SPC AC 101958

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0258 PM CDT Sat Apr 10 2021

   Valid 102000Z - 111200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR FAR SOUTHEAST
   GEORGIA AND PORTIONS OF THE NORTHERN AND WESTERN FLORIDA
   PENINSULA....

   ...SUMMARY...
   Isolated damaging gusts and a tornado or two will be possible this
   afternoon with a squall line across north Florida and south Georgia,
   as well as farther north across the Carolinas into the Ohio Valley.

   ...20Z Update...
   Expanded the marginal risk into central Lower Michigan. A broken
   line of storms has had an increase in lightning and shows some
   enhanced inbound velocities from the KGRR WSR-88D. The environment
   ahead of this activity is well mixed with temperatures in the low
   70s and dewpoints in the low 50s. Therefore, these storms may
   persist with the potential for an isolated damaging wind gust or
   two. Farther north, cloud cover has limited surface heating and
   therefore, this activity is expected to weaken by later this
   afternoon/early evening. 

   Otherwise, a slight uptick in storm intensity has occurred near the
   Georgia/Florida border within the last 1 to 2 hours. Continued
   destabilization ahead of this activity should be sufficient for
   these storms to continue for the next few hours before leaving the
   coast and entering the Atlantic. 

   The latest HRRR guidance continues to show strong storm development
   over the Gulf of Mexico late in the period. Some of these storms may
   reach coastal regions of southeast Louisiana through the Florida
   Panhandle, but the majority of this activity is expected to remain
   offshore through 12Z.

   ..Bentley/Gleason.. 04/10/2021

   .PREV DISCUSSION... /ISSUED 1126 AM CDT Sat Apr 10 2021/

   ...North FL/south GA this afternoon...
   A large MCS and associated cold pool, emanating from overnight
   convection, is moving eastward across the eastern FL Panhandle and
   southwest GA as of midday.  Lightning flash rates and echo tops have
   been diminishing some since late morning, which appears to be a
   reflection of the storms encountering lesser low-level moisture with
   eastward extent.  Some surface heating and modest moisture increases
   could maintain some threat for damaging winds into this afternoon
   across north FL/south GA, but the overall trend should be slowly
   downward through this evening.

   ...OH Valley through this evening...
   An occluded low over the middle MS Valley will move slowly
   northeastward toward IN by tonight.  Clouds are widespread in the
   warm sector of the system (north of the widespread convection along
   the Gulf coast), and midlevel lapse rates are relatively poor. 
   Pockets of surface heating in cloud breaks (mainly centered on OH)
   will support steepening low-level lapse rates and the potential for
   isolated strong gusts with pre-frontal convection this afternoon. 
   Farther west and closer to the surface cyclone/cold front, somewhat
   richer low-level moisture, but cooler surface temperatures, will
   tend to limit buoyancy this afternoon.  While low-level and
   deep-layer shear will be sufficient for some threat for low-topped
   supercells, the poor thermodynamic environment suggests that any
   tornado threat should remain rather limited.

   ...Carolinas/VA this afternoon into early tonight...
   A series of convectively-enhanced shortwave troughs will rotate
   northeastward from the southern Appalachians vicinity to the
   Carolinas/VA this afternoon into early tonight.  These embedded
   speed maxima will provide some forcing for ascent and a boost to
   low-level flow/shear, but they will also be accompanied by
   substantial cloud cover that will spread northeastward through the
   afternoon.  Thus, phasing of buoyancy (likely skewed closer to the
   coastal plain with richer moisture and longer-duration surface
   heating) and the somewhat stronger vertical shear (farther west with
   the thicker clouds) will be rather poor, which suggests that only
   low damaging wind and tornado probabilities are appropriate.

   ...Northeast Gulf coast early Sunday...
   In the wake of the widespread convection today, some increase in
   low-level warm advection and low-level recovery is expected
   overnight across the northeast Gulf of Mexico.  Destabilization
   could become sufficient for a marginal hail/wind threat, though the
   threat could be delayed until the end of the period as a result of
   the persistence and stabilizing influence of the ongoing convection.

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