Area Forecast Discussion
Issued by NWS Nashville, TN

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397
FXUS64 KOHX 180851
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
251 AM CST Mon Dec 18 2017

.DISCUSSION...

A crummy day is on tap across the mid-state as we continue to deal
with the backside of yesterday`s weather system.  Copious low
clouds, poor visibilities and drizzle are plaguing Middle Tennessee
at forecast time and this is likely to continue into a good portion
of the morning daylight hours. We`re monitoring the necessity of a
Dense Fog Advisory for the morning commute hours. It looks like the
worst of it is south of the I-40 corridor, closer to the Alabama
state line. We are currently covering these poor conditions area
wide with an SPS, and with only one or two sites showing 1/2 mile,
an advisory may not be necessary. Conditions are likely to
improve as we move into the afternoon hours and while a few peeks
of sun are possible, mostly cloudy skies are likely to keep
temperatures at bay this afternoon, so I`ve had to come down a
couple more degrees for afternoon highs.

We then turn our attention to the first of two soakers this week.
This first system will originate out of Texas on Tuesday.  As the
warm front associated with this system pulls northward, it will
bring with increasing rain chances.  Light rains could start for
Middle Tennessee as early as Tuesday morning, however the bulk of
the heavy rainfall is more likely to move into the area Tuesday
night and Wednesday.  Rainfall totals on the order of 1 to 1.5
inches are possible, especially for those south of I-40.  This is
where the heaviest of the rains are likely.  While there isn`t much
in the way of surface based instability, forecast soundings are
suggesting quite a bit of dry air aloft Tuesday afternoon, so there
will be a chance of elevated thunderstorms closer to the Alabama
state line during the afternoon and then again in the evening when
the upper low passes over the region.  No severe weather is
expected, but it could get breezy on Wednesday with the passage of
the surface low.

We should dry out Wednesday night and Thursday and in fact, warm
into the 60s on Thursday as skies clear out and boundary layer winds
shift around to the south.  However, the dry conditions will be
short lived as the second system of the week begins to move into the
TN Valley late Thursday night and Friday.  This system continues to
be portrayed as being very dynamic.  While no severe weather is
expected, forecast soundings are suggesting extremely high PW values
Friday and Friday night -- easily 2 SD above normal.  Coupled with a
40+ kt LLJ and a system that slows and gets elongated with time,
rainfall totals could be very high with this system.  Both the GFS
and Euro solutions are in agreement about 2+ inch storm total
rainfall, which means some spots will see more than that.  This is
still Day 5, however, if these forecast storm totals are persistent,
some flooding will be possible.

Models diverge greatly after Friday.  The GFS is dry and the Euro
wants to quickly bring the Friday`s cold front back northward,
bringing even more rain into Middle TN Sunday and Monday. This would
be a worst case scenario as rainfall totals from Friday to Monday
could be in excess of 4+ inches.  However, with the drastically
different solutions, I`ll just carry a chance PoP for Sunday and
Monday.  The Euro does suggest the possibility of some wintry mixed
precip towards the end of the forecast, but not for the Christmas
timeframe, so it looks like anything that falls for Christmas
will be of the liquid variety.

&&

.AVIATION...
06Z TAF DISCUSSION.

Expect VIS to bounce around IFR and LIFR at times for most sites
with CIGS likely to remain IFR, except at CSV where LIFR
conditions are anticipated through the night. After daybreak
VIS and CIGS will slowly improve with MVFR CIGS for much of the
day.

&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      56  45  60  48  54 /  10  10  40  80  70
Clarksville    54  43  59  44  50 /  10  10  30  80  70
Crossville     53  42  59  46  55 /  10   0  50  90  90
Columbia       56  45  60  49  54 /  10  10  60  90  80
Lawrenceburg   57  45  60  50  55 /  10  10  60  90  80
Waverly        54  46  58  48  51 /  10  10  40  80  70

&&

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

&&

$$

DISCUSSION......Unger
AVIATION........04



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