Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 250820
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
320 AM CDT Mon Sep 25 2017

.SHORT TERM...
(Today thru Wed)

Simply put, not much of an overall wx pattern change expected
thru Wed afternoon with ridging influences sfc/aloft continuing
to be the wx player across the mid state region. Especially
early this morning, periods of sct/bkn ci can not be ruled out
also, as an area of bkn CI continues to move slowly north
northwestward along and west of I-65 corridor as of 25/08Z.
The continuance of this overall wx pattern would continue to
support patchy fog development overnight and possibly into the mid
morning hrs during the tonight and Tue night time frames. Patchy
fog formation may not be as thick in isolated locations as being
experienced early this morning tonight and Tue night due to less
low level moisture pooling potential. But looking at this morning
approaching 25/08Z, at least a couple of obs site were
experiencing vsbys at 1/4 of a mile or less. Will continue to
monitor the situation as these early morning hrs progress. Will
make final decision near press time if the issuance of an SPS is
needed to highlight the development of isolated dense fog,
especially near bodies of water and other usual mid state fog
prone locations at least across the eastern half of mid state
where skies are presently moclr. Calm winds and favorable dewpoint
depressions are already in place across the entire mid state, and
continued timing progression movement north northwestward of the
area of bkn ci will play a key in determining fog potential and
associated visibility restrictions across wrn portions of the mid
state.

A progression from nely sfc flow to nly flow is expected as the
first half of the work week progresses due to enhanced subsidence
across our region as Hurricane Maria approaches the Carolina
coastline. Can not totally rule out a microscale/localized
shwrs/tstm developing during diurnal max heating influences, but
more than likely, this enhanced subsidence will bring an end to
the iso afternoon shwrs/tstm activity of the last few days, i.e.
the mid state will be dry thru the first half of the work week.
Skies will generally be moclr expect from late morning thru early
evening hrs per diurnal heating influences which will result in
the development of sct CU fields.

As for temps, may make some minor tweaks as press time approaches,
but with not much of an overall wx pattern change means afternoon
high temps will continue to be seasonably warm, and in some
locations approach 10 to 12 degrees above seasonal normal values
thru Wed afternoon. Consensus of 850mb temp profiles show little
if any temp fluctuations thru Wed afternoon also. Afternoon high
temps will generally be in the upper 80s, mid 80s Cumberland
Plateau Region. Lows tonight and Tue night will be in the mid
60s, lower 60s Cumberland Plateau Region.

31

.LONG TERM...
(Wed night thru Sun)

Wednesday night and Thursday, a cold front will be positioned to the
south of the mid state. This new airmass will carry a rather shallow
push of cool air. In fact, upper ridging will still extend from the
northwestern Gulf northeastward across the deep and mid south. Mrh
values do elevated late Wed nt and into Thu. However, forcing is ill-
founded in the post frontal sector and will therefore keep
conditions dry.

On Friday, the upper ridge will undergo suppression. This will allow
another moisture starved cold front to push through. The associated
sfc high will be moving southward from central Canada and will bring
us some cooler weather. By Sunday, the sfc high will shift across
the mid Atlantic states and our winds will become light
southeasterly. A small degree of moisture return is expected but not
enough to warrant the inclusion of pops.

For the ext temps, at this point it still looks rather warm for Wed
nt and Thu. As was previously mentioned, the airmass will possess a
rather shallow layer of cool air. We will still see highs in the mid
80s west of the Plateau for Thursday. However, after the Friday
fropa, the intrusion of cooler, more seasonal, air is looking
likely. 850 mb temps will drop down to between 10c and 12c and this
will equate to high temps in the mid to upper 70s. Compared to
seasonal norms, overnight lows will not be too low because of a lack
of close proximity in regard to the prevailing sfc high. Look for
mins to dip down into the 50 to 55 degree range for Friday morning
and through the weekend.

21

&&

.AVIATION...
06Z TAF DISCUSSION.

Mostly VFR conditions for this TAF cycle, however there will be
some MVFR/IFR fog at all terminals after 06Z. IFR more likely just
before sunrise.

Winds will be light to calm through the cycle.

&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      91  67  91  66  91 /   0  10   0   0   0
Clarksville    89  64  89  64  89 /   0  10   0   0  10
Crossville     85  61  85  61  85 /   0   0   0   0   0
Columbia       88  65  88  64  88 /   0  10   0   0   0
Lawrenceburg   87  65  87  64  87 /   0  10   0   0  10
Waverly        87  66  87  66  87 /  10  10   0   0  10

&&

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

&&

$$

DISCUSSION......31
AVIATION........Unger


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