Severe Thunderstorm Warning 25, NWS Morristown, TN

Area Forecast Discussion
National Weather Service Morristown TN
313 PM EDT Mon Mar 19 2018

.SHORT TERM (Tonight and Tuesday)...Scattered convection is moving
into the area this afternoon with the main band of strong
thunderstorms expected to form over middle TN/northern AL and will
then move into the MRX CWA this evening. The air mass continues to
destabilize with CAPE values climbing above 1000 J/kg in some
southern locations. A strong upper jet is moving in with a 40+KTs
850MB jet pushing in creating good low level shear. All of this
has created an unstable air mass that will support strong to
severe thunderstorms as they move in. The main threat from this
evening storms is damaging winds...though large hail is also
expected. Additionally...tornadoes will also be possible mainly
over southern areas. This significant line of convection should
exit the area by midnight with just a few lingering showers
possible overnight. Also of concern is the 850MB jet may create
strong...gusty winds over higher elevations of the Appalachians. A
Wind Advisory will be issued for the higher elevations of the Smokys
and surrounding areas. With the recent rainfall and some
clearing...could see areas of fog form by sunrise. On
Tuesday...the upper low will swing into the region bringing cooler
air and enough low level moisture and weak lift for scattered to
widespread showers. However...by this time...the atmosphere should
be stable and do not anticipate any thunderstorm activity.

.LONG TERM (Tuesday night through Monday)...We start the period with
an area of low pressure swinging across the forecast area with
ongoing light rain showers in place. As the low pulls east Tuesday
night, colder air will advect into the region with stout nw flow
behind the low. As temperatures drop through the night, rain will
transition over to snow. The highest elevations will see snow as
early as 00Z Wednesday. The snow line will quickly work its way down
in elevation and areas around 3000/4000 feet should be seeing snow
by roughly 03z. Depending on which model you look at, snow could
start as early as 09Z for some valley locations and by 12z at the
latest. Depending on how quickly the rain transitions over to snow
in valley locations will determine the amount of accumulation, if
any. As of now it looks like our favored upslope terrain, above 5000
feet, could see 2 to 4 inches with up to 6 across areas such as
Mount LeConte, Sam's Gap, and Roan Mountain. Areas between 2000 and
4000 feet 1 to 3 inches. Portions of the northern plateau, northeast
TN, and southwest VA up to an inch in some valley locations. Where a
dusting is possible across the central valley. We will continue to
watch this system closely, especially as soon as we get past our
severe weather event moving through tonight. A mountain zone winter
weather advisory is likely with the next forecast update tomorrow
morning. Light snow showers still in place Wednesday morning but
tapering off by late morning for the valley. Light snow showers will
linger on and off across the high terrain through the day. Highs on
Wednesday are the coldest of the period with highs in the upper 30s
to mid 40s. A few light snow showers could even linger into
Wednesday night due to the upslope flow. Lows overnight will be in
the mid to upper 20s for most.

Ridging tries to start building in for Thursday and Friday but we
are on the eastern side so northwest flow will continue. This won't
allow temps to rebound too quickly but warmer than Wendesday. Highs
on Thursday and Friday in the low to mid 50s. The rest of the
extended looks wet as our next system approaches. Highs will be in
the lower 60s with chance and likely POPS in place.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             52  61  36  49 / 100  50  30  10
Knoxville McGhee Tyson Airport, TN  51  58  35  41 /  90  70  70  50
Oak Ridge, TN                       50  57  34  43 /  90  80  70  40
Tri Cities Airport, TN              48  57  35  40 /  90  90  80  70

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...None.
TN...Wind Advisory from 8 PM this evening to 3 AM EDT Tuesday for
     Blount Smoky Mountains-Cocke Smoky Mountains-Sevier Smoky
     Mountains-Southeast Monroe.

VA...None.
&&

MJB/SR

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