Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 201158
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
558 AM CST Fri Jan 20 2017

.UPDATE...
FOR 12Z AVIATION DISCUSSION.

&&

.SHORT TERM...
(Today thru Sunday)...

Sfc low pulling north across IN this morning. The rainfall has now
moved out of the area with the western extent of the precipitation
now across eastern TN. Patchy fog persists in a few spots and will
therefore include it in the early portion of the today period. Otw,
low cloudiness and some patchy light shower activity will be
possible today. Will include generally 20 pops.

Tonight will represent a break before the next storm system. There
might even be a few breaks in the cloudiness in the evening. Then,
rainfall chances will return on Saturday as some upper level energy
works northeastward across our area. Rainfall amounts will range
from just a tenth across our north to one half inch south.

Moving on, models continue to show a rather strong and persistent
closed upper level low, which will move across the deep south Sunday
and Monday. This feature will generate some additional dynamical
cooling, perhaps a few degrees cooler than what the models indicate.
However, the system looks to be on the warm side with 850 mb temps
of +2C to +4C beneath the core. Thus, I will undercut temps a few
degrees but it looks like a rain event. In fact, tstms will need to
be included as lapse rates ramp up along with an increase in
lower and mid level cape values.

For our area, will include categorical pops for Sunday and Sunday
night. Rainfall amounts will average around 1 inch as the
deformation zone looks to be setting up over us.

Temperatures through Sunday will remain on the mild side. Lows will
be 50 to 55, highs 60 to 65. Will need to watch those temps on Sat
nt and Sun. They may need to be lowered a bit.

.LONG TERM...
(Mon thru Thu)

A transition back to at least temps around seasonal normal values is
expected from the second half of the work week into the first part
of next weekend. So, Ole man winter still has something up his
sleeve for the mid state this winter season. Before then, however,
mild conditions that have been the norm as of late will continue.
The highlights of this fluctuating wx transitional episode will be
marked by some lingering light shwrs possible on Mon, with upper
level ridging influences building in Mon night and Tue, providing
dry conditions along with a WAA scenario. A weak frontal system will
push thru the mid state region Tue night into Wed bringing with it
iso to sct light shwrs. A CAA scenario should build in behind this
frontal passage though, with some lingering moisture Wed night, but
temps at this time look to remain just above freezing enough to
ensure that any pcpn that falls will be in liquid form. There should
be enough lingering moisture reinforced by moisture associated with
an upper level trough that will begin swinging in from the Ohio
River Valley Region to support iso light shwrs on Thu and possibly a
winter mix Thu night into Fri. Taking a closer look at temps, high
temps on Mon will be mainly in the low 50s, lows Mon night in the
upper 30s, warming to highs in the mid to upper 50s on Tue, lows in
the mid 40s Tue night, and even into the upper 50s to around 60 on
Wed. That CAA scenario working into the mid state region will result
in lows Wed night back into the mid to upper 30s, with high/low
temps falling to around seasonal normal values by the first part of
next weekend.

&&

.AVIATION...
12Z TAF DISCUSSION.

Models hanging onto below VFR ceiling thresholds thru 21/12Z BNA
but punching thru the VFR ceiling threshold at least for a portion
of the forecast period CKV/CSV. However, believe the VFR
thresholds will punched thru at BNA also as drier works in from
the south, with sustained sfc winds 5 to 10 kts expected thru
21/12Z, before yet another slug of low level moisture works into
the mid state region 21/06Z-21/12Z. Some VFR fog with some passing
light shwrs in vcnty of terminals thru 20/15Z expected also.
Predominate MVFR ceilings should become VFR around 5 kft
20/18Z-20/20Z. As above mentioned slug of low level moisture
from the south works into region after 21/06Z, ceilings should
return to MVFR thresholds with MVFR/IFR vsbys possible CSV
approaching 21/12Z.

&&

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

&&

$$

DISCUSSION......21
AVIATION........31



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