Mesoscale Discussion 1106
NWS Storm Prediction Center Norman OK
0212 AM CDT Wed Jun 21 2017
Areas affected...Portions of the central Gulf Coast
Concerning...Tornado Watch 358...
Valid 210712Z - 210915Z
CORRECTED FOR WATCH TYPE
The severe weather threat for Tornado Watch 358 continues.
SUMMARY...The threat for a few tornadoes along the central Gulf
Coast should continue to slowly increase towards daybreak.
DISCUSSION...As Tropical Storm Cindy continues its slow
northwestward movement, a broad area of showers and thunderstorms
has advanced near/onshore from Louisiana eastward to the Florida
Panhandle. Several convective cells (primarily those offshore)
within this regime have exhibited low-level rotation, with
occasional waterspouts probable in several of these offshore cells.
Regional VWP data (e.g., KLIX, KMOB, KEVX) sample low-level winds
strongly veering with height, bolstering storm-relative helicity and
the potential for low-level mesocyclogenesis. Additionally, this
notable veering implies considerable warm-air advection near a front
stretching from Plaquemines Parish east/northeastward to the Florida
Panhandle. Near and to the south of this boundary, dew points in the
mid/upper 70s and temperatures in the upper 70s/lower 80s are
offering adequate surface-based buoyancy for a tornadic threat.
VWP data, model analyses, and surface pressure-fall observations
indicate the strongest branch of the low-level jet currently resides
from the Alabama Panhandle southeastward into the Gulf. Indeed,
radar data indicate a band of strong thunderstorms extending
near/along this axis, likely fostered by warm-air advection and
speed convergence near the coast. While these cells are currently
displaced from zones of sufficient onshore destabilization (i.e.,
Plaquemines Parish, LA and the Apalachicola, FL vicinity), continued
northward advection of warm/moist air will likely increase the
tornado threat from southern Mississippi to the western Florida
Panhandle over the next several hours. Farther west, water-vapor
imagery and forecast soundings suggest drying aloft is leading to
shallower/more sparse convection across southeast Louisiana.
However, further surface destabilization and favorable
storm-relative helicity will maintain some tornado threat here as
well through the night.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 28949102 29299134 29989127 30519081 30918853 31038626
30898567 30278529 29718530 29448565 29588727 29088876