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

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FXUS64 KMRX 142026

National Weather Service Morristown TN
326 PM EST Sat Dec 14 2019

.SHORT TERM (Tonight and Tomorrow)...

A shortwave trough is currently rotating through the region behind
the main upper level wave. Radar imagery indicates light scattered
showers generally across the northern 2/3rd`s of the forecast area.
Temperature in the higher elevations above roughly 4-4.5 kft are at
or below freezing. The latest NewFound Gap observations is at 31
degrees. For these higher locations, expect light snow will still be
possible throughout the afternoon with some minor accumulations of
less than an half inch possible. Visible satellite imagery indicates
some clearing across the southern valley and plateau with water
vapor imagery indicating drier air there. Based on latest trends,
looks like there could be some clearing further north before clouds
build back in later tonight. With sunshine, temperatures have warmed
quickly at Chattanooga into the mid-50s and will adjust high
temperatures this afternoon to account for this.

Precipitation chances will decrease throughout the late afternoon
and evening hours as the upper level trough progresses to the east.
PW values this evening into the overnight hours will drop down into
the 0.3-0.4 inch range. Model soundings indicate some low to mid-
level moisture as another quick moving trough moves through the
region overnight. Do not expect there will be any precipitation with
this but will see another increase in cloud cover. The low level
moisture will become trapped below a subsidence inversion on Sunday.
The GFS is very aggressive with mixing things out shortly after
sunrise giving way to mostly sunny skies. The NAM holds onto this
low-level moisture through noon or so. Therefore, held onto clouds a
bit longer than the previous forecast. Surface high pressure will
become established across the western Atlantic on Sunday with
southerly flow in the low level over the Gulf Coast. A warm front
will lift northwards across the Southeastern U.S. during this time
but should stay to the south of the forecast area throughout the
short-term forecast period. Lows tonight will range from the mid to
upper 30s for most locations with highs on Sunday in the upper 40s
to mid 50s.


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

Sunday night will end the brief dry period with west to east flow as
trough develops over the northern plains and rockies and low
pressure also forms over the southern plains with moisture moving
into the western Mississippi and Ohio Valleys Sunday night. A warm
front will form and move north of the region by Monday. Only light
rainfall amounts expected overnight. A strengthening southwest flow
aloft will keep temperatures in the 40s to lower 50s overnight with
rising temperatures western sections late in the night. Monday
temperatures will rise even more into the lower to mid 60s. A weak
surface low will move from AR east northeast across MS and into TN
and KY. Increased shear and some instability will allow for
thunderstorms to develop just ahead of the front Monday night into
Tuesday morning. A few strong storms are possible over the plateau
and southeast Tennessee with that area in a marginal risk in the day
3 outlook. Rainfall amounts will be quite heavy as well across the
plateau and southeast Tennessee and southwest North Carolina late
Monday and Monday night. Amounts could exceed 2 inches with
localized flooding possible. Tuesday the high temperatures will come
early as strong cold front will be through the area early in the
morning. Expect steady to falling temperatures and some snow showers
to develop by afternoon over the higher elevations. Tuesday evening
models moving moisture out a little sooner with only a few hours of
precipitation falling after sunset. Only minor snowfall
accumulations expected in the mountains...less than 1 inch. Higher
pressure with colder temperatures and clear skies Wednesday and
Thursday. Friday models want to develop a closed low over Saturday
er the central Mississippi Valley and this could bring in some
precipitation Friday night and Saturday. It could be cold enough for
a rain/snow mix depending on time of day and elevation. Only have
slight chance pops for now.




Ceilings currently range from MVFR/VFR across the terminals with
scattered light precipitation. Added VCSH to the TAF at TYS/TRI
through 21z based on the latest radar trends. TRI is currently
MVFR and expect these ceilings will continue through the TAF
cycle. Ceilings are currently VFR at TYS/TRI around 4-5 kft and
model forecast soundings support a return to MVFR later tonight.



Chattanooga Airport, TN             39  57  48  66  47 /  10  10  30  50  90
Knoxville McGhee Tyson Airport, TN  38  53  46  65  48 /  10   0  20  50  90
Oak Ridge, TN                       38  52  46  64  46 /  10  10  30  50 100
Tri Cities Airport, TN              36  49  39  63  48 /  20  10  10  40 100



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