Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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FXUS64 KMRX 182015

Area Forecast Discussion
National Weather Service Morristown TN
415 PM EDT Sun Mar 18 2018

.SHORT TERM...(Tonight and Monday)...
Shortwave ridging continues to dominate across the fcst area this
afternoon with partly cloudy skies highlighted along with weak nly
flow and slightly above normal temperatures.  The primary highlight
of the fcst period will be the possibility of severe weather
tomorrow afternoon/evening.  Not much change on that front as
moist/unstable air will sweep across the region into the morning as
a warm front surges northward.  Meanwhile, an upper low will track
through the OH valley providing ample lift for convection later in
the day.  Latest guidance favors a line of thunderstorms moving in
from the west late in the day Monday, with suffient moisture and
shear to support severe storms. With that, discrete supercells
looks like the favorable storm mode, at least early on before
merging into more of a linear feature perhaps with embedded
supercells. Thus, all severe threats will be possible, with the
best chances for tornadoes generally along/south of Interstate 40
where instability will be maximized. Further north tornadoes are
certainly not to be ruled out, however storms will be less
surfaced based thus presenting more of a wind/hail threat. SPC has
placed the majority of the region in the Slight risk, with a
subset of Enhanced risk areas generally across the southwest which
correlates well with the above mentioned enhanced tornado threat.
Although heavy rain is likely in association with some of the
stronger storms, storm motion looks to be sufficient to prevent
any widespread hydro issues.

.LONG TERM (Tuesday through Sunday)...An upper trough and low
pressure center will rotate into the Southern Appalachian Region on
Tuesday.  This will bring in cooler air and additional low level
moisture with weak lift.  The result will be widespread rain showers
moving through the area with the highest coverage expected over
northern locations.  The cooler air will continue to move in and by
Tuesday night...the ongoing rain will change over to snow across
higher elevations.  The upper low will rotate another lobe of
energy into the area on Wednesday...continuing the chance of
showers.  The upper low will be slowly pulling out of the area
allowing the scattered showers to end from south to north.  A few
showers may linger over northern areas and along the Appalachian and
with the cooler air in place Wednesday night...the rain will
transition to light snow or flurries during the night.  We should
briefly be between systems on Thursday for a dry period.  Model
consistency lessens through the rest of the extended and confidence
becomes rather poor. However...the overall trend is for the next
system of move in late Friday with a chance of showers Saturday
and Sunday.


Chattanooga Airport, TN             53  67  51  61 /  60  70  90  50
Knoxville McGhee Tyson Airport, TN  49  64  50  59 /  50  60  90  60
Oak Ridge, TN                       49  63  50  59 /  50  70  90  60
Tri Cities Airport, TN              43  60  46  54 /  20  50  90  60




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