SPC AC 041724

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1224 PM CDT Thu Nov 04 2021

   Valid 051200Z - 061200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON
   INTO FRIDAY NIGHT ACROSS THE CENTRAL AND SOUTHERN FLORIDA
   PENINSULA...

   ...SUMMARY...
   Strong thunderstorms may impact the central and southern Florida
   Peninsula Friday and perhaps Friday night.  Some of these may pose
   potential to produce a couple of tornadoes, in additional to a risk
   for locally damaging wind gusts.

   ...Synopsis...
   Large-scale mid-level troughing appears likely to continue to
   progress across the eastern Pacific, toward the Pacific coast, with
   downstream ridging forecast to build across much of the Rockies and
   Great Plains.  To the east of the ridging, models indicate that a
   more prominent split in the flow will continue to evolve Friday
   through Friday night.  While flow trends more zonal across the Upper
   Midwest through the Northeast, a modestly amplified trough in the
   developing southern branch of mid-latitude westerlies is forecast to
   progress across the Southeast and northeastern Gulf of Mexico,
   toward the southern Atlantic coast.  This troughing is coming
   increasingly in phase with a belt of westerlies emanating from the
   subtropical Pacific, and expected to remain so through this period,
   with large-scale forcing for ascent appearing likely to support the
   onset of cyclogenesis along a stalling frontal zone across the
   southeastern Gulf of Mexico through the central Florida Peninsula.

   ...Florida...
   The details of the frontal wave development through this period
   differ substantively among the various model output, but guidance,
   in general, suggests that deepening of the surface low across the
   eastern Gulf of Mexico through the Florida Peninsula will remain
   rather modest to weak into at least early Saturday.  This may limit
   strengthening of lower/mid-tropospheric wind fields on a broader
   scale, and probably is the primary consideration precluding higher
   severe probabilities at the present time.

   Lower/mid-tropospheric lapse rates are likely to remain weak and
   early day cloud cover/precipitation may inhibit or slow inland
   development of the warm sector, but it appears that this will
   include seasonably moist air returning from the southeastern Gulf of
   Mexico and Caribbean.  In the presence of strengthening deep-layer
   shear, mixed-layer CAPE increasing in excess of 500 J/kg will at
   least become marginally supportive of organized strong thunderstorm
   development.

   Of possible increasing note, the 12Z NAM suggests that there may be
   a mesoscale area of modest strengthening southerly 850 mb flow
   during the afternoon, in a corridor roughly from Fort Myers through
   the Vero Beach vicinity.  This is at least similarly depicted in the
   04/00Z ECMWF, and forecast soundings indicate that this may be
   accompanied by at least modestly enlarging, clockwise-curved
   low-level hodographs beneath moderate to strong southwesterly flow
   in the 500-300 mb layer.  Profiles near the low-level speed maximum
   appear to become conducive to discrete supercell development with
   the potential to produce tornadoes as it progresses across the
   peninsula from mid to late afternoon.  While there is not yet much
   of a signal concerning this in the latest HREF ensemble, this will
   need to be monitored and it is still possible that severe weather
   probabilities could be increased in later outlooks for this period.

   ..Kerr.. 11/04/2021

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