SPC AC 231726

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1226 PM CDT Sun Apr 23 2017

   Valid 241200Z - 251200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS MONDAY ACROSS
   THE CAROLINA COASTAL PLAIN AND PARTS OF THE ADJACENT PIEDMONT...

   ...SUMMARY...
   Thunderstorms accompanied by at least some severe weather potential
   may impact the Carolina coastal plain and portions of the adjacent
   piedmont Monday.

   ...Synopsis...
   Models indicate that a strong belt of westerlies, traversing much of
   the mid-latitude Pacific into the interior western U.S., will
   undergo some amplification during this period.  As broad mid/upper
   ridging builds across the eastern Pacific through the U.S. Pacific
   coast, broad downstream troughing appears likely to evolve near the
   nose of the stronger flow, across the Great Basin and Rockies.  In
   lower levels, an initial surface cyclone, developing to the lee of
   the Rockies in association with this regime, appears likely to
   migrate northeast of the Black Hills region and weaken during the
   day Monday, with new surface cyclogenesis taking place near/north of
   the Texas/Oklahoma Panhandle region late Monday through Monday
   night.

   Meanwhile, within split westerlies downstream of the Rockies, broad
   ridging within the northern stream is expected to build across and
   northeast of the Great Lakes region.  Within the southern stream,
   troughing over the Southeast may gradually pivot from a neutral to
   negative tilt while progressing east of the Atlantic coast.  As it
   does, a modest embedded lower/mid tropospheric cyclone is forecast
   to redevelop from near or just south of the southern Appalachians
   into areas near or east of the Carolina coast by 12Z Tuesday. 
   Appreciable spread is evident among the various models, and within
   their respective ensemble output, concerning these developments and
   possible interaction/consolidation with an impulse within the
   subtropical westerlies (now progressing across/northeast of southern
   Florida and the Bahamas).

   ...South Atlantic Coast...
   It remains unclear what, if any, impact that the model spread
   concerning the evolution of the synoptic system will have on the
   forecast for this period.  Even though it appears that the highest
   moisture content air (characterized by 70F+ surface dew points) will
   generally remain confined to areas well offshore, a substantive
   influx of moisture still seems likely across/inland of the Carolina
   coast.  This is expected to contribute to sufficient destabilization
   for considerable convective development.  The extent to which
   mid-level cooling is able to steepen lower/mid tropospheric lapse
   rates remains uncertain, and it is not clear that there will be
   sufficient breaks in the overcast across inland areas to allow for
   appreciable surface heating.  Deep layer mean wind fields and shear
   within the warm sector of the low may not be much more than 30 kt. 
   However, it may not be out of the question that the environment
   could become conducive to thunderstorms with at least some severe
   weather potential, mainly across parts of the South Carolina
   piedmont into coastal plain during the day Monday, and perhaps the
   North Carolina coastal plain Monday night.

   ...Nrn intermountain region/Rockies into north central Plains...
   Steepening of lapse rates associated with mid-level cooling, and the
   northeastward advection of elevated mixed layer air to the lee of
   the southern Rockies, may contribute to sufficient destabilization
   for at least widely scattered thunderstorm activity, in the presence
   of favorable orographic and synoptic forcing for ascent.  This
   probably will be accompanied by at least some potential for hail in
   stronger cells, including activity based within lower/mid
   tropospheric warm advection across parts of the north central Plains
   Monday into Monday night.  However, destabilization, in general,
   will be substantially inhibited across the Plains by the lack of a
   substantive return flow of moisture off the Gulf of Mexico, in the
   wake of the Southeastern system.  And pockets of potentially
   substantive destabilization across the Rockies and intermountain
   region remain too uncertain (and likely to remain rather sparse) to
   allow a forecast of 5 percent severe probabilities at this time.

   ..Kerr.. 04/23/2017

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