Special Weather Statement, NWS Morristown, TN

AREA FORECAST DISCUSSION
National Weather Service Morristown TN
255 PM EDT Tue Aug 10 2021

.SHORT TERM (Today through Tomorrow)...

Key Message:

1. Scattered showers and thunderstorms today, a few of which should
be strong/severe with damaging winds, cloud to ground lightning, and
brief heavy rainfall being the primary hazards.

Discussion:

Currently scattered showers and thunderstorms across the Ohio and
Tennessee Valleys this afternoon. Generally zonal flow in the mid
levels and weak surface ridging is present as some ripples of energy
traverse through the mid level flow. CAMs have still had a hard time
getting a handle with convective initiation and how long storms will
last under this weather regime. But now that there is convection
currently ongoing, expect for it to continue through the rest of the
afternoon and into the evening. These storms will have a good amount
of instability to tap into, with deeper instability compared to
yesterday. Model soundings and mesoanalysis indicate generally 2500+
J/Kg of MLCAPE across the area, with the highest amounts being
further west across Plateau, Middle TN, and central KY. Still not a
lot of shear at all through the atmosphere with generally less than
10 knots of 0-6km present, but there's maybe just a bit more
directional shear than what we saw yesterday. So expect storms to
not be long lived, but should have a more favorable environment for
sustained strength compared to yesterday afternoon. Also of note is
increased DCAPE values across the entire region (generally above 800
J/kg) with the drier air in the mid levels and a more inverted V
sounding... So downbursts or strong straight-line winds is most
likely the main threat with storms today. Based on current radar
trends expect the best chances for storms is still along the higher
terrain along the mountains and plateau...But as the afternoon
progresses the outflow from these initial storms should help spark
off additional convection into the evening hours. Based on soundings
and mesoanalysis still think that most storms today should remain
pretty uneventful, but expect to see additional strong to severe
storms as the afternoon progresses. Greatest threat for these
stronger storms is generally north of I-40 and near the Cumberland
Plateau.

Several CAMs still try and bring in the remnants of an MCS out of
northern KY overnight into tomorrow, but certainty on this is low as
the timing has been all over the place with this system. Looks like
it should be pretty benign if it makes it into northeast TN or
southwest VA, but will maintain low end PoP chances overnight to
account for any shower/storm that's able to make it this far south.
Another round of fog can also be expected overnight with the valleys
and areas that receive moderate rain the most likely to see the
densest fog.

As we move into tomorrow we could see another round of showers and
thunderstorms develop in the late morning or early afternoon. But
once again there isn't really a strong synoptic forcing mechanism
for storms over our area, with better chances likely east of the
mountains. But overall the atmospheric profile should be somewhat
similar to this afternoon so with diurnal heating of the surface we
should see more convection in the typical areas along the mountains
and plateau.

ABM

.LONG TERM...(Wednesday Night through Tuesday)...

Key Messages:

1. Warm temperatures are expected mid to late week with highs in the
lower 90s in the Tennessee Valley.

2. Scattered showers and thunderstorms are expected every
afternoon/evening. Better coverage is expected Friday, Saturday and
Sunday as a front moves into the region.

Discussion:

-Wednesday Night through Friday-

The long term period of the forecast begins Wednesday evening with
broad upper level troughing over central Canada and the northern
Plains States. This trough will continue to progress eastwards into
the Great Lakes region by the end of the work week as an upper level
ridge across the eastern portions of CONUS begin to weaken. PWAT
values will be hovering around the 1.8-2.0in value through the
majority of the extended period. Paired with peak heating, afternoon
showers and thunderstorms can be expected Thursday as the boundary
layer destabilizes. Some lingering activity is possible overnight,
with the better chance occurring in southwest VA and the northern
portion of the Plateau.

By Friday, shortwave pulses moving through the upper level flow will
deepen the base of the trough over the Great Lakes. At the surface,
high pressure over the northern plains will begin to shift eastward
and low pressure over Illinois will begin to dive into the Ohio
Valley along with an associated frontal boundary. Showers and
thunderstorms on Friday afternoon/evening will likely see an
increase in coverage relative to previous days with additional
forcing available as the front approaches the region from the
north/northwest.

-Saturday through Tuesday-

The better coverage of showers and thunderstorms will likely
continue throughout the weekend as the frontal boundary appears to
stall out over the region. With low level moisture remaining
abundant, some isolated flooding may be possible with stronger
storms, especially any areas that see repeated showers or storms
over this upcoming relatively wetter period. The better coverage of
precipitation over the weekend along with lowering H5 heights will
also act to lower high temperatures back to seasonal normals into
the start of the work week.

KS

&&

.AVIATION...
18Z TAF DISCUSSION.

Another afternoon of showers and thunderstorms is expected across
the area. In the TAFs have highlighted the time frame of the
greatest coverage of storms with a TEMPO group. It's still
possible to see a storm outside of the TEMPO hours, but chances
should be much lower once the sun begins to set. Expect some more
fog in the morning with KTYS/KTRI having the highest chance of
fog. Not a lot of certainty on how dense the fog may end up being,
but will wait to see where rain occurs which should give a better
understanding for fog potential.

ABM

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             74  92  74  92  73 /  30  30  20  40  20
Knoxville McGhee Tyson Airport, TN  74  92  73  93  73 /  20  40  10  40  20
Oak Ridge, TN                       72  91  72  92  72 /  20  30  10  30  20
Tri Cities Airport, TN              70  89  69  91  69 /  30  50  20  40  30

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&

Hazardous Weather Outlook
National Weather Service Morristown TN
258 PM EDT Tue Aug 10 2021

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-111900-
Cherokee-Clay-Scott-Campbell-Claiborne-Hancock-Hawkins-Sullivan-
Johnson-Morgan-Anderson-Union-Grainger-Hamblen-Northwest Cocke-
Cocke Smoky Mountains-Northwest Greene-Southeast Greene-
Washington-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-Russell-
258 PM EDT Tue Aug 10 2021 /158 PM CDT Tue Aug 10 2021/

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

.DAY ONE...This Afternoon and Tonight

Scattered showers and thunderstorms will continue through the
afternoon and into the evening. Some of these storms could be
strong to possibly severe with damaging winds, cloud to ground
lightning, and brief heavy rainfall being the primary threats.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not needed at this time.

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