SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0252 PM CDT Sun Mar 12 2023
Valid 122000Z - 131200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTH-CENTRAL/NORTHEASTERN GULF COAST AND SOUTHERN GEORGIA...
...SUMMARY...
Severe hail, damaging winds and a couple tornadoes are possible
today across parts of the Southeast. A few strong/severe storms are
also possible in the California Central Valley.
...20Z Update...
...Southeast...
Thunderstorms continue along the outflow boundary currently extended
from near SAV southwestward across southern GA into the central FL
Panhandle. Environmental conditions will continue to support strong
to severe thunderstorms capable of hail, damaging gusts, and/or a
brief tornado for the next few hours before diminishing amid limited
buoyancy across northern FL.
Additional thunderstorms have developed along the front from far
northeast into southwest/south-central MS. Widespread cloud cover
continues to limit buoyancy ahead of this front, but ample low-level
moisture remains in place and thunderstorms are expected to
continue. Moderate vertical shear also persists across the region,
supporting the potential for a few stronger, more organized updrafts
capable of hail and/or damaging gusts.
...Central CA...
Isolated thunderstorm development will continue across the region
for the next several hours, supported by persistent forcing for
ascent and modest low/mid-level moisture. Deep layer vertical shear
is strong enough to support supercells with any mature/persistent
convection. Marginally severe hail is the primary risk, but a brief
tornado or two is also possible.
..Mosier.. 03/12/2023
.PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Mar 12 2023/
...Synopsis...
In mid/upper levels, a progressive pattern is forecast to continue
across the CONUS, characterized by
1. Essentially conjoined northern and southern streams, and
2. Lower-amplitude perturbations with southward extent, amidst
nearly zonal flow.
The most intense features -- a cyclone/trough now over MN and
another over the Pacific well west of Vancouver Island -- will
remain removed from areas of potentially strong-severe convection.
Instead, to their south, a series of vorticity maxima and weak
shortwaves will traverse the westerlies from offshore of CA, across
CA/NV/AZ to the southern Rockies and southern Plains, to the TN
Valley and Gulf Coast States.
At the surface, an occluded low was analyzed at 15Z near the eastern
portion of the KY/TN line, with occluded/cold front southwestward
across northern AL, western MS, central LA, and south-central TX. A
warm front was drawn across parts of southern SC and south-central
GA to southeastern AL, where it was being overtaken by convective
outflow. The latter process will continue, as the bulk of
surface-based convection should remain well ahead of the cold front.
By 00Z, the cold front should reach from a triple point over
western GA across southern AL to southeastern LA, then across
extreme southeastern GA and northwestern FL by 12Z.
...Southeast...
Scattered thunderstorms are expected to occur along and behind a
progressive, aggregate outflow boundary that is evident across
south-central GA, southern AL and extreme southern MS. Large hail,
damaging gusts and a couple tornadoes are possible. Refer to SPC
mesoscale discussion 280 for the near-term scenario. The progress
of this boundary -- and the trailing area of stabilizing precip --
has reduced severe potential from the northwest, and outlook lines
have been adjusted accordingly. However, as the boundary and
associated convection move into a destabilizing environment across
parts of southern MS/AL/GA and the FL Panhandle, a gradual increase
in severe potential is possible through early afternoon. This will
be supported by a combination of low-level theta-e advection --
which will warm/moisten parts of southern GA now under the
more-stable influence of drier FL Peninsular trajectories -- and
cloud-tempered diabatic surface heating.
Peak/preconvective MLCAPE around 1500 J/kg should spread/expand
eastward across the remaining parts of the outlook area through the
afternoon, while the outflow continues to shunt the western bounds
of substantial severe potential southeastward. Modified RAOBs and
forecast soundings indicate 40-50-kt effective-shear vectors,
aligned nearly parallel to the middle/western parts of the outflow
boundary, and slightly across it over the eastern (currently
southeastern AL/GA) section. This will occur amidst broadly
difluent mid/upper-level flow and subtle shots of DCVA from
aforementioned minor southern-stream perturbations. As such,
episodic but gradual net increase in convective intensity/coverage
appears to be supported into the afternoon, over the remaining areas
ahead of the boundary. Potential should diminish this evening in
step with decrease of lift and available inflow-layer instability.
...Central CA...
Widely scattered to scattered thunderstorms should cross the region
during mid-late afternoon, offering a marginal hail and tornado
threat. Activity will be supported by destabilization from a
combination of cold midlevel temperatures and gradual diurnal
heating. This will reduce already meager MLCINH and support
relatively deep for this area (300-350-mb equilibrium levels) MLCAPE
in the 500-1000 J/kg range. With near-surface flow weak, but backed
due to orographic forcing, sufficient veering of modest low-level
winds with height will be present to contribute to 35-40 kt
effective-shear magnitudes. Hodographs are not forecast to be
particularly large, but will be well-curved, with at least
marginally favorable deep shear to support potential for a few
supercells to mature across the valley before weakening deeper into
in the foothills/Sierra.
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