SPC AC 120551

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1251 AM CDT Sun Jul 12 2020

   Valid 121200Z - 131200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   EASTERN COLORADO...NORTHEAST NEW MEXICO...AND PARTS OF THE OKLAHOMA
   AND TEXAS PANHANDLES...

   ...SUMMARY...
   Isolated to widely scattered severe thunderstorms are forecast this
   afternoon through the late evening across parts of the central and
   southern High Plains.  Severe gusts and large hail are the primary
   hazards.

   ...Synopsis...
   A mid-level anticyclone will remain over the Desert Southwest today
   with a mid-level shortwave trough moving through the base of a
   larger scale trough over the eastern third of the U.S.  A
   disturbance is forecast to move across the northwestern CONUS during
   the period.  A few remnant MCVs originating from early morning
   thunderstorm activity may serve as features focusing
   showers/thunderstorms.  In the low levels, a composite front/outflow
   will become draped from the Arklatex westward across the southern
   Great Plains and extend north in lee of the central Rockies.  A
   surface low and associated lee trough are forecast to develop over
   the parts of the northern High Plains.

   ...Central-southern High Plains...
   Forecast model guidance indicates a weak disturbance will move
   through the central Rockies during the day and into the
   south-central High Plains late.  Strong heating and appreciable
   boundary layer moisture (surface dewpoints in the 50s near I-25 to
   the 60s over far eastern CO), will contribute to strong
   destabilization.  Easterly upslope flow veering to
   west-northwesterly will result in 25-45 kt effective shear. 
   Forecast soundings over southeastern CO show large CAPE in the -10
   to -30 deg C layer.  Supercells and severe multicells will be the
   preferred storm mode with a cluster or two likely evolving as
   outflow mergers lead to storms developing south-southeast into the
   OK/TX Panhandles during the evening.  

   ...East TX into the lower MS Valley...
   Overnight thunderstorm activity over parts of the southern Plains
   will move south into a moisture-rich boundary layer over the Sabine
   Valley during the morning.  It is uncertain whether a risk for
   damaging gusts will persist into the early morning over the
   northwest Gulf Coast.  With that stated, additional storms may
   develop during peak heating farther east over the lower MS Valley
   within a weakly capped airmass.  Isolated downbursts capable of wind
   damage are the primary severe threat.  

   ...OH Valley and central-southern Appalachians...
   Convective outflow from thunderstorm activity prior to the period
   will lead to some uncertainty regarding the quality of the airmass
   across parts of the OH Valley ahead of the mid-level disturbance. 
   Nonetheless, isolated to scattered thunderstorms are forecast to
   develop by early afternoon and gradually spread east/downstream
   across parts of the central-southern Appalachians during the
   afternoon/early evening.  Moderate destabilization/deep-layer shear
   will likely result in organized storm structures with isolated
   damaging gusts/marginally severe hail the primary hazard
   accompanying the strong multicells/marginal supercells.  It is
   possible a portion of this region may require a probability upgrade
   in later outlooks if confidence increases for a concentrated area of
   storms/wind damage potential.

   ...Northern Great Plains...
   Upper forcing for ascent is expected to gradually overspread the
   region late in the day and overnight as a mid-level shortwave trough
   approaches the region.  Strong heating and steep lapse rates will
   yield 1000-2000 J/kg MLCAPE by late afternoon.  Models generally
   indicate only isolated thunderstorm coverage.  The stronger storms
   will potentially be capable of severe gusts/large hail beginning
   during the early evening and perhaps persisting on an isolated basis
   into the overnight.

   ..Smith/Lyons.. 07/12/2020

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