Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 250909
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
409 AM CDT Wed Apr 25 2018

.SHORT TERM(Today thru Fri Night)...

Sfc obs at 25/09Z(4 AM CDT) showing best patchy fog potential,
some dense, west of TN River Valley Region, despite the
persistence of low cloud coverage and sfc winds speed in many
locations around 5 mph. However, in a few locations, patchy fog
has developed across the mid state in locations where lighter to
calm winds are prevailing. Will mention the possiblity of patchy
fog developing in these most favorable locations, low lying
locations and locations near bodies of water, thru the mid
morning hrs today.

Otherwise, an unsettled wx pattern looks to continue thru at least
the afternoon hrs on Fri. Quandaries concerning specific
location(s) wx are still there over the short term forecast
period. So, let`s explore what should happen in a general "big
picture" scenario and look closer at any specifics that might be
able to bring some clarity too.

A weak sfc front will approach from the cntrl MS River Valley
Region later this morning and eventually push thru the mid state
region this afternoon. Subtle upper level ridging influences
developing as the morning hrs progress will give way to a more
zonal flow pattern aloft with the possibility of an embedded
shortwave within by the late afternoon hrs today, a as closed
upper level low moves into nrn portions of the southern plains by
this evening. Will mention iso light shwrs across Cumberland
Plateau Region this morning, with iso light shwrs across entire
mid state region this afternoon.

Have leaned toward the latest GFS/NAM solutions which look most
reasonable and are recommended also by WPC`s latest Model
Diagnostic Discussion. A closed upper level low is expected to
remain well defined, almost like a "bowling ball" in upper level
flow aloft, as it initially moves sewd out of the nrn srn plains,
then ewd just south of the he mid state region, before moving newd
into the Carolinas as Thu night progresses. Consensus of latest
GFS/NAM solutions showing that despite its track south of mid
state, upper level troughing influences will come into play thru
out the entire 24 hrs on Thu across our area. Atm instability
supportive of even iso tstm development should remain close to
track of upper level low center and thus remain south of the mid
state region. However, as early as this evening, for locations
generally west of I-24, increasing chances of light shwrs are
expected the closer one gets to the TN River Valley Region, with
the possibility of iso light shwrs spreading ewd across all most
all of mid state region, expect for the higher elevations of the
Upper Cumberland, after midnight tonight.

Because of upper level troughing influences moving across the mid
state region though during the entire day on Thu, with associated
embedded disturbances aloft rotating around base of these upper
level troughing influences, now it looks like most of the mid
state, expect locations near the TN/KY border, will be
experiencing numerous light shwrs on Thu morning. Numerous shwrs
producing mdt rainfall will be possible during the afternoon hrs
for locations generally along and south of I-40 and across the
Upper Cumberland Region as increased moisture, instability, and
more pronounced upper level disturbances provide needed lift.
Also it looks like a weak sfc low will develop across nrn MS by
sunrise on Thu morning and push newd into srn portions of the
Cumberland PLateau Region by Thu afternoon, aiding in mdt
rainfall development also. There could be some lingering iso to
sct light shwrs across locations east of I-65 Thu evening as upper
level low pressure center shifts newd, and possibly some iso
light shwrs lingering across the Cumberland Plateau Region after
midnight Thu.

Fast moving sfc cold front will move in from the cntrl plains on
Thu evening and push rapidly across the mid state during the day
on Fri. Upper level troughing, and possibly another upper level
closed low, will once again develop across nrn portions of the
southern plains Thu evening, but the greatest pronouncement of
these upper level troughing influences moving sewd and well south
of the mid state region. However, this track will result in
synoptic upper level troughing influences spreading newd and
across the mid state region by Fri afternoon. Iso light shwrs will
continue to be possible across Cumberland Plateau Region during
Fri morning hrs, with iso light shwrs possible across the entire
mid state on Fri afternoon.

Finally, sfc ridging influences out of the srn Rockies will build
into the mid state region, along with a dry nwly flow pattern
aloft. This will result in an ending to the unsettled wx pattern
that the mid state has been experiencing as of late. Dry
conditions along with decreasing cloudiness is expected as Fri
night progresses.

In most locations, saturated ground conditions continue to
persist across the mid state region. Even with the potential
of some mdt rainfall being experienced across southern and
eastern portions of the mid state region on Thu afternoon,
as of this time, no organized flooding threat is expected.
As of this time too, total additional rainfall amounts from today
thru Fri afternoon look to generally be less than an inch
across southern portions and the Cumberland Plateau Region and
less than a half inch elsewhere across the mid state.

As for temps, as for afternoon highs, they will remain seasonable
cool thru Fri afternoon per associated variable to cloudy skies.
Afternoon highs today will be around 70 TN River Valley Region
to lower 60s Cumberland Plateau Region. Sfc frontal passage today
will usher in some cold air advection behind it, thus highs on
Thu afternoon will be even cooler, with highs generally in the
lower 60s, around 60 Cumberland Plateau Region. However, with a
more sly sfc flow pattern developing as the day progresses on Fri,
afternoon highs will get closer to seasonal normal values.
Afternoon highs on Fri will mainly be in the upper 60s to around
70, mid 60s Cumberland Plateau Region. As for overnight lows,
overnight lows tonight, though, will be seasonably mild, mainly
in the lower 50s, around 50 Cumberland Plateau Region. Per above
mentioned cold air advection pattern, lows Thu and Fri nights will
be in the mid 40s.

31

.LONG TERM(Sat thru Tue)...

A beautiful spring weekend is ahead. The center of a large high
pressure system will move from the Upper Midwest to the Mid Atlantic
Region through the weekend as an upper level ridge forms. This
pattern will bring clear and seasonably cool nights with lows in the
40s. Days will be sunny and mild with highs mostly from the upper
60s to mid 70s.

Return flow around the surface high will help warm temperatures well
into the 70s on Monday and Tuesday, with some areas topping 80. A
few showers may develop in our western counties Tuesday afternoon,
but for the most part, it looks like the upper level ridge will keep
us free of any significant rain chance through most of next week.

13

&&

.AVIATION...
06Z TAF DISCUSSION.

Showers have diminished around airports this evening with just
some sprinkles or drizzle expected overnight. Current VFR cigs at
CKV and MVFR cigs at BNA/MQY will become MVFR/IFR overnight before
improving to MVFR on Wednesday morning and VFR by afternoon. IFR
cigs at CSV will become LIFR overnight before rising to MVFR on
Wednesday morning. Light north to northwest winds are expected
through the TAF period.


&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      68  53  65  47  70 /  20  20  70  10  20
Clarksville    70  51  65  45  69 /  20  20  40  10  20
Crossville     63  49  60  45  64 /  20  20  70  50  20
Columbia       68  55  63  46  69 /  20  40  70  10  20
Lawrenceburg   67  53  62  46  68 /  20  20  70  20  20
Waverly        70  52  64  45  70 /  20  40  60  10  20

&&

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

&&

$$

DISCUSSION......31
AVIATION........Shamburger



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