Severe Thunderstorm Warning 7, NWS Morristown, TN

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1220 PM EST Tue Jan 3 2023

...New AVIATION...

.UPDATE...
Issued at 1021 AM EST Tue Jan 3 2023

The forecast looks on track in regard to the timing of
showers/storms in our area this afternoon, and the potential for
severe storms. Comparing radar to the latest CAMS, convection is
slightly ahead of where the CAMS depict, with the FV3 being the
closest. Convection is expected to arrive in our Plateau counties
around 1-2 pm, with the window of strong to severe storms expected
between 2 and 6 pm. During this time frame, surface-based CAPE in
the southern TN Valley/Plateau reaches to 500-1000 J/kg. In a
high shear environment, that amount of instability may be adequte
to support a severe threat. Linear convection will produce mainly
a straight-line wind gust threat, although embedded
notches/discrete cells may produce a tornado threat as well for
the southern counties. Floding will be a lesser threat, but
training cells will need to be watched for persistent heavy rain
over the same locations.

Wind gusts in the mountains have been in the range of 30-45 mph in
most mountain/foothills obs, so the Wind Advisory will continue.

Some adjustments will be made to temperatures for the morning
update, as some locations in the lee of the mountains are warmer
than forecast, likely due to downslope winds and some breaks in
the clouds.

&&

.SHORT TERM...
(Today through Wednesday)
Issued at 235 AM EST Tue Jan 3 2023

Key Messages:

1. Two rounds of showers and thunderstorms, possibly severe, are
expected this afternoon and again early Wednesday morning.

2. Moderate to heavy rainfall will lead to at least some isolated
threat of flash flooding.

3. Strong winds expected in the mountains of east Tennessee today.

Discussion:

In general, an upper low over the KS/NE border early this
morning, will lift into the upper midwest over the next 24 hours.
The associated surface low will lift from Iowa into MN/WI during
that same time, with a cold front moving from the Ozarks early
this morning eastward into our forecast area by roughly daybreak
Wed.

As mentioned above, there will be two rounds of convection to
focus on in terms of impacts/severe chances. The first will come
this afternoon as a shortwave rotates around the upper low and an
associated 300mb jet streak shifts northeast from AL/MS into the
TN valley. Ongoing convection early this morning from western KY
down into northern MS, will be shoved towards eastern TN through
the day as this occurs. The second round will come around or just
before daybreak Wed morning as the cold front with this system
moves into the region.

As far as severe chances go, there is still some uncertainty for
both time periods. SPC HREF probabilities for surface based CAPE
of 500 J/kg or greater is mostly in the 30-40 percent range this
afternoon and mainly south of I-40, and almost non-existent during
the early morning hours tomorrow ahead of the front. Conversely,
deep layer shear is on the lower end of supporting damaging winds
this afternoon as the initial wave of convection moves in but is
far more significant along/ahead of the front tomorrow morning.
However the presence of rich Gulf moisture (with dewpoints in
excess of 60 degrees), effective inflow layer wind shear and
helicity values that are supportive of damaging winds and even a
tornado threat (50-70kt and upwards of 200 m2/s2 respectively),
and even modest instability will yield a severe threat for both
this afternoon and ahead of the cold front tomorrow morning. This
afternoon I would expect the threat to be damaging winds and
somewhere in the vicinity of the I-40 corridor where the incoming
line of storms overlaps relatively better instability. And for
early Wed morning it seems mainly the southern areas will be the
places of concern for damaging winds and possibly a tornado threat
as well.

With regards to flooding concerns, that will be isolated in nature.
PWATs are going to be quite high for this time of year and though
each round of convection will move west to east, individual
storms within each round will be moving SSW to NNE, which will
provide an opportunity for at least some training of storms.
This could produce some localized flash flooding. However the
expected storm total rainfall amounts in the 1-2" range isn't a
QPF signal that points to a lot of flash flooding threat.

Lastly, increasing low level wind fields this morning should be
enough to produce some advisory level wind gusts in the mountains.
The H85 wind directions will be more southwesterly which doesn't
translate into a strong mountain wave event typically. Thus will
keep the advisory as is and stick with the gusts to 55 mph
wording. Windy spots like Cove Mtn will likely gust higher but in
large part, believe the advisory will suffice.

