SPC AC 071248
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Wed Jun 07 2023
Valid 071300Z - 081200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN HIGH PLAINS...NORTHWEST...NORTHEASTERN PLAINS...LOWER
TO MID MISSOURI VALLEY...COASTAL CAROLINAS...AND FLORIDA...
...SUMMARY...
Marginally severe thunderstorms, associated with strong winds and
hail, will be possible today across parts of the southern High
Plains, Northwest, northeastern Plains, lower to mid Missouri
Valley, coastal Carolinas, and Florida.
...Synopsis...
Another day of large-scale blocking aloft will characterize the
mid/upper-level pattern, with mean ridging over the central CONUS
and a large, zonally elongated cyclone over the Northeast, Great
Lakes and much of the East Coast. The associated 500-mb low is
expected to retrograde slowly westward from its present position
over NB, across ME toward the northern fringes of NH/VT through the
period.
A weak 500-mb high remains over the northern Plains, anchoring the
mean ridge, while a quasistationary trough/height weakness persists
from the central Rockies southeastward over the southern High
Plains, and across the mean ridge to south TX. This is connected
loosely to an area of cyclonic flow over the central Gulf, which
includes a weak shortwave trough, from the Gulf north of the Yucatan
Channel south-southwestward over the Yucatan peninsula. This
perturbation should move east-northeastward over portions of
central/south FL by 00Z. Meanwhile, a mid/upper-level low over
south-central CA will weaken slowly and drift eastward toward the
TPH-LAS vicinity by 12Z tomorrow.
At the surface, 11Z analysis showed a quasistationary to slow-moving
cold front over the southern Delmarva Peninsula, southern WV, and
northern KY, curving northwestward across southern IL, northeastern
MO, northwestern IA, and extreme eastern ND. The segment of this
boundary east of the Blue Ridge should move southward across the
remainder of VA and into NC buy the end of the period. Another,
preceding front was drawn across coastal NC and central SC, and
should shift southeastward through the day as well.
...Coastal Carolinas and vicinity...
Widely scattered to scattered thunderstorms should develop this
afternoon near the leading front, with isolated development possible
to its south. Associated multicells should move eastward to
southeastward over the outlook area, offering damaging to marginal
severe gusts and isolated hail. Although the westerly/front-
parallel flow component at the surface will limit both low-level
shear and frontal convergence, MLCINH should be weak, allowing even
reduced lift to support convective initiation. Favorable low-level
moisture is expected, with 60s F surface dewpoints and diurnal
heating underlying -11 to -12 deg C 500-mb temperatures in the
southern rim of the broad cyclonic-flow field aloft. The result
should be around 1000-1500 J/kg MLCAPE -- locally/briefly higher --
with 25-35-kt effective-shear magnitudes.
....FL...
Scattered thunderstorms should develop from midday through afternoon
along sea-breeze boundaries, as well as subsequent outflow
boundaries and their intersections. The West Coast boundary should
be displaced well eastward/inland before the bulk of its convection
forms, given the predominantly westerly boundary-layer wind
component. Strong surface heating and rich moisture -- with
dewpoints commonly in the upper 60s to low 70s F -- will underlie a
deep troposphere and strong anvil-level flow related to the
subtropical jet. Subtle large-scale ascent ahead of the Gulf
perturbation also will contribute to a convectively favorable
environment in this area. A few organized multicells with hail
and/or water-loaded downdrafts are possible, before activity
diminishes in the evening due to expansive outflow and nocturnal
cooling.
...Lower to Mid Missouri Valley/Northeastern Plains...
A narrow plume of favorable moisture and lift near the front will
contribute to potential for widely scattered thunderstorms mainly
this afternoon. Isolated, marginally severe gusts and hail are
possible. The moist plume should be characterized by surface
dewpoints often remaining in the 60s F today, even through diurnal
heating/mixing of the boundary layer. This should offset modest
mid/upper-level lapse rates enough to support around 800-1500 J/kg
MLCAPE, atop steep low-level lapse rates. Weak deep-layer winds/
shear will be present, but the low-level thermodynamic profile
should support maintenance to the surface of some strong-severe hail
and downdrafts.
...Southern High Plains to Big Bend...
Scattered thunderstorms are expected to develop again today across
this region, offering marginally severe gusts and hail from the most
intense cores. A strongly heated and favorably moist boundary layer
will underlie only weak MLCINH, under an EML that remains poorly
developed for the time being. Still, steep low/middle-level lapse
rates of 8-8.5 deg C/km are forecast, combining with mid 40s to mid
50s F surface dewpoints at 4000+ ft MSL elevations of the western
parts of the outlook area, to yield MLCAPE in the 1500-2500 J/kg
range. Proximity to the upper ridge will keep deep-layer flow and
shear weak over most of the region, though the prevailing/light
westerly component should encourage eastward movement (and perhaps
some clustering and cold-pool organization on smaller scales).
Enough deep shear may persist across the Davis Mountains/Big Bend
region -- under the north rim of the subtropical jet -- to support a
right-moving supercell or two, with a conditional risk of isolated
significant hail. Severe potential may persist across the lower
Pecos Valley and Permian Basin of west TX, as well as South Plains
and western Panhandle farther north, before the nocturnal weakening
of this convection.
...Interior Northwest...
With a rather stagnant upper pattern and similar to slightly greater
low-level moisture over the area compared to yesterday, another
round of isolated to scattered afternoon thunderstorms is expected
to develop under strong difluence aloft to the northeast of the CA
cyclone. Development will be supported by moisture equivalent to
50s surface dewpoints at lower elevations, along with diurnal
heating (especially over windward slopes). Convection should fan
out mostly northward over eastern parts of the outlook area and
northwestward to westward elsewhere, offering strong/isolated severe
gusts through a well-mixed subcloud layer characterized by steep
lapse rates. Isolated hail near severe limits also cannot be ruled
out.
..Edwards/Smith.. 06/07/2023
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