SPC AC 311956
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0256 PM CDT Wed Oct 31 2018
Valid 312000Z - 011200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
TEXAS TO SOUTHWEST MISSISSIPPI...
...SUMMARY...
The greatest risk for severe thunderstorms, capable of producing
damaging winds, hail, and tornadoes, exists from southeast Texas to
the lower Mississippi Valley through tonight.
...Discussion...
Have removed severe probabilities from portions of the Big Country
into north Texas, where the south/southeastward progression of a
cold front and an expansive trailing precipitation shield are likely
minimizing any severe threat. Additionally, Marginal probabilities
have been extended westward towards El Paso, where forcing for
ascent with the primary shortwave impulse may continue to support a
localized hail/wind threat.
Otherwise, a greater tornado/damaging wind potential is still
expected to materialize late this evening into tonight from
southeast Texas to the lower Mississippi Valley, and no changes have
been made to the ongoing probabilities here. For more information on
this threat, see the previous discussion below.
..Picca.. 10/31/2018
.PREV DISCUSSION... /ISSUED 1129 AM CDT Wed Oct 31 2018/
...TX today to LA/MS overnight...
A midlevel shortwave trough now near El Paso will continue eastward
across TX through tonight. Weak cyclogenesis is expected by this
evening and continuing through tonight, along a pre-existing front
from central TX to the Mid South. A moist low-level air mass is
already present south of the front, with low 70s boundary-layer
dewpoints spreading across the northwest Gulf coast. Gradual mass
response to the cyclogenesis will result in strengthening low-level
flow/shear, especially tonight across LA/MS.
Ongoing convection in TX has largely remained elevated atop the
frontal surface, but may gradually transition to surface-based
storms along the front later this afternoon. Isolated strong-severe
storms will also be possible this afternoon/evening into southwest
TX, along the west edge of the richer low-level moisture and in the
zone of stronger low-midlevel ascent preceding the shortwave trough.
Farther east, the ongoing warm sector convection across the upper TX
coast should persist through the afternoon and spread slowly
eastward/northeastward. Additional warm sector storm development is
also expected tonight along the moist axis into southern LA.
Wind profiles are only marginally favorable for organized/supercell
storms at present across TX, with slow strengthening of vertical
shear expected later this afternoon through tonight farther east
toward the lower MS Valley. A few supercells could evolve from the
ongoing upper TX coast convection, as well as embedded
supercells/bowing segments along the front from central into east
TX. This frontal convection will likely evolve into a line that
will move eastward overnight, with an accompanying threat for
damaging winds and a couple of tornadoes with embedded circulations.
The more substantial supercell/tornado threat is expected overnight
into parts of LA (and possibly MS) within the moist sector, and
where low-level shear becomes the strongest. A strong tornado or
two will be possible, especially with any pre-frontal supercell
clusters, where effective SRH increases to greater than 400 m2/s2 in
a moist environment with sufficient surface-based buoyancy.
Tornado Outlook
Strong Wind Outlook
Hail Outlook
Severe Thunderstorm Outlook
