Area Forecast Discussion
Issued by NWS Nashville, TN
FXUS64 KOHX 051749
Area Forecast Discussion
National Weather Service Nashville TN
1149 AM CST Mon Dec 5 2016
FOR 18Z AVIATION DISCUSSION.
Precip moved out of the area earlier yesterday evening and left
the mid state with cloud cover head of the next shortwave trough.
temperatures should be on the rise for the remainder of the day as
WAA precedes the troughs arrival Tuesday morning. Models seem to
agree that most of the precip will fall during the evening tonight
and overnight into Tuesday morning, with slight chances for
thunderstorms still lingering in the forecast. Models have backed
off on instability a bit, but the shear remains around 50-60 knots
from 0-6km, and with a dynamic upper shortwave, still cant rule
out some thunderstorms this evening and overnight.
Rain chances will continue Tuesday morning, with even some slight
chances for thunder still in northeast zones. As the upper
shortwave moves towards the northeast, rain chances will come to
an end from west to east during the day. By Tuesday evening, a
brief dry period will move into the region ahead of a larger
trough moving in from the Great Plains for the late
For early Thursday, the GFS and ECMWF have lined up nicely in
regards to upper flow patterns, however they still do not agree on
precip timing and amounts. The GFS has gone much drier than
previous solutions, and the drying trend has now taken out all
mention of precip over the mid state. The ECMWF has also trended
drier, but still places precip over the area Thursday morning. The
biggest change for this event was the ECMWF, which went from a
decent wet solution to nearly dry, so it seems models are trending
drier for Thursday morning. Backed off pops a bit to reflect this,
and if the drying trend continues, we may be just left with a
strong dry cold front to cool off temps later in the week. For
now, have chance pops during the Thursday morning timeframe. Also,
temperatures are cool enough that some snow will mix in, so did
not make any changes to having snow mentioned with the rain where
Thursday night through Saturday still look very cold, with lows
Thursday night behind the cold front hitting the teens for most of
the mid state. Highs on Friday will see about half of the mid
state not getting above freezing, while others just barely get
into the mid 30s. Lows in the 20s Friday night will give way to
some 40s on Saturday thanks to some early WAA ahead of the next
shortwave trough to impact the region.
Both the GFS and ECMWF have changed their solutions for the system
coming in next Sunday. Both have weakened the shortwave a bit, and
significantly warmed the low levels. Still have some snow mention
late Saturday night into Sunday morning, however after that both
models have much warmer air moving in and look to have rain for
the mid state for the duration of the event. WAA will keep temps
above freezing Sunday night and highs will get to the mid 50s on
Monday. Both models also line up well with precip, and have likely
pops Sunday night and into the day Monday. After Monday, however,
the GFS and ECMWF begin to diverge starting with the strength and
amplitude of the next two troughs from next Tuesday through
Thursday, so it will be interesting to see how the next few runs
resolve the model differences.
18Z TAF DISCUSSION.
Upper low over TX this afternoon. Low level southern jet spreading
ample moisture northward. Associated sfc low to track northeast
from the northwestern gulf to the middle TN area by 12z Tues.
Shortwave axis will traverse the area between 12z and 18z. Hence,
we are looking at a wet taf period. Rainfall should begin between
21z and 00z this afternoon and evening. Heaviest rainfall appears
that it will occur between 06z and 12z. At that time, upper
divergence will be at its peak.
As the sfc low reaches the upper Plateau, instability levels will
climb. There may be an isol thunderstorm or two. However, given
that this is the latter quarter of the taf pd, will refrain from
the inclusion of any tstm activity so as to keep the latter
portions of the taf from being to informative. Instead, will
include a continuation of light shower activity along with the
apparent wind shift.