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

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FXUS64 KMRX 240738

Area Forecast Discussion
National Weather Service Morristown TN
338 AM EDT Tue Oct 24 2017

.SHORT TERM...(Today and Tonight)...Time to break out the winter
coats and hats as a reinforcing shot of cold air moves into our area
via a secondary cold front. This front is associated with a closed
upper low and strong vortmax divign down into the existing longwave
trough and will help to amplify it even greater. There will be
minimal moisture with this front so only slight chance POPs for
showers up across NETN and SWVA for the first half of the day. After
that, will have in slight chance POPs across the eastern mountains
for the afternoon and overnight hours. Any precip that occurs will
be very light, only expecting trace amounts up to a hundredth of an
inch or two.

Greater cloud coverage across northern areas compared to the
southern valley for today. Winds will be gusty this afternoon due to
the tight pressure gradient, winds will gust up to 25mph at times.
Temps will only reach into the lower 60s, which is around 5 to 8
degrees below normal. Temps fall into the mid to upper 30s for most
areas tonight. Clouds and light winds should keep temps above
freezing but it is possible a few isolated locations, especially
across the high terrain, could reach freezing. Due to winds and
clouds am skeptical that any frost develops but isolated patchy
frost possible in sheltered valley locations that see calmer winds.
Lows will 5 to 8 degrees below normal. With the falling temps late
tonight the highest peaks across the eastern mountains may see a
flurry or two if enough moisture can be squeezed out.

.LONG TERM...(Wednesday through Monday)...The longwave trough axis
will be to the east of the Appalachians to start the long-term
forecast. Northwesterly flow aloft and in the low levels will
continue to advect in colder air into the region. Wednesday will
see highs only topping out in the 50s across the valley and 40s in
the mountains. Late Wednesday night into early Thursday morning a
shortwave trough will rotate around the western periphery of the
departing longwave trough. This shortwave will five across the
Western Great Lakes into the OHio River Valley and Central
Appalachians. PW values will be in the 0.4-0.6 inch range around
the 10th-25th percentile for late October. However, models do
indicate enough lift for a few sprinkles mixed with some light
snow across southwest Virginia and the higher elevations along the
Tennessee and North Carolina line. Due to the limited moisture,
not expecting any impacts. The main impact Wednesday night into
Thursday morning will be the widespread frost with light winds and
temperatures dropping down into the 30s. Based on current
guidance, a freeze will be possible as well across portions of
southwest Virginia and northeast Tennessee.

A shortwave ridge will move across the area on Thursday.
Temperatures will moderate some with higher heights across the
region. Forecast highs for Thursday are in the upper 50s to upper

The pattern will become amplified on Friday as a trough dives
southeast out of the Northern Plains into the Mid-Mississippi River
Valley as a second shortwave to the south dives across the Mountain
West into the Southern Plains. Even though it is still several days
away, the GFS and ECMWF are both in fairly good agreement with the
overall pattern and timing for the weekend. At the surface, a cold
front will race across the Plains into the Mid and Lower Mississippi
River Valley on Friday. Southwesterly flow will develop across the
Gulf Coast into the Ohio River Valley with moisture advecting in
ahead of the approaching system. The cold front will move across the
area on Saturday with widespread showers along the boundary. Models
are not forecasting much in the way on instability and have not
included any thunderstorms at this time. Post-frontal precipitation
will continue Saturday night into Sunday as a strong jet develops
across the Southern U.S. The 120-140 kt jet will put the forecast
area in the left exit region with continued synoptic support for
lift and precipitation. With this lift persisting behind the front
and cold air advecting in, the question becomes will there be any
wintry precipitation. For now, have included a mix of rain and snow
in the forecast for northeast Tennessee and southwest Virginia
Sunday night into Monday. This is still several days away and do not
expect any impacts.


Chattanooga Airport, TN             63  40  57  38 /  10   0   0   0
Knoxville McGhee Tyson Airport, TN  62  39  54  37 /  10  10   0   0
Oak Ridge, TN                       62  39  53  37 /  10  10   0   0
Tri Cities Airport, TN              62  36  51  34 /  10   0  10  20




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