SPC AC 061248

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0748 AM CDT Tue Jun 06 2023

   Valid 061300Z - 071200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   THE INTERMOUNTAIN WEST...SOUTHERN ROCKIES TO FAR WEST TEXAS...SOUTH
   FLORIDA...AND CAROLINAS...

   ...SUMMARY...
   Isolated strong to severe thunderstorm gusts and hail are expected
   today over parts of the Intermountain West, southern Rockies to far
   west Texas, south Florida, and Carolinas.

   ...Synopsis...
   In mid/upper levels, a blocking pattern will remain in place through
   the period, as in previous days, anchored by a stout mean ridge up
   and down the Great Plains, with a high over the northern Plains. 
   This period, the high will weaken and shift westward very slightly,
   as a synoptic cyclone now centered over coastal NS retrogrades
   northwestward toward northeastern ME.  That, along with a series of
   shortwaves pivoting through the western flow field of the cyclone,
   will lead to a broad area of height falls from the Great Lakes
   across the Appalachians to much of the Atlantic Coast.  A
   subtropical jet in upper levels will extend from central MX across
   the southern Gulf and Yucatan, to the Keys and south FL, south of a
   lingering field of cyclonic flow covering the Gulf Coast States and
   much of the northern Gulf.

   Farther west, a 500-mb low now over the SBA area will drift
   erratically through the period, with very slight eastward motion
   possible into more of southern CA through the period.  Associated
   mid/upper difluence, between the cyclone's eastern northern rim and
   the mean ridge, will cover much of the Rockies and Intermountain
   West.  A weak, quasistationary trough aloft will extend across the
   central Rockies/Plains and Arklatex to the Gulf of Mexico troughing.

   At the surface, 11Z analysis showed a cold front over Atlantic
   waters east of the Delmarva Peninsula, decelerating to
   quasistationary across northern/western NC, the length of TN, and
   northern parts of AR/OK.  The boundary over and east of the
   Appalachians will move southward again today as a cold front,
   beneath the height falls aloft.  Farther west, a dryline has backed
   well into the higher terrain of central/northern MX and
   southern/central NM.

   ...Intermountain West...
   Widely scattered thunderstorms are expected to develop across
   southern parts of this region and fan northward out of northern UT,
   and northwestward to westward out of northern NV, amid the strong
   difluence.  Isolated severe gusts and hail near severe limits are
   possible, despite a lack of substantial deep shear.  A belt of
   low-level trough/convergence along the outlook corridor, with local
   orographic and diurnal-heating support, will contribute to lift over
   the region.  Deep/well-mixed subcloud layers should develop over
   lower elevations, with very steep lapse rates, and enough remaining
   moisture to support areas of 500-1000 J/kg MLCAPE, with even larger
   DCAPE values evident in forecast soundings.  Associated "inverted-V"
   thermodynamic profiles will support deep downdraft
   cooling/accelerations in the most intense cells.

   ...Southern Rockies to far west TX...
   Isolated to scattered thunderstorms are expected to develop this
   afternoon, predominantly over higher terrain on either side of the
   Rio Grande Valley in NM, and southeastward across parts of far west
   TX and adjoining Chihuahua.  Strong/isolated severe gusts and hail
   are possible for a few hours into early evening, before a
   combination of environmental diabatic cooling and spreading outflow
   air curtail the convection.  Activity should form amid strong
   heating and favorable moisture at high elevation, then move eastward
   into adjoining valleys where 500-1000 J/kg MLCAPE and deeply mixed
   subcloud layers can support strong downdraft production/
   acceleration.  Organization of the activity will be limited by lack
   of vertical shear; however, some forward-propagational clustering
   may boost severe potential on small scales.

   ...SC/NC...
   Isolated to scattered thunderstorms are expected to develop along/
   ahead of the front from eastern SC southwestward over SC, beneath
   the southwestern rim of stronger cyclonic flow aloft related to the
   major/retrograding low over western parts of the Canadian Maritimes.
   The most intense cells will be capable of damaging, perhaps
   marginally severe gusts, as well as isolated hail near severe
   limits.  An eastward-tapering corridor of favorable low-level
   moisture and strong diurnal heating will develop ahead of the front
   and west of the sounds over SC and parts of central/southern NC,
   supporting MLCAPE in the 1500-2000 J/kg range atop steep low-level
   lapse rates and a suitably deep, well-mixed boundary layer for
   downdraft acceleration.  Vertical shear will be weak except through
   the entire cloud-bearing layer, given the majority westerly
   directional wind component throughout the troposphere.

   ...South FL...
   Scattered thunderstorms will form through afternoon as outflow from
   ongoing convection, as well as the Gulf and Atlantic sea breezes
   penetrate inland and interact, and on subsequent outflow boundaries
   and intersections.  The most intense cells will be capable of severe
   hail or damaging to marginally severe gusts from water-loaded
   downdrafts.  Strong diurnal heating and rich low-level moisture
   (e.g., surface dewpoints commonly in the low 70s F), along with weak
   MLCINH, will offset modest mid/upper-level lapse rates in supporting
   development, with preconvective MLCAPE reaching as much as 2000 J/kg
   locally.  Although near-surface flow and boundary-layer shear should
   be weak overall, the presence of light easterlies under the
   subtropical jet will lead to somewhat favorable deep/cloud-layer
   shear for convective organization.  Activity should weaken
   substantially late afternoon into evening with outflow spread and
   diabatic surface cooling.

   ..Edwards/Smith.. 06/06/2023

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z