SPC AC 152000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0200 PM CST Mon Feb 15 2021

   Valid 152000Z - 161200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS INTO THIS
   EVENING FROM THE FL PANHANDLE INTO SOUTHWEST GA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVERNIGHT ACROSS
   PORTIONS OF THE COASTAL CAROLINAS...

   ...SUMMARY...
   Scattered damaging winds and a few tornadoes are likely across the
   Florida Panhandle into south Georgia through early evening. A strong
   tornado or two is possible. Severe thunderstorms are also possible
   across north Florida and overnight into the coastal Carolinas.

   ...FL Panhandle into southern GA...
   The primary change with this outlook is to trim severe probabilities
   and the general thunderstorm line in the wake of the convective band
   running from south AL into the FL Panhandle and the northern Gulf of
   Mexico. Otherwise, the previous forecast rationale remains valid.
   With boundary-layer dewpoints increasing into the mid-upper 60s
   dewpoints across the FL Panhandle and a very favorable wind profile
   in place, supercells capable of producing tornadoes, strong wind
   gusts, and isolated hail remain possible into the late
   afternoon/early evening, with the threat eventually spreading into
   southwest GA by early evening. See MCD 90 and the previous outlook
   discussion below for more information. 

   ...North Florida...
   Scattered thunderstorms have developed across north FL this
   afternoon, in the vicinity of a surface boundary. A couple of
   supercells may eventually evolve in this area, posting a threat of
   all severe hazards. See MCD 92 for more information. 

   ...Coastal Carolinas...
   A separate area of strong/locally severe thunderstorm development is
   still expected across portions of the coastal Carolinas late
   tonight. See the previous discussion below for more information.

   ..Dean.. 02/15/2021

   .PREV DISCUSSION... /ISSUED 1030 AM CST Mon Feb 15 2021/

   ...FL Panhandle to south GA...
   Upgraded to cat 3/ENH risk for the potential of a strong tornado or
   two along with scattered damaging winds likely, a few of which may
   be significant.

   Scattered thunderstorms are underway from the surface cyclone that
   is near the far southeast tip of LA into the north-central Gulf
   along a sharp cold front. Additional convection may also develop
   within the next couple hours ahead of this activity within
   pre-frontal bands of confluence evident in visible satellite
   imagery. As the surface cyclone deepens towards the AL/GA/FL border
   area, the warm front should advance inland across the FL Panhandle
   reaching southern GA by early evening. Mid to upper 60s F surface
   dew points are expected in that regime, supporting a pronounced
   gradient of MLCAPE from north to south, approaching 1500 J/kg along
   the coast. Expect strengthening mid/upper winds supporting 50-65-kt
   southwesterly effective-shear vectors, oriented just slightly
   rightward of the main corridor of convective forcing with an
   elongated mid/upper-level portion of the hodograph. The southern
   fringe of a 45-60-kt LLJ will contribute to low-level hodograph
   curvature with 200-400 m2/s2 effective SRH, greatest along the warm
   front.

   Pervasive stratus north of the warm front renders uncertainty over
   the degree of tornado coverage as near-surface lapse rates may
   remain less than ideal. However, the preceding favorable factors may
   compensate and a conditional risk for a strong tornado or two is
   apparent this afternoon. The tornado threat should subside some this
   evening as the primary surface cyclone occludes across the western
   portion of the Appalachians with the shortwave trough progressing
   rapidly northeast away from the region.

   ...Coastal Carolinas...
   Elevated thunderstorms should spread northeastward over interior
   areas tonight, as a northward extension of the Gulf regime. A
   separate, prefrontal low-level convergence zone is forecast to
   support increasing thunderstorms tonight and affect coastal areas
   through the end of the period.  A damaging-gust threat may develop
   very near the coastline, where boundary-layer instability may be at
   least marginally favorable, with tornado potential from any mature
   supercell that can cross the coast. Farther northwestward, isolated
   strong-severe gusts may penetrate the near-surface stable layer,
   with potential diminishing with inland extent.

   Along the coast, buoyancy will increase with proximity to the Gulf
   Stream, where vertical heat/moisture fluxes will provide the most
   sustained air mass modification. Forecast soundings still indicate
   shallow near-surface stable layers at the bottom of the lifted layer
   yielding surface- based effective-inflow parcels. However, vertical
   shear will be favorable, with 45-55-kt effective-shear magnitudes
   and effective SRH around 200-300 J/kg.

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