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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