SPC AC 231630

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1130 AM CDT Sun Apr 23 2017

   Valid 231630Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER
   WESTERN/CENTRAL GEORGIA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTH
   CAROLINA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTHERN
   FLORIDA INTO GEORGIA AND SOUTH CAROLINA...

   ...SUMMARY...
   Areas of strong-severe thunderstorms are expected over the Southeast
   today and overnight.  The main threats appear to be damaging gusts
   over parts of western/central Georgia and central South Carolina
   this afternoon, followed by potential for a few tornadoes and
   isolated wind damage overnight in parts of South Carolina.

   ...Georgia and South Carolina...
   Satellite imagery indicates an upper low has formed over western
   Tennessee, and this feature is forecast to move southeastward
   reaching the Alabama/Georgia border by the end of the period.  A
   band of stronger mid/upper level winds curving cyclonically around
   the southern periphery of the circulation is expected to spread
   across parts of Georgia and northern Florida into tonight.

   At the surface, a low over extreme northwest Georgia will move
   mainly eastward along a quasi-stationary front extending across
   east-central Georgia to the central South Carolina coast.  The low
   is forecast to reach east-central Georgia this evening and cross
   into South Carolina by 24/12Z. A cold front trailing southward from
   the low will progress eastward to the Atlantic coast from Georgia to
   northeast Florida by the end of the period.  The frontal boundaries
   are expected to focus the stronger thunderstorm activity through
   tonight.

   Initial storm development is expected along the advancing cold front
   by early afternoon from west central Georgia into the Florida
   Panhandle as it moves into an axis of slightly greater moisture. 
   Although mid-level lapse rates are generally weak, visible satellite
   imagery indicates stronger diabatic heating will occur in the warm
   sector where fewer clouds are present.  This will enhance low-level
   lapse rates and contribute to modest destabilization with MLCAPE of
   500-1000 J/kg this afternoon.  With some CAM guidance indicating
   development of QLCS structures along/slightly ahead of the front,
   stronger cells within the line segments will have potential to
   produce damaging downbursts as they move through the focused
   moisture/instability axis.  See Mesoscale Discussion 550 for more
   detailed information.

   Other storms are expected to develop over parts of central/southern
   South Carolina this afternoon near the aforementioned east-west
   front.  The lack of clouds south of the boundary is promoting a
   strong differential heating zone where attendant mesoscale
   circulations will support storm potential this afternoon. Isolated
   severe storms will be possible as vertical shear increases over the
   area, especially along and immediately north of the boundary where
   backed surface flow will enhance low-level shear.

   The severe threat over South Carolina is expected to increase
   somewhat tonight as a south-southeasterly low-level jet strengthens
   in response to the approaching upper low.  This will result in
   increasing moisture advection from the Atlantic and be associated
   with stronger low-level shear with an attendant risk for supercells
   to develop.  Low LCL levels and moderate-strong SRH indicate
   potential for a few tornadoes to occur with any persistent discrete
   supercells that develop.

   ...Northern/Central Utah...
   Isolated weak thunderstorms may develop this afternoon and evening
   in association with an upper short wave trough that will move
   eastward across the Great Basin.  Column moisture/total precipitable
   water values are quite minimal /approximately 0.25 inch/ which will
   limit the coverage and intensity of any convection.  However, a dry
   sub-cloud layer will enhance evaporative cooling and promote
   transfer of stronger mid-level horizontal momentum to the surface,
   suggesting potential for convectively-enhanced surface wind gusts. 
   Given the aforementioned limiting factors, we will maintain a
   sub-severe outlook at this time over the area.

   ..Weiss/Cook.. 04/23/2017

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