SPC AC 181732

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1232 PM CDT Fri Jun 18 2021

   Valid 191200Z - 201200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE
   NORTHERN GULF COAST AND THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Widely scattered severe thunderstorms will be possible Saturday
   afternoon through the evening across the central High Plains.  A
   couple of tornadoes are possible over the northern Gulf Coast.

   ...Central High Plains...
   An upper trough is forecast to gradually amplify across the northern
   Rockies/northern High Plains through the period.  A lead mid-level
   speed max over MT late Saturday afternoon will move into the Dakotas
   by early Sunday morning.  At the surface, a lee trough will likely
   develop by Saturday afternoon over much of the northern and central
   High Plains.  A cold front should surge southeastward across the
   western Dakotas overnight as a surface low develops eastward
   along/near the NE/SD border.  

   Strong diurnal heating and appreciable low-level moisture will yield
   MLCAPE ranging from 500 J/kg near the Front Range to 2500 over
   southwest NE/northwest KS.  Isolated to scattered storms will
   initially develop over the higher terrain and along the lee trough
   Saturday afternoon.  As this activity moves into richer low-level
   moisture and greater buoyancy, additional storms will develop with
   cold pools coalescing with time.  The early activity will
   potentially pose a risk for hail/wind before upscale growth into a
   MCS occurs during the early evening.  The steep low- and mid-level
   lapse rates will favor efficient downdrafts with severe gusts near
   the heavier precip-laden cores.  The 12z CAMs have shown a rather
   strong signal for a linear cluster/MCS over northeast CO moving into
   adjacent parts of KS/NE during the evening into the overnight.  It
   is the combination of the favorable linear mode (as depicted in
   models), steep lapse rates, and sufficient deep shear that fostered
   higher-than-average confidence for an upgrade to 15-percent wind
   probabilities this forecast update.  

   ...Central Gulf Coast...
   A potential tropical cyclone is forecast by the National Hurricane
   Center to move northeastward and affect parts of the central Gulf
   Coast on Saturday.  A rich low-level airmass with low 70s surface
   dewpoints will spread inland across the northern Gulf Coast to the
   east of the center of the circulation by Saturday afternoon. Strong
   low-level shear is expected in the eastern half of the circulation
   as 45-55 kt of southerly flow at 850 mb will likely be present. 
   This will result in favorable hodographs and a conditional risk for
   low-level rotation with any robust updraft that can form where
   boundary-layer destabilization is sufficient to support
   surface-based storms.  The risk for a couple of tornadoes will
   probably peak coincident with destabilization/diurnal heating cycle
   but the risk could persist into parts of central AL and southwestern
   GA Saturday evening/night.

   ...Ohio Valley into the Mid-Atlantic and Northeast...
   An upper trough with strong mid-level westerlies is expected to move
   eastward across the Great Lakes, OH Valley, Mid-Atlantic, and
   Northeast on Saturday.  A surface cold front should develop eastward
   across the Northeast through the day, with the trailing portion of
   this front likely stalling and becoming oriented more east-west
   across the OH Valley.  There is relatively large uncertainty for
   this forecast for much of this region due largley in part to
   shower/thunderstorm development late Friday night and into Saturday
   morning influencing the magnitude of destabilization.  Some guidance
   continues to suggest that robust destabilization may occur in its
   wake from parts of central/eastern IL into IN/OH, southern Lower MI,
   and perhaps western PA and WV.  This corridor appears to have the
   most favorable overlap of forecast moderate to strong instability
   and deep-layer shear for organized storms Saturday afternoon. A mix
   of supercells and clusters posing a threat for large hail, damaging
   wind gusts, and perhaps a tornado or two may focus along/south of
   the cold front. 

   Farther northeast, isolated strong to locally severe storms may
   develop along/east of the cold front from northern PA into the
   Northeast through the day.  Instability is forecast to be somewhat
   more limited across this region compared to locations farther
   south/west into the Mid-Atlantic and OH Valley where greater
   low-level moisture should be present. Still, strong effective bulk
   shear around 40-50 kt will likely support organized updrafts even if
   the instability remains fairly weak.  Isolated instances of
   marginally severe hail and strong/damaging winds should be the main
   threat with these storms before they weaken and/or move offshore
   Saturday evening.

   ..Smith.. 06/18/2021

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z