738
      3569 8803 3573 8803 3577 8798 3592 8793
      3594 8793 3595 8801 3597 8802 3605 8799
      3613 8792 3617 8792 3622 8795 3631 8796
      3645 8806 3656 8803 3668 8807
TIME...MOT...LOC 1124Z 268DEG 59KT 3665 8866 3575 8864

13