LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Mon Jul 31 2023
Valid 311300Z - 011200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE NORTHERN/CENTRAL PLAINS...COASTAL SOUTHEAST...LOWER MISSOURI
VALLEY TO WEST-CENTRAL GULF COAST...AND ARIZONA...
...SUMMARY...
Isolated severe thunderstorms are possible over portions of the
northern/central Plains, coastal Southeast, lower Missouri Valley to
west-central Gulf Coast, and Arizona.
...Synopsis...
In mid/upper levels, the center of a persistent anticyclone has
shifted eastward slightly, from the Four Corners and southern
Rockies regions to the south-central High Plains. This has occurred
as a series of small shortwaves and accompanying convectively
induced/enhanced vorticity maxima pivot northwestward out of MC,
then northward around the western rim of the circulation. The
northern few of that series will pivot northeastward across the
northern/central Rockies and adjoining High Plains through this
period.
A synoptic-scale ridge will continue to extend east-southeastward
from the high across the Arklatex/Mid-South region, temporarily
penetrated by a prominent MCV and accompanying shortwave trough now
over AR. This perturbation is progged to deamplify today as it
moves southward into a regime of weakening, difluent ambient flow,
but still may contribute to convection to its south and southeast
(see below). Meanwhile, a small shortwave trough -- apparent in
moisture-channel imagery over KY -- is expected to move quickly
southeastward to the southern part of a large-scale trough over the
Carolinas and GA, during the 00-06Z time frame.
The 11Z surface analysis showed a low near GSO with quasistationary
frontal zone southeastward across southern SC and southwestward over
northern portions of GA/AL/MS. The frontal zone was interrupted by
MCS cold pools across AR, MO and NE, but the associated
baroclinicity should become better defined again later today, in a
southeast/northwest fashion across those areas, as the outflow
becomes shallower/weaker.
...Northern/central Plains...
Isolated to locally scattered thunderstorms are expected to develop
this afternoon from the eastern ranges/foothills of the Rockies to
the frontal zone, and along residual surface boundaries in between.
Isolated severe hail/gusts are possible.
The environment for this activity will be characterized by adequate
low-level moisture (surface dewpoints generally in the 50s and lower
60s F), steep low-level lapse rates with well-mixed sub cloud
layers, and in he central High Plains, relatively weak shear but
strong heating/mixing. A conditional risk for significant (2+ inch
diameter) hail exists over the northern Plains part of the outlook
area, where favorable vertical shear for supercells again is
expected in and near the frontal zone. Southeast flow near the
surface, veering sharply with height to the northwesterly and
westerly winds aloft, will result in wind profiles characterized by
small 0-1-km SRH but long hodographs, and effective-shear magnitudes
in the 40-50-kt range. However, with generally rising heights aloft
and subtle low-level forcing, placement and coverage is uncertain,
with at least an isolated supercell or two possible almost anywhere
in the corridor.
...Lower Missouri Valley to west-central Gulf Coast...
An outflow boundary preceding the southern MCV is moving southward
through LA, with the bulk of convection elevated over the still-
progressive cold pool behind it. However, as the boundary
encounters diurnally destabilizing, very moist Gulf air through the
afternoon, additional, surface-based convection may form along it
and produce strong to isolated severe gusts. Activity should remain
multicellular in character, given the weak ambient shear.
That outflow boundary moved well into eastern central OK and
northeast TX; however, the air mass across the western and later the
remainder of the outlook area may recover with warm/moist advection
from a narrow corridor of relatively maximized moisture across
central OK into central/eastern KS, near the morning boundary.
Though not as high-theta-e as the relatively undisturbed air mass
farther southeast near the Gulf Coast, moisture and diurnal
destabilization ahead of the NE MCV/precip may support additional
strong to locally severe thunderstorms this afternoon into tonight
over the lower Missouri Valley to Ozarks. A 30-35 kt southwesterly
LLJ overnight, beneath steep lapse rates and northwest flow in
midlevels, also may foster sufficient moisture and effective shear
to support hail potential over northern parts of the outlook area,
as parcels rise isentropically to an LFC, along an elevated segment
of the baroclinic zone.
...Coastal Southeast...
Widely scattered to scattered thunderstorms should form along/ahead
of the surface front today over portions of the Carolinas and GA,
becoming scattered to numerous amid an active sea-breeze/outflow-
boundary regime over the central/eastern FL Peninsula. Frontal lift
is expected to be modest, given the presence of light winds with
northerly component ahead of it. Still, even weak frontal lift,
along with diurnal heating, should suffice to initiate convection
over northern parts of the outlook area, with subtle large-scale
support for the environment aloft preceding the approaching
shortwave trough. The entire corridor will be characterized by
pockets of strong diurnal heating amidst rich low-level moisture,
with dewpoints commonly in the upper 60s to mid 70s F, along with
high PW. Weak deep-layer wind profiles and related lack of shear
should limit overall organization, with damaging to isolated severe
gusts the main concern in the most intense multicells.
...AZ...
Isolated severe gusts will be possible this afternoon into evening
as convection moves over the well-heated/mixed desert boundary
layer. One prominent midlevel perturbation in the aforementioned
chain of them should move away from the area today. Though
large-scale lift will not be as strong as the previous day,
sustained heating should occur behind morning clouds/precip over the
southeastern CA/southwestern AZ region. This will support scattered
thunderstorms development this afternoon, initially over the higher
ranges in southeastern AZ and parts of the Mogollon Rim. A more
southerly mean-flow component today behind the trough will encourage
northwestward cell motion, with perhaps some westward curvature
where outflow pools accrete. MLCAPE values of 500-1000 J/kg
(locally higher) and even larger DCAPE will support gust potential.
..Edwards/Broyles.. 07/31/2023
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