SPC AC 210729

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0229 AM CDT Thu Mar 21 2024

   Valid 231200Z - 241200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS EARLY SATURDAY
   ACROSS PARTS OF SOUTHERN FLORIDA AND PARTS OF COASTAL NORTH
   CAROLINA...

   ...SUMMARY...
   Strong thunderstorms posing at least some risk for severe weather
   may approach or perhaps spread inland across the Outer Banks
   vicinity of North Carolina early Saturday, as the risk for strong to
   severe thunderstorm development diminishes across parts of southern
   Florida.

   ...Synopsis...
   As a more progressive regime continues to spread across the central
   into eastern mid-latitude Pacific, blocking initially centered over
   the northeastern Pacific is forecast to gradually begin to
   breakdown.  As this occurs, models suggest that downstream flow may
   undergo amplification across the southern mid- and subtropical
   latitudes, inland of the Pacific coast into the western Atlantic. 
   It appears that this will include large-scale mid-level troughing
   digging across the Pacific coast through the Southwest, with at
   least a couple of significant embedded short wave perturbations. 
   This will be preceded by building ridging across the Great Plains
   into Mississippi Valley, and digging mid-level troughing offshore of
   the southern Atlantic Seaboard.  

   In higher latitudes, a vigorous short wave impulse turning eastward
   across the Great Lakes by 12Z Saturday (to the south of an
   elongating circulation across southern Hudson Bay into northern
   Manitoba) is forecast to accelerate east-northeastward through much
   of the St. Lawrence Valley by early Sunday, trailed by a
   perturbation emerging from the troughing to the south.  Initially
   accelerating northeastward to the lee of the southern Appalachians
   at the outset of the period, there appears increasing consensus that
   this trailing impulse may support a compact deepening surface low,
   within elongating surface troughing mostly offshore of the Atlantic
   coast.  However, there is considerable lingering spread concerning
   this and other sub-synoptic developments across and east of the
   Atlantic Seaboard.

   In the wake of the developing surface low, a significant ongoing
   cold intrusion to the lee of the Rockies is forecast to overtake the
   offshore surface troughing late Saturday through Saturday night. 
   Models indicate that the southwestern flank of this cold air will
   stall and begin to undergo modification across the lower Mississippi
   Valley into central high plains, as surface troughing begins to
   deepen to the lee of the Front Range and southern Rockies.

   ...Florida...
   It is possible that an outflow boundary may linger across parts of
   the southern peninsula and/or Florida Keys into Saturday morning,
   with potential for continuing vigorous thunderstorm development
   accompanied by at least some risk for strong, gusty winds.  It
   appears that this boundary will shift off to the east and south by
   midday, if not earlier.

   In its wake, models indicate low-level flow quickly veering to an
   increasingly westerly component across the remainder of the
   peninsula, leading to diminishing convective potential ahead of a
   weak approaching cold front.

   ...Eastern North Carolina...
   Severe weather potential appears largely conditional, depending on
   the evolution and track of the primary surface low.  However, the
   inland advection of a moist unstable warm sector appears at least
   possible early Saturday, within a strongly sheared environment
   across the Outer and Inner Banks vicinity.  This may provide a
   window of opportunity for organized convective development,
   including supercells.

   ..Kerr.. 03/21/2024

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