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

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FXUS64 KMRX 212008

Area Forecast Discussion
National Weather Service Morristown TN
308 PM EST Sun Jan 21 2018

.SHORT TERM...(Tonight and Monday)...

Another mild day across the Southern Appalachians with temperatures
this afternoon in the upper 50s to mid 60s. Visible satellite
imagery indicates cloud cover lifting to th north and east as the
upper level ridge axis moves overhead. For tonight, models differ
greatly on fog formations. Winds just off the surface will be in 15-
25 kt range as cold front and upper level trough approach from the
west. Due to this, have only included a few small areas of patchy
fog in SW VA and NE TN. Overnight lows will continue to be above
normal with warm air advection ahead of the approaching system.
Lows will range from upper 30s to mid 40s.

On Monday, low level winds will increase as the pressure gradient
tightens with the cold front near the Mississippi River early in
the day. The winds at the 850 mb level will range from the 45-60
kt range and a wind advisory may be needed for the higher
elevations for late Monday into Monday night. For now, will
continue the mention of high winds in the HWO. The latest suite of
models is a bit slower with precipitation and have pushed back
PoPs until 18z for the Plateau. PoPs will progress to the east
throughout the afternoon. With the strong low level flow, PW
values will increase into the 0.9-1.1 inch range late in the day.
THese values are around the 90th-95th percentile for mid to late
January. The latest model guidance also indicates a narrow lounge
of instability moving into the area tomorrow afternoon and expect
there will be a few rumbles of thunder. At this time, not
expecting any strong or severe storms but if there is a stronger
updraft or two there would be the possibility for gusty winds at
the surface. Rainfall amounts by the end of the afternoon will be
light. The highest amounts will be across the Plateau and should
range from roughly 0.25-0.5 inches. Temperatures will continue to
be above normal on Monday with strong southerly flow. Highs will
range from upper 50 to mid 60s.

.LONG TERM...(Monday night through Saturday)...

Little change with the long term forecast. We start the period
with ongoing showers and perhaps a storm or two across our
southern areas. Cold front is located across middle TN and quickly
marching eastward. Winds will continue to be strong and gusty
overnight thanks to strong southerly flow and a tight pressure
gradient. The strongest winds will occur across the high terrain
but breezy conditions will also be in place for valley locations.
The front pushes east of our area a little before sunrise Tuesday
morning with colder air ushering in behind. Temps will stay quite
mild Monday night before the frontal passage. We could end up
having a midnight high on Tuesday as temperatures fall during the
afternoon due to strong cold air advection. Skies will briefly
clear immediately behind the front but wrap around moisture from
the low positioned to our north will bring in a second wave of
clouds and light precip through the day. Greater cloud cover and
chances for light precip are for the northern areas, mainly
northeast TN and southwest VA. Winds remain breezy on during the
day on Tuesday as the tight pressure gradient remains. Lingering
moisture tuesday night will transition over to light snow
showers,l little to no accumulation expected.

Northwesterly flow in place from Wednesday through Thursday but with
temps gradually warming. On Friday we see an area of high pressure
centered just off to our southeast which returns us to southwesterly
flow, further increasing temps. Highs on Friday will be back into
the lower to mid 50s. Southerly flow increases on Saturday as the
ridge amplifies in response to another trough moving in. Models have
been poor on timing of precip for Saturday. Best chances look to
occur Saturday night into Sunday but that may change due to poor
model agreement over the past few days. Highs on Saturday will be in
the mid to upper 50s with breezy conditions. The cold front moves
through on Sunday and temperatures once again drop.


Chattanooga Airport, TN             46  61  40  49 /   0  90  80  10
Knoxville McGhee Tyson Airport, TN  41  63  41  46 /   0  40  80  10
Oak Ridge, TN                       41  62  41  46 /   0  60  90  10
Tri Cities Airport, TN              37  62  40  46 /  10  20  80  30




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