By Wed afternoon the cold front should be pushing east of the
Appalachians, with drier conditions and cooler/drier air pushing
in from the west. Have rain chances lingering well into the
afternoon hours, but it should be winding down quickly after
1-3pm.

&&

.LONG TERM...
(Wednesday night through Monday)
Issued at 235 AM EST Tue Jan 3 2023

Key Messages:

1. Dry and near normal temperatures for Wednesday night through
Friday.

2. Chances of rain return to the forecast over the weekend, with
near normal temperatures continuing.

Discussion:

Wednesday night through Friday...

The closed upper low across the Great Lakes will slowly lift north
with surface high pressure settling across the southern plains.
With moisture moving out of the area, expect clearing skies and more
tranquil weather conditions. This trend will continue Thursday and
Friday under high pressure. Temperatures will finally return to near
normal levels Wednesday night through Friday.

This weekend, upper flow becomes quasi-zonal as a strong jet moves
across the plains and into the Tennessee Valley. An area of low
pressure will likely develop lee of the Rockies, associated with
this jet and slowly lift across the plains and Ohio valley. Moisture
return ahead of this system is a bit uncertain, but lower-
tropospheric moistening resulting from increased synoptic ascent
should be sufficient for slight chance to chance PoPs. Can't rule
out some wintry p-types in the higher terrain areas, but still a
ways out to pinpoint with any degree of certainty. Temperatures over
the weekend will remain near to just above normal.

&&

.AVIATION...
(18Z TAFS)
Issued at 1215 PM EST Tue Jan 3 2023

A line of showers and thunderstorms is approaching the TAF sites
from the west. It is expected to bring TS and MVFR vis/cigs at CHA
between 20-22Z, and at TYS between 21-23Z, with IFR conditions at
times. Gusty winds and a shift to the west will also accompany
the line. Some weakening is expected before the line reaches TRI,
where TS is less likely and conditions should stay on the MVFR/VFR
margins. A second round of storms is possible late
tonight/tomorrow morning, and the TAFs will have MVFR conditions
and TS with that round, although confidence about the details is
low at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             62  69  42  57 / 100  50   0   0
Knoxville McGhee Tyson Airport, TN  60  68  41  54 / 100  80   0   0
Oak Ridge, TN                       59  68  39  54 / 100  80   0   0
Tri Cities Airport, TN              56  66  41  53 /  80  90  10   0

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Wind Advisory until 4 PM EST this afternoon for Blount Smoky
     Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky
     Mountains-Southeast Carter-Southeast Greene-Southeast
     Monroe-Unicoi.

VA...NONE.
&&

SHORT TERM...DGS
LONG TERM....Diegan
AVIATION...DGS

Hazardous Weather Outlook
National Weather Service Morristown TN
812 AM EST Tue Jan 3 2023

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-041315-
Cherokee-Clay-Scott TN-Campbell-Claiborne-Hancock-Hawkins-
Sullivan-Johnson-Morgan-Anderson-Union-Grainger-Hamblen-
Northwest Cocke-Cocke Smoky Mountains-Northwest Greene-
Southeast Greene-Washington TN-Unicoi-Northwest Carter-
Southeast Carter-Roane-Loudon-Knox-Jefferson-Northwest Blount-
Blount Smoky Mountains-North Sevier-Sevier Smoky Mountains-
Sequatchie-Bledsoe-Rhea-Meigs-McMinn-Northwest Monroe-
Southeast Monroe-Marion-Hamilton-Bradley-West Polk-East Polk-Lee-
Wise-Scott VA-Russell-Washington VA-
812 AM EST Tue Jan 3 2023 /712 AM CST Tue Jan 3 2023/

This Hazardous Weather Outlook is for portions of southwest North
Carolina...east Tennessee and southwest Virginia.

.DAY ONE...Today and Tonight

A strong storm system will affect the area today and Wednesday.
Strong to severe thunderstorms are possible this afternoon, and
again on Wednesday morning. This potential for severe storms is
expected to be mainly in southeast Tennessee and the Cumberland
Plateau. Damaging wind gusts are the main threat, with a low
potential for an isolated tornado. High winds with gusts above 50
mph are likely in and near the mountains today. Also, locally
heavy rainfall and isolated flooding will be possible, mainly
south of Interstate 40.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

No hazardous weather is expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and on Wednesday
morning.

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