Mesoscale Discussion 0221
NWS Storm Prediction Center Norman OK
0528 PM CST Tue Feb 28 2017
Areas affected...Central Arkansas into southeast Missouri
Concerning...Tornado Watch 43...
Valid 282328Z - 010130Z
The severe weather threat for Tornado Watch 43 continues.
SUMMARY...The threat for tornadoes may increase over the next few
hours across Arkansas into southeastern Missouri, with further
development into the lower Ohio Valley and western Tennessee later
DISCUSSION...Multiple clusters of thunderstorms continue to evolve
across central Arkansas into southern Missouri across the open warm
sector and driven mainly by warm advection in the low levels and
lack of substantial capping.
Cells over Missouri have shown complex storm structures, with
several splits noted on radar. This is not surprising given the
mainly straight-line hodograph on the 20Z observed SGF sounding.
Also evident steep lapse rates and strong deep-layer shear, which
support a severe hail threat. As these storms continue eastward,
they will encounter a more unstable and more sheared environment
supported by a gradually increasing low-level jet and observed axis
of mid 60s dewpoints in place. Therefore, potential for stronger
rotation and right-moving tornadic supercells will increase over
To the south, 850-mb flow is a bit stronger and more backed, with a
cluster of cells west of the Little Rock area showing mesocyclones
at times, but nothing long-lived thus far. However, the LZK VWP as
well as objective analysis indicate 250-300 m2/s2 0-3 km SRH in
place, with an upward trend in GPS PW observations as well. The
increasing low-level jet will further increase low-level shear this
evening, favoring tornadic supercells.
Model guidance suggests increasing storm coverage spreading eastward
across the lower Ohio Valley and western Tennessee, with a risk of
tornadoes this evening. As such, additional tornado watches could be
required in those areas.
LAT...LON 34369315 34039392 34279444 34489440 37309252 37988947
37898867 37448838 36818839 36008886 35348933 34959014