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
updraft helicity
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.