FXUS64 KMRX 190811

Area Forecast Discussion
National Weather Service Morristown TN
411 AM EDT Mon Mar 19 2018

.SHORT TERM...(Today through Wednesday Night)...Very active
through the period. A series of short-waves and associated jets
will move through today and then again Tuesday and Wednesday.
Enhanced threat of severe weather today for Plateau, central and
southern Valley, and southwest North Carooina. The mid- week
upper trough and associated cold frontal passage will bring wintry
conditions back into the southern Appalachians with mountains
snowfall and widespread freeze for Wednesday night/Thursday

For Today, a short-wave and associated 120kt upper jet will move
into the lower Ohio and Tennessee Valley. The pressure falls with
the upper jet will strengthen the low-level jet pulling Gulf
moisture northward into the Tennessee Valley. Main question is how
far north will this push of moisture and instability go before
upper dynamic associated with upper jet pulls through this
afternoon and evening. Model soundings plenty of instability and
very strong shear to produce discrete supercells over middle
Tennessee and northern Alabama this afternoon, then race quicly
east northeast into the Plateau, southeast Tennessee and southwest
North Carolina. The greatest tornado threat will be across these
areas, but the Knoxville area could does have a threat of damaging
winds and marginal severe hail. Main timing of severe storms will
be between 5 and 7 pm ET Plateau to 8 and 10 pm ET central and
southern Valley, 9 and 11 pm ET southwest North Carolina.

The rest of the area can expect widespread showers and
thunderstorms with gusty winds and heavy rainfall.

Besides the convection, strong southerly winds will produce windy
conditions across the mountains and foothills late afternoon and

For Tonight, the storms exit the area this evening with dry slot
clearing sky. Clear sky, winds becoming light/calm, and wet ground
will allow widespread fog to develop. Some of the fog may be dense

For Tuesday and Wednesday, the upper low over Oklahoma and Kansas
will move across the Ohio and Tennessee Valleys. A cold frontal
passage Tuesday will produce widespread showers with enough
instability for thunder across east Tennessee, mainly TRI and TYS
areas. As the cold front moves through and approach of upper
trough, the vertical temperature profile will become cold enough
for the rain showers to change to snow showers over the higher
terrain. Snow accumulations of 2 to 4 inches are possible across
the far eastern Tennessee and southwest Virginia Mountains. Places
like the highest elevations of the Smoky Mountains and High Knob,
VA could see up to 6 inches throughout a 36 hour period. Main
concern is for any hikers getting caught off guard of the cold and
snowy conditions over the higher terrain.

Will highlight all of these concerns within our HWO and SPS
products, and DSS.

.Long Term (Thursday through Sunday)...The advertised dry period
still appears to be on track on Thursday with the offending deep
Eastern U.S. trough slipping out to sea, followed by an amplifying
upper ridge. The next low pressure system will be developing over
the Plains on Friday with eastward movement into the Midwest by 12z
Saturday. Typically, model solutions try to generate too much lift
over the Southern Appalachian region in the warm air advection ahead
of an approaching Middle America low pressure system. We see that
again in this mornings model runs for the period Friday through
Friday night; evidenced by a relatively high chance for showers
during the day Friday along with increasing probability Friday night
due to uncertainty in system timing. Tried to pull back on pops as
much as possible on Friday where the chance of rain this far in
advance of a developing mid latitude cyclone is rather low. The best
chance for showers; and even a thunderstorm or two would be Saturday
into Saturday night according to the latest modeling. Had to
broadbrush a chance pop for showers into Sunday due to uncertainty
in storm system timing. A welcome, but modest warming trend begins
on Thursday with continuation through Saturday. Sunday may not be
too unpleasant with weak cold air advection predicted behind the
weekend frontal system.


Chattanooga Airport, TN 67 52 62 36 / 80 100 60 40
Knoxville McGhee Tyson Airport, TN 67 51 60 35 / 80 100 70 70
Oak Ridge, TN 65 51 60 35 / 80 100 70 70
Tri Cities Airport, TN 65 48 63 37 / 40 100 80 90




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