Categorical Graphic
Probabilistic Tornado Graphic
Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.

   SPC AC 281258
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0758 AM CDT THU APR 28 2011
   
   VALID 281300Z - 291200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS TODAY ALONG THE ATLANTIC
   COAST...
   
   ...SYNOPSIS...
   A DEEP-LAYER CYCLONE AND ASSOCIATED TROUGH COVERING MUCH OF THE ERN
   CONUS IS ASSOCIATED WITH A SFC COLD FRONT EXTENDING NORTH-TO-SOUTH
   FROM THE GREAT LAKES ACROSS THE MIDDLE ATLANTIC AND FARTHER S INTO
   THE FL PANHANDLE AND NERN GMEX. AS THE INTENSE DEEP-LAYER FLOW EAST
   OF THE TROUGH AXIS BECOMES ORIENTED MORE PARALLEL TO THE FRONT...AND
   AN THE ATTENDANT SFC CYCLONE OCCLUDES OVER SRN ONTARIO/QUEBEC...THE
   FRONT IS FORECAST TO DECELERATE ITS EWD PROGRESS BEFORE IT NEARS THE
   ATLANTIC COASTLINE...EVENTUALLY MOVING OFFSHORE TONIGHT. A PLUME OF
   DEEP-LAYER MOISTURE /PWAT VALUES OF 1.50 TO 1.80 INCHES/ EXTENDS
   FROM THE NERN GULF NNEWD TO MAINE IN ASSOCIATION WITH A
   MERIDIONALLY-EXPANSIVE MOIST SECTOR...WHICH WILL GRADUALLY SHIFT EWD
   WHILE PRECEDING THE FRONT.
   
   ...ATLANTIC SEABOARD...
   ONGOING CONVECTION LEADING THE FRONT EXTENDS FROM VT TO ERN PA SSWWD
   TO THE FL PANHANDLE...AND WILL CONTINUE SHIFTING EWD TOWARD THE
   ATLANTIC COAST THIS MORNING. WITH AN INTENSE PREFRONTAL LOW-LEVEL
   JET /55 KT AT 1 KM AGL SAMPLED BY STERLING VA VWP/ AND REGIONAL
   RADARS DEPICTING A PRIMARILY LINEAR CONVECTIVE MODE...DMGG WINDS
   WILL REMAIN A PROMINENT THREAT. HOWEVER...EFFECTIVE SRH VALUES AOA
   300 M2/S2 WILL MAINTAIN THE THREAT FOR A FEW TORNADOES WITH ANY
   QLCS-EMBEDDED MESOVORTICES. THIS IS ESPECIALLY THE CASE WITH MORE
   ROBUST CONVECTION DEEPER INTO THE WARM SECTOR ACROSS ERN PORTIONS OF
   VA...THE CAROLINAS...AND GA...WHERE SFC DEWPOINTS RANGE FROM THE
   MIDDLE 60S TO LOWER 70S.
   
   BY LATE MORNING AND EARLY AFTERNOON...THE BULK OF THE CURRENT
   CONVECTION OVER THE SERN STATES AND THE CAROLINAS IS EXPECTED TO
   HAVE SHIFTED OFF THE MIDDLE ATLANTIC COAST...WHILE ACTIVITY FARTHER
   NORTH LEAVES THE STRONGER INSTABILITY AND WEAKENS OVER THE STABLE
   MARINE LAYER ENTRENCHED OVER ERN NEW ENGLAND. MEANWHILE...THE DRY
   CONVEYOR BELT WRAPPING AROUND THE DEEP-LAYER CYCLONE WILL PROVIDE A
   TEMPORARILY LULL IN THE CONVECTION EARLY THIS AFTERNOON...ALONG WITH
   AN OPPORTUNITY FOR A BREAKS IN THE DEBRIS CLOUDS TO MATERIALIZE.
   WITH DIURNAL HEATING IN THE MOIST SECTOR...MLCAPE VALUES AOA 1000
   J/KG ARE FORECAST TO DEVELOP ACROSS SERN VA AND POINTS SOUTH...WITH
   MORE MARGINAL INSTABILITY FARTHER NORTH. PREFRONTAL CONFLUENCE BANDS
   AND FRONTAL CONVERGENCE WILL PROVIDE THE IMPETUS FOR INITIATING
   BANDS OF CONVECTION ALONG AND EAST OF THE FRONT BY EARLY AFTERNOON.
   
   FORECAST SOUNDINGS INDICATE SFC WINDS GRADUALLY VEERING WITH TIME AS
   THE FRONT APPROACHES...YIELDING LONG...STRAIGHT-LINE HODOGRAPHS
   GIVEN 0-6-KM BULK SHEAR MAGNITUDES AOA 45 KT. THUS...THE PRIMARY
   CONVECTIVE MODE IS EXPECTED TO BE BROKEN LINE SEGMENTS...WITH DMGG
   WINDS THE MAIN SVR CONCERN. HOWEVER...A FEW TORNADOES WILL ALSO BE
   POSSIBLE...ESPECIALLY GIVEN THE STRENGTH OF LOW-LEVEL VERTICAL
   SHEAR. ACROSS ERN NC AND SERN VA...SFC WINDS MAY REMAIN BACKED FOR A
   SOMEWHAT LONGER DURATION GIVEN THE ORIENTATION OF THE COASTLINE AND
   FAVORABLE MOISTURE TRAJECTORIES FROM A WRN ATLANTIC SUBTROPICAL
   MOISTURE PLUME. AS SUCH...DISCRETE STORMS /SOME SUPERCELLULAR/ HAVE
   A HIGHER POTENTIAL OF DEVELOPING IN THIS REGION...POSING AN ENHANCED
   THREAT FOR DMGG WINDS AND TORNADOES. STEEP MID-LEVEL LAPSE RATES
   COULD ALSO YIELD SOME INSTANCES OF LARGE HAIL...ESPECIALLY OVER THE
   MIDDLE ATLANTIC AND SOUTHEAST STATES IN CLOSER PROXIMITY TO RICHER
   LOW-LEVEL MOISTURE. THE SVR THREAT IS FORECAST TO HAVE SHIFTED OFF
   THE ATLANTIC COAST BY LATE EVENING.
   
   ...LOWER OHIO VALLEY...
   COLD MID-LEVEL TEMPERATURES IN ASSOCIATION WITH A VORT MAX PIVOTING
   AROUND THE PRIMARY CYCLONE WILL SUPPORT THE DEVELOPMENT OF STEEP
   LOW/MID-LEVEL LAPSE RATES IN RESPONSE TO SFC HEATING BENEATH THE
   COLD CORE /500-MB TEMPS OF -22C TO -24C/. A REINFORCING COLD FRONT
   DROPPING SOUTH OUT OF THE LOWER GREAT LAKES REGION WILL FOCUS THE
   DEVELOPMENT OF BANDS OF LOW-TOPPED CONVECTION MOVING S/SEWD FROM
   MID-AFTERNOON THROUGH THE EARLY EVENING. GIVEN THE COLD TEMPS
   ALOFT...A FEW INSTANCES OF LARGE HAIL COULD OCCUR. DMGG WINDS CANNOT
   BE RULED OUT GIVEN LOW-LEVEL LAPSE RATES APPROACHING DRY ADIABATIC
   IN SOME AREAS AND THE PRESENCE OF STRONGER MOMENTUM ALOFT.
   
   ..THOMPSON/COHEN.. 04/28/2011
   
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