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

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FXUS64 KMRX 062025

Area Forecast Discussion
National Weather Service Morristown TN
325 PM EST Tue Dec 6 2016

.SHORT TERM (Tonight and Wednesday)...
A dry westerly zonal flow will persist through the short term.
Lingering light rain this evening will move out of the area...
and a dry day is expected for Wednesday. High temperatures will be
near normal...but cold air will rush into the area and result in
very cold weather beginning Thursday.

.LONG TERM (Wednesday Night through Tuesday)...
Polar front jet shortwave moves N of the area Thursday. At the same
time, a ribbon of subtropical energy rides NE out of Mexico and
across the SE US. At the surface, weak reflection of this energy
aloft will briefly raise POPs to chance as this feature moves
rapidly through the area. Without much moisture to work with, and
very little cold air in place by then, expect any pcpn to be mainly
liquid...although a very brief mix is possible in our NW counties at
the onset of the event Thursday morning if moisture is available.
Also could see a brief period of northwest wind snows over higher
terrain of NE TN after the system moves through...but squeezing out
any moisture by that point will be very difficult. Expecting no
accumulations. Once this feature moves through by Thursday evening,
temperatures will fall with the coldest air of the season upon us
Friday and Friday Night.

Next event begins Sunday with some disagreement between GFS and
ECMWF on timing and location of this event. Differences lie in the
middle level flow with past few runs of GFS digging a fairly strong
trough over the middle US Sunday morning while ECMWF runs have had a
nearly zonal flow across much of the eastern 2/3 of CONUS. By Monday
morning, GFS is already lifting the trough NE toward New England
while ECMWF starts/continues digging this trough eastward toward the
Middle Atlantic coast by Tuesday morning. Resultant timing of pcpn
with this system is a little slower and much moister in ECMWF while
GFS is rather quick across the area, ending pcpn by Monday
afternoon. Although there will be a small window for frozen pcpn
Sunday morning, best pcpn chances do not really start until lowest
layers have warmed Sunday afternoon. Once again, some areas in
higher terrain may see a dusting of snow in the post frontal winds,
however accumulations are not likely.

At the very end of the period on Tuesday, GFS again develops a
system along the southern stream of the jet. Unfortunately had to go
with blend of models as none them appear to be taking the lead in
the handling of this event.


Chattanooga Airport, TN             40  54  37  46 /  10   0  30  30
Knoxville McGhee Tyson Airport, TN  39  51  35  44 /  10   0  30  30
Oak Ridge, TN                       39  52  35  44 /  10   0  30  20
Tri Cities Airport, TN              36  51  35  42 /  30   0  20  30





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