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

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FXUS64 KMRX 210113

National Weather Service Morristown TN
913 PM EDT Tue Oct 20 2020




Forecast for the remainder of the night generally looks to be on
track. Still expecting some fog to develop, but how extensive and
dense is still uncertain. Other than beefing up the fog a bit, mainly
just some minor tweaks to temps and dew points with this update.



The only concern for aviation weather is possible formation of low
clouds/fog late tonight into early Wednesday. MVFR level clouds
are expected to develop at CHA which may hinder fog, but fog looks
more likely at TYS/TRI. How much vsby restriction can be expected
is still uncertain, but for now will take conditions at TYS as
low as IFR and TRI to LIFR for a short period around sunrise.
Otherwise, VFR conditions are expected for the period all sites
with light winds.


/ISSUED 313 PM EDT Tue Oct 20 2020/
SHORT TERM...(Tonight through Wednesday)...

Not a whole lot to talk about during the short term. High pressure
anchored to our east will allow for a mostly quiet period. Biggest
forecast challenge will be fog development tonight. Mostly going
with a persistence forecast for tonight since conditions haven`t
really changed. Tonight, mostly clear skies will give way to some
early morning clouds along with some patchy dense fog. Fog should
mainly be confined to locations near or along area waterways.
Overnight lows will be mild with temps in the low to mid 50s, which
is around 5 to 10 degrees above normal.

Tomorrow, clouds and fog will mix out during the mid to late morning
hours with plenty of sun by late morning/early afternoon. Highs
tomorrow will be around 8 to 10 degrees above normal with temps in
the upper 70s to near 80.


LONG TERM...(Wednesday night through Tuesday)...

Main theme for the extended will be continued unseasonably warm

For Wednesday night through Thursday night, surface and upper
ridging will keep conditions dry and unseasonably warm. Another
round of patchy fog near area waterways is expected Wednesday
night/Thursday morning.

For Friday and Saturday, ridging breaks down across the southern
Appalachians allowing a weakening frontal boundary and very limited
upper dynamics move into the region late Friday. Scattered to broken
showers are expected as we move into mainly Friday night and
Saturday.  Latest GFS shows some marginal instability for thunder
and will include for Saturday afternoon.

For Sunday through Tuesday, strong jet dynamics dives into the Great
Basin and southwest United States. This allows for increasing
heights/ridging over the southern Appalachians. A series of jet
dynamics lifts up of this deepening upper trough. One such was move
out across the mid-section of the nation Sunday tightening the
pressure gradient over the Tennessee valley.

For Monday and Tuesday, the tightening pressure gradient will
strengthen the boundary layer southerly jet pulling unseasonably
warm conditions into the area. Strong jet dynamics/upper trough will
remain west of the area keeping the brunt of the convection west
of the area.



Chattanooga Airport, TN             56  81  60  81  62 /   0   0   0   0  10
Knoxville McGhee Tyson Airport, TN  53  79  56  80  59 /   0   0   0   0  10
Oak Ridge, TN                       53  80  56  80  59 /   0   0   0   0  10
Tri Cities Airport, TN              50  78  52  78  55 /   0   0   0   0   0



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