Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Nashville Tennessee
745 PM CDT Wednesday Mar 12 2014
allowed the Wind Advisory to expire as the pressure gradient
continues to weaken and the strong surface low in the NE continues to
quickly exit NE and being the New England area their severe weather.
Still seeing some light precipitation developing associated with some 500
mb vorticity maxes over the eastern two thirds of the area. Due to the
very low freezing level and 8-10 degree c dewpoint depressions below
the freezing level...a mixture of snow pellets/sleet/rain have
been reported throughout much of the middle state. This should turn
to all snow...albeit light with no accumulation. This energy
looks like it will continue through 03z for west of the Cumberland
Plateau and through 06z on the plateau. Thus extended the slight
chance probability of precipitation out to the west to better capture the current radar
trends and model 500 mb vorticity energy. Also bumped probability of precipitation on the plateau
up to 30 percent.
Previous discussion... /issued 627 PM CDT Wednesday Mar 12 2014/
00z taf discussion.
Scattered cold air advection -shra/-shsn continue to spread across the northeast half
of middle Tennessee near all three airports with csv reporting -sn
recently. Some -shsn will continue off and on at csv through the
evening...but not expecting much at bna/ckv and will only mention
vcsh. VFR ceilings at bna/ckv and MVFR ceilings at csv will continue
tonight before exiting Thursday morning. Current gusty northwest
winds will gradually subside through the night...then begin to
veer to a more westerly direction by the end of the taf period.
Previous discussion... /issued 326 PM CDT Wednesday Mar 12 2014/
winds still blowing in the 20 to 30 miles per hour range. Gradient is expected
to weaken through 00z but will go ahead and allow the advisory to
continue until then. Otw...cold front has now worked itself south of
the middle state. Current temperatures are generally in the lower 40s.
Shortwave axis to work east of the area tonight. However...there is
some backside energy that could produce a few rain/snow showers
across the plateau tonight and a few late afternoon showers west
of plateau. Will therefore include 20 probability of precipitation for the plateau and
include late afternoon wording to cover the isolated shower
activity west of the plateau. Otw...cold temperatures for the overnight.
Lows will generally be in the 20s.
Another cool day is expected on Thursday. 850 mb temperatures do rebound
nicely by 00z however. Additionally...low and middle level subsidence
is rather pronounced and this should aid with the apparent upcoming
parcel mixing. Therefore...I will go slightly above the mav
guidance. Not as cold Thursday night as the SW 850 mb flow begins to
elevate by 12z.
On Friday...surface gradient will tighten up as a frontal system
strengthens over the plains. For now...looks like winds in the 15 to
25 miles per hour range.
In our extended forecast...aforementioned frontal system will weaken as
it approaches and will become a non-player as the bulk of the surface
forcing shifts well north of the area. A large reason for this is
because of a lack of upper level support. The pattern is more zonal
and lacks the infusion of any shortwave activity. This will chance
as we move into Saturday. Shortwave development over the western
U.S. Will translate into the development of a strong surface low over
Texas. This low will morph into a rather strong inverted trough as will
move eastward with the axis cross the middle state on Sunday morning.
Rain looks likely for the Saturday through Sunday period with around
an inch of rainfall expected. There will also be a slight chance of
thunderstorms for Sat nt as showalter values approach zero. Severe