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

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FXUS64 KMRX 280922

National Weather Service Morristown TN
422 AM EST Fri Feb 28 2020

.SHORT TERM (Today and Tonight)...Two shorter wavelength features
will move across the Southern Appalachian region within the
circulation of the amplified eastern U.S. long wave trough during
the period. The first wave is evident in satellite and radar
imagery dropping steadily southeast through the Ohio Valley into
the Mid South early this morning. Some light radar returns
occurring over the Ohio River at 09z with light precipitation
edging into Western Kentucky and Western Tennessee. Soundings for
this event reveal that temperatures will be just cold enough for
some light snow accumulations at elevations of around 2500 ft and
higher on the northern counties of the Cumberland Plateau, in the
higher terrain across Southwest Virginia and over the mountains on
the Tennessee and North Carolina border.

The main axis of deeper moisture and lift will be centered over
the forecast area later this morning into the early afternoon
hours so the main period of precipitation will only be around 3-4
hours; with exception in some of the higher terrain across
Southwest Virginia and over the far East Tennessee mountains where
a westerly upslope component could keep a few snow showers going
later in the afternoon. These higher terrain areas could pick up
anywhere from around an inch to as much as 2-4 inches with this
first short wave. Much of the Great Valley will just see a
mixture of snow and rain with little snow accumulation due to the
expected later arrival of the light precipitation around mid day
when surface temperatures have warmed at least a few degrees above
freezing. The main area where some light snow may accumulate for
a period in amounts ranging from a dusting to possibly one inch on
grass covered surfaces will be across the valleys of Northeast
Tennessee and Southwest Virginia where surface temperatures will
be a little closer to the freezing mark through late morning
before slowly rising into the mid 30s.

The second short wave builds in later this evening through the
pre-dawn hours Saturday. This feature will have the benefit of
colder surface temperatures due to the loss of insolation and
therefore, accumulations in the valley in Central East and
Northeast Tennessee through the valleys of Southwest Virginia
could see a dusting to possibly one inch by daybreak Saturday. Of
course the higher terrain areas in the Winter Weather Advisory
could see additional snowfall accumulations of one to as much as
3 inches in the higher elevations above 3500 ft.

So, the atmosphere will be just a little too warm to keep rain
from mixing with the snow today in the lower elevations with highs
expected to reach the upper 30s and lower 40s north with even
middle and upper 40s south. The higher terrain will be a different
story where temperatures will rise only to the upper 20s to around
30 degrees. Lows tonight will drop to the middle and upper 20s
north to the lower and middle 30s south.

.LONG TERM (Saturday through Thursday)...Saturday morning snow
showers mainly in VA and our mountains will end quickly thanks to
dry advection. Great day Sunday with highs 55- 60 in the Valley.

Sunday sees a H5 low pressure trough moving into northern CA, which
will then dig into the desert SW by Monday night. This will draw a
moist west-southwesterly tap that will bring rain back to our region
beginning Monday. Models notoriously struggle with the strength and
ejection of these systems, and the 00Z GFS is presently faster than
the 00Z ECMWF and Canadian. These differences will be reflected in
the ultimate timing and placement of the heaviest accumulating rains
from Monday through Thursday next week, as well as just how warm-
sectored we may or may not be. Note that it is possible that event-
total precip next week could exceed three inches in portions of the
forecast area. But we have several days to monitor the evolution of
the models` handling of the event.



Flight condition will remain vfr for several more hours as an
upper level disturbance builds closer to the Great Valley. Around
14-19z a combination of ceilings and visibility will reduce flight
operations to mvfr with some periods of ifr in heavier showers.
Should be a rain and snow mix as the precipitation builds in with
precipitation ending around 19-21z along with an improvement to
mvfr or even vfr ceilings late in the period.


Chattanooga Airport, TN             47  32  48  31  60 /  70  30   0   0   0
Knoxville McGhee Tyson Airport, TN  42  29  43  28  58 /  70  40  10   0   0
Oak Ridge, TN                       43  29  44  28  58 /  80  60  10   0   0
Tri Cities Airport, TN              39  26  38  23  55 /  70  70  20   0   0


TN...Winter Weather Advisory from 7 AM this morning to 7 AM EST
     Saturday for Blount Smoky Mountains-Campbell-Claiborne-
     Cocke Smoky Mountains-Hancock-Johnson-Morgan-Scott-Sevier
     Smoky Mountains-Southeast Carter-Southeast Greene-Southeast

VA...Winter Weather Advisory from 7 AM this morning to 7 AM EST
     Saturday for Lee-Russell-Wise.


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