Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 201941

Area Forecast Discussion
National Weather Service Nashville TN
241 PM CDT Fri Oct 20 2017


Models are still adjusting to the upcoming weather system moving
in on Sunday and continuing through Tuesday. For the most part,
models have slowed down a bit which will put most of the rainfall
early Monday morning through Monday evening. The NAM is the
outlier being much faster than the consensus, so didn`t deviate
too much from previous forecasts just yet. More on that below.

For the first half of the weekend, southerly winds will be on the
increase, so temps will continue to slowly warm up Saturday and
Sunday. Before that, temps will drop tonight into the mid 40s to
low 50s, but it looks like southerly winds will be just strong
enough to prevent falling much cooler than that. In areas where
winds do calm down overnight, temps may be a bit cooler. Also have
mention of fog over bodies of water and low lying areas for
Saturday morning as well. Winds will pick up mid morning across
the area, and some cloud cover will sneak into the mid state as
well. With the stronger southerly winds, mixing may compensate for
the lack of sunny skies, so still expecting highs in the 70s to
around 80.

On Sunday, the upper ridge will slide off the east coast and the
large Plains trough will continue eastward towards our area. The
GFS and ECMWF line up pretty well, but still slightly off.
Consensus between all models has precip moving across the TN River
Sunday morning/afternoon, with slight chances along the I-65
corridor Sunday afternoon. Areas east look to stay dry with
current solutions until Sunday evening/overnight into Monday
morning. The reason for the slow down of the upper trough looks to
be a result of the upper jet strengthening on the backside of the
wave, and forcing the trough to dig south and close off aloft before
moving further east. The closed upper low separates from the main
trough, and accelerates eastward. The broad trough looks to regain
strength and dig southward midweek to reinforce cold air advection
across the region.

Before the additional cold air moves in, rainfall amounts from the
first trough and associated cold front currently looks to be
between 1 and 3 inches, with the higher amounts near the TN River
Valley. PWAT values between models looks to be above 1.5 inches
late Sunday afternoon through Tuesday afternoon, and soundings
look completely saturated on Monday. With the best forcing over
the area on Monday as well, it looks like most of the rain will
fall on Monday as mentioned earlier. Temps aloft have warmed up a
bit as well, so just have slight chance mention of thunder for now
with moderate to heavy rain showers during the day Monday. Tuesday
looks to have some backside precip chances, but mainly east of
I-65, but then the main cold front moves through which pushes
precip chances off to the east.

Wednesday morning will bring the first below 0C 850 mb temps to
the mid state this fall. Tuesday afternoon winds behind the front
will be between 10-20 mph during the afternoon bringing in that
cold air. Overnight lows are in the upper 30s to low 40s Wednesday
morning, but any clearing or lighter winds compared to the
forecast could easily drop temperatures further. Lows are in the
mid 30s Thursday morning, so may be seeing some frost and or a
light freeze possibly on the Plateau Wednesday or Thursday

Ridging tries to move in Thursday and Friday, so warmer temps move
back into the area, but only highs in the 60s. The GFS and ECMWF
are surprisingly in good agreement in the extended, and if the
solutions pan out, we could be in store for another cold blast
next weekend with another strong trough bringing precip chances on



VFR flight rules for most of this TAF cycle. Will still be dealing
with IFR/MVFR fog Saturday morning as temperatures fall back into
the upper 40s, but only for a couple of hours prior to daybreak.

Winds will be light to calm with mainly a southeasterly fetch.


Nashville      50  80  59  81  64 /   0   0   0  20  70
Clarksville    49  78  60  78  60 /   0   0  10  40  70
Crossville     46  73  52  73  59 /   0   0   0  10  40
Columbia       48  79  58  79  62 /   0   0   0  20  80
Lawrenceburg   48  78  58  78  62 /   0   0   0  30  80
Waverly        50  78  60  78  62 /   0   0  10  40  80





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