Not expecting anything really bad. By the time the storms get here, there will be very limited instability. There may be an isolated severe threat over the plateau, but the storms will be weakening as they approach East TN.
I was in west Knoxville near Farragut and we had ping pong to golf ball size hail at my house. I remember the Emergency Alert System on the tv constantly going off throughout the afternoon and evening.
There is an Enhanced risk for strong to severe thunderstorms in the Central and Southern Valleys, Mountains, and Northeast TN. There is a Slight risk for the Plateau.
Timing: 10 AM - 4 PM
Hazards: Damaging winds up to 70 mph is the primary threat. Large hail to quarter size or larger is also possible. An isolated tornado or 2 can't be rueld out.
There are a couple things that do make this severe threat conditional. Firstly, we'll have to see how fast the early morning rain and storms move out of the area. The longer the rain and clouds linger, the lower the severe risk will be. Also, we will have to keep our eye on any storms in Georgia. If there is a lot of convection down there in the late morning/early afternoon timeframe, those storms could prevent moisture transport to East TN, leading to a more stable atmosphere.
An active severe weather day is expected. The main driver of this
event will be a negatively-tilted trough with a strong vort max
that will be rotating around a closed upper low, and the
associated jet streak at the base of that trough. Over the next
few hours, we expect that convection will develop along and west
of I-75, where the RAP and HRRR show an axis of higher CAPE
values. We are already starting to see this development in NE AL
at the moment. This instability axis shifts east into the central
Valley during the early afternoon, and into NE TN/SW VA in the
late afternoon. Aloft, we will have a surge of dry and cooler air
aloft that will aid in destabilization by steepening midlevel
lapse rates. In the 12Z OHX sounding, we are seeing values of 7.5 C/km, which will be advecting east. Deep shear will be adequate
for supercells, and 0-1 km shear values and LCL heights suggest a tornado threat, mainly for areas south of I-40 and east of I-75.
However, it is notable that the HREF shows some updrafthelicity
tracks north of I-40 this afternoon, so a tornado threat can`t be
ruled out anywhere.
This initial round of storms between 11-4 pm are expected to
mainly pose a damaging wind threat with a lower threat of
tornadoes, then a second round is expected to develop in the mid
to late afternoon near the Plateau, which may be primarily a hail
threat as WBZ heights quickly drop as the closed upper low
approaches. The HRRR shows this second round crossing our area
between 4-8 pm.
DISCUSSION...Pockets of stronger heating in broken cloudiness, and
surface dewpoints mainly in the mid 60s F (low 60s F into western
NC/VA) are resulting in weak destabilization as of midday. Ongoing
showers and thunderstorms and thicker cloud cover across eastern KY
into VA/WV will slow airmass recovery and does lead to some
uncertainty in northward extent of the severe threat over the next
few hours. Where greater destabilization is occurring ahead of the
surface low (northern GA/eastern TN vicinity), thunderstorm coverage
and intensity is expected to increase over the next couple of hours.
Moderate vertical shear will support organized storm structures,
with clusters and bows being the primary storm mode expected this
afternoon, though a couple of more discrete supercells also will be
Fast storm motion and cluster/linear-type storm structures will
favor damaging wind potential. However, low-level vorticity will
increase as the surface low develops eastward across KY/TN.
Additionally, increasing wind speeds from the surface through 3 km
will support modestly enlarged low-level hodographs. Where stronger
destabilization can occur, a couple of tornadoes will be possible,
both with any semi-discrete cells or within developing bows/QLCS
structures. A watch will likely be needed for portions of the MCD
area in the next hour.