Mesoscale Discussion 0370
NWS Storm Prediction Center Norman OK
0550 PM CDT Wed Mar 29 2017
Areas affected…Portions of LA…western MS…southeast AR
Concerning…Tornado Watch 98…
Valid 292250Z – 300045Z
The severe weather threat for Tornado Watch 98 continues.
SUMMARY…The risk for severe thunderstorms and tornadoes continues across Tornado Watch 98, and will spread east-northeastward and northeastward through the evening and overnight hours. An additional Watch will likely be required prior to the 02Z expiration of Watch 98.
DISCUSSION…Clusters of thunderstorms, including embedded rotating updrafts and bowing segments, continue in the vicinity of the lower Sabine Valley. Inflow for this activity is characterized by around 500-2000 J/kg of MLCAPE (higher buoyancy amid richer moisture with southward extent), based on modifications to the 18Z Lake Charles
and Shreveport observed soundings. This activity lies within the warm sector of a broader extratropical cyclone, within which modest positive theta-e advection will continue during the next several
hours.
As a result, convection will continue to spread east-northeastward and northeastward into the evening and overnight hours. This will occur while ascent attendant to the right-entrance region of a midlevel speed maximum encourages both (1) the maintenance of at least modest instability, and (2) a low-level mass response supporting moderate low-level shear and isentropic ascent. Moreover, with 40-55 kt of effective shear attendant to the speed maximum, organized convective modes will continue to be favored.
While damaging winds and sporadic severe hail will be the primary concerns with this activity, tornado potential will exist with embedded supercell structures and meso-vortices. This would especially be the case as strengthening low-level shear juxtaposes increasing boundary-layer theta-e through the night. Accordingly, a new watch will likely be issued from parts of southern LA to the ArkLaMiss region prior to the expiration of Tornado Watch 98.
