Mesoscale Discussion 1121
NWS Storm Prediction Center Norman OK
1150 AM CDT Thu Jun 22 2017
Areas affected...Central/eastern LA...Central/southern
MS...Southeast AR...Central/southern AL...FL Panhandle
Concerning...Tornado Watch 363...
Valid 221650Z - 221815Z
The severe weather threat for Tornado Watch 363 continues.
SUMMARY...Isolated tornado threat continues east of Tropical
Depression Cindy. New watch issuance is likely before 18Z.
DISCUSSION...Thus far this morning, the strongest convection (and
occasional rotation) has been noted across the eastern portion of WW
363, with a possible waterspout/tornado reported earlier this
morning near Pensacola. This region is located within the strong
belt of deep, moist southerly flow to the east of a well-defined
midlevel dry slot that is wrapping into TD Cindy. While wind
profiles are southerly through a deep layer, backing of the
low-level flow is supporting substantial low-level shear, with 0-1
km shear of 25-35 kts noted per recent mesoanalyses and VWP data.
Very warm midlevel temperatures and poor lapse rates will continue
to limit the intensity of convection through the day, but the the
strongest cells will pose an isolated tornado threat given the
aforementioned low-level shear magnitude coincident with a very
moist, tropical airmass and potential for some additional
destabilization as modest heating continues. Some threat may spread
north out of the watch by early afternoon, though it is unclear at
this time whether any northward expansion of the watch will be
Further east, closer to the primary circulation of TD Cindy,
convection has likely been inhibited by very dry midlevel air noted
on WV imagery. However, greater insolation within the dry slot has
allowed stronger heating to occur, and convection has begun to
gradually increase across southern/eastern LA and southern MS.
Continued destabilization within a low-level environment that is
very moist and strongly sheared will support a gradual increase in
the tornado threat through the day across portions of LA into
Since some tornado threat is likely to persist through the afternoon
across WW 363, a new tornado watch will likely be required before
18Z covering generally the same area from LA eastward through MS,
and perhaps northward into southeast AR and eastward into portions
of AL and the FL Panhandle.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 29169219 33569220 33508875 33198598 30788599 29698617
29538846 28458880 28599111 29169219