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Area forecast discussion
National Weather Service Morristown Tennessee
316 am EST Sat Feb 24 2018

Short term...(today through sunday)...
latest water vapor and rap 500 mb analysis indicating weak
shortwave moving NE across middle and east Tennessee this morning as
strong ridge aloft remains anchored over the Bahamas. At the
surface, an area of light to moderate pcpn is moving NE across
middle Tennessee with most models indicating that northern plateau and SW
Virginia will see brief period of pcpn with this shortwave this
morning. Remainder of area could see a shower or possible
thunderstorm by this afternoon ahead of the approaching cold front
expected to finally push through the area on Sunday. Record high
temperatures should be safe today with increasing cloud cover
expected across the area. However any breaks in cloud cover, most
likely at cha/tys, could allow temperatures to Jump Up to near
records which sit at 79 for both sites, just set last February
24th.

Models are in very good agreement on developing low pressure over
the Great Plains today that will drive NE toward the Great Lakes
tonight and finally provide enough of a push in the low to middle
levels to finally move the frontal boundary across our area by
Sunday afternoon. Although there is some instability expected
along and in advance of this front, the early Sunday timing should
decrease any threat for strong to severe thunderstorms. However,
a 50 knots 850 mb jet ahead of the front Sunday morning, could mix
down some strong gusty winds in any showers or possible tstms that
may develop.

In addition to the wind threat, a marginal threat for localized
flooding also exists for this event mainly focused on our plateau
counties. Current mrms data is indicating about 1/3 inch of pcpn
associated with the shortwave this morning. Couple that with pws
that continue to be incredibly high for late February with values
of nearly 1.5 inches, which is typical of mid Summer and not late
winter. Areas tonight and Sunday could see up to an inch of rain
as the front moves through with some locally higher amounts to 1.5
inches possible before it ends Sunday evening. Although not a
widespread threat, rainfall amounts of over an inch in areas
already rain soaked this month could lead to some localized issues
and need to be monitored.

Long term...(sunday night through friday)...
the frontal boundary east of the Appalachians will move
slowly...allowing for moisture to continue across the region
Sunday night. Scattered showers will remain through the
night...with additional amounts of several tenths of an inch
possible in areas closest to the front in eastern Tennessee and SW
NC...while the rest of the area could see a couple of hundredths
of an inch additional accumulation.

Monday...drier air filters into the area as flow transitions to out
of the west-northwest. Rainfall will decrease from west to east through the
morning and early afternoon. Models try to keep rain over the entire
area through Monday night...though enough dry air and limited lift
will keep any showers from producing accumulating rainfall.

High pressure develops over the Ohio Valley and moves eastward
toward the Atlantic Tuesday. Clear skies and dry weather will be
present. Tuesday afternoon...low and mid level flow transition to
out of the SW as an upper level trough and low pressure system
develops over the Ohio Valley. Moisture funneled into the Tennessee Valley
will bring scattered to widespread showers beginning in the southern
plateau before sunrise Wednesday...and moving northeast to SW Virginia by
late morning. Precipitable water values will be above the 90th percentile...with
shower coverage and intensity expected to increase through the
afternoon as the low pressure system develops and upper level
divergence allows for plenty of lift.

The low pressure and strong mid level jet will move through the area
early Thursday morning through Thursday night. Winds will gust up to
30 mph across the area. Low level flow then slowly becomes more
unidirectional through the day from west to east...so would expect
storms to move quickly through the area. Instabilities are limited
around 1000 j/kg...so overall would expect strong winds and flooding
rains to be the main threat with this system.

By Thursday night...confidence decreases as models become widely
inconsistent. After the low pressure system moves NE Thursday
night...strong northwest flow will set up over the area. Moisture will be
limited...with showers decreasing from SW to NE Friday. Temperatures
are expected to reach much cooler temps...back into the 30s...for
low temperatures Friday night.



&&

Preliminary point temps/pops...
Chattanooga Airport, Tennessee 76 58 65 49 / 30 80 80 50
Knoxville McGhee Tyson Airport, Tennessee 75 58 65 48 / 40 70 90 50
Oak Ridge, Tennessee 74 58 66 48 / 50 80 80 30
Tri Cities Airport, Tennessee 73 56 68 46 / 60 60 80 50

&&

Mrx watches/warnings/advisories...
NC...none.
Tennessee...none.
Virginia...none.

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