Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 270849
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
349 AM CDT Sun May 27 2018

.DISCUSSION...

.Short Term(Today thru Tue Night)...

Mr Alberto will be the chief governing feature in this upcoming
weather forecast. He is currently moving north northeastward
at around 13 miles per hour across the eastern Gulf of Mexico.
Alberto is expected to move ashore early Monday morning and then
move across western/central portions of middle TN late Tues
afternoon and into Tuesday evening. More on this...later.

Current weather map this morning shows an upper level trough axis
over western TN while weak west to east ridging extends across the
Carolinas. This ridging feature will likely delay convective onset
for today. Will tier grids accordingly and include low pops for
morning...then becoming likely for most areas in the afternoon.
Convective temps slightly lower across southern areas, thus coverage
is likely to be better down there later today.

Tonight, it looks as though the deeper moisture and favorable UD
region will be south and southeast of our area. Convection will
occur primarily in the evening with the better coverage across our
southeast. Pops will be held down into the chance category.

Heights will be on the downswing by Monday afternoon as the n-s
trough sharpens in advance of Alberto. Divergence will be rather
pronounced in the afternoon according to the gfs. Euro solution
differs a bit and keep the deepest moisture further south and closer
to the center of Alberto. Will keep pops in the 40-50 percent range
as the Euro remains the model of choice given the tropical scenario.

On Monday night, Alberto will be marching up I-65. At that point it
is likely we will start to see some of the deeper moisture start to
arrive, especially toward sunrise. As mentioned before, Alberto will
move across western/middle TN on Tuesday. Low level wind energy will
pick up, especially east of the advancing center. SPC has posted a
marginal risk for severe weather on Tuesday across our eastern half.
This favorable right hand side of the storm track will need to be
watched as somewhat elevated helicity levels are indicated. Otw, the
biggest threat will be the potential of flooding. As of right now,
rainfall amounts through Wednesday will average 3 to 4 inches west
of I-65, and 1 1/2 to 3 inches east of I-65. The heaviest rainfall
is likely to occur during the day on Tuesday when 1 to 2 inches of
rainfall may occur in a rather short time span along and close to
Alberto`s track. By Tuesday night, models in agreement with lifting
the weakening Alberto northward and away from our area. ESF will
likely be issued a little later on and will stress the rainfall
threat in more detail.

As for wind speed potential, the hurricane center shows maximum
sustained winds of 25 kts when the center reaches northwest AL late
Tuesday afternoon. On Tuesday, the wind forecast for our area looks
something like east winds of generally 10-20 mph with perhaps some
gusts of 30 mph across southern areas. The elevated winds will
begin to decrease on Tuesday evening.

For our near term temperatures, with clouds expected to hold through
most of the period and rain increasing by Tuesday, look for max
temps to drop several degrees each day. For the upcoming wet
Tuesday, highs will top out in the upper 70s to lower 80s. These
numbers may fall further still as Alberto`s track becomes more
certain. Low temps will, as expected, be rather warm given the added
humidity. Upper 60s to near 70 can be expected, with mid 60s along
the Plateau.

.Long Term(Wed thru Sun Night)...

Leaned toward the latest ECMWF as it solution lines up better with
NHC current track for subtropical storm Alberto than latest GFS
solution. Both have Alberto as a tropical depression just north of
the mid state region shortly after sunrise on Wed. As Alberto pushes
further newd, sfc pattern will become more southerly gulf flow
orientated with time with no real sfc features on note until a sfc
front moves in from the central plains and drapes itself across the
mid state region by shortly after sunrise on Sun. Though certainly
not as much as Alberto will bring, this will continue the ushering
in of low level moisture across the mid state region for the
remainder of the work week into the upcoming weekend.

Expect an upper level trough to swing thru the mid state region
during the Wed morning hrs resulting in likely mdt shwrs and likely
tstms during the morning hrs, with a chance of mdt shwrs and a
chance of tstms during the afternoon hrs. Look for another upper
level trough to at least approach the mid state region as Wed night
progresses, with a chance of light shwrs and a chance and tstms.
As this broadening upper level trough with embedded disturbances
pushes thru the mid state region during the day on Thu, anticipating
likely light shwrs and likely tstms. Thu night thru Sun night will
be characterized by upper level ridging influences building across
the srn plains newd into the Great Lakes region thru the weekend.
However, both the ECMWF/GFS solutions keep the mid state just east
of the eastern periphery of these ridging influences, meaning that
moisture will still be plentiful enough with building north nwly
flow to support a slight chance to chance of light shwrs and a
slight chance to chance of tstms Thu night thru Sun night. Sky
conditions will be cloudy to mocldy during the first half of the
forecast period becoming ptcldy as the weekend progresses.

Total areal average QPF values Wed morning thru Sun night will range
from around three inches across locations approaching the TN River
Valley to around one and only half inches across the Cumberland
Plateau Region. With this additional rainfall after the passage of
Alberto in mind, and in coordination with the short term portion of
the forecast dealing with the main brunt of rainfall impacts of
Alberto, will be issuing a hydrological outlook (ESF) product later
during these early morning hrs to highlight total amounts of
rainfall expected thru next seven day period along with associated
flooding chances.

As for temps, a warm air advection pattern should become increasingly
established across the mid state region as the second half of the
work week into the upcoming weekend progresses as a sfc sly flow
pattern becomes increasingly pronounced. Afternoon high temps on
average will be 4-5 degrees above seasonal normal values on Wed
afternoon, low to mid 80s, around 80 Cumberland Plateau Region.
Afternoon high temps by the weekend will be generally in the upper
80s, mid 80s Cumberland Plateau Region. Overnight lows during this
time period will generally be around 10 degrees above seasonal
normal values, around 70 degrees, upper 60s Cumberland Plateau
Region.

&&

.AVIATION...
06Z TAF DISCUSSION.

Obs trends indicate conditions are becoming conducive for MVFR
fog development within the next few hours. Calm to light and
variable winds with dewpoint depressions less than 5 degrees are
noted, with CSV already seeing VIS drop to 8SM. Will need to
monitor for possible IFR VIS at BNA and MQY where decent rainfall
was observed earlier in the day. Afternoon convection is expected
to return after 18Z tomorrow.


&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      88  69  86  69  80 /  40  30  40  20  70
Clarksville    88  69  83  69  82 /  20  20  30  20  70
Crossville     81  66  80  65  78 /  50  50  40  30  60
Columbia       86  67  85  68  79 /  50  40  30  30  70
Lawrenceburg   85  67  84  68  79 /  50  50  30  30  70
Waverly        86  69  83  69  80 /  30  20  50  20  70

&&

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

&&

$$

DISCUSSION......21
AVIATION........31



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