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 280609
   
   DAY 1 CONVECTIVE OUTLOOK CORR 1
   NWS STORM PREDICTION CENTER NORMAN OK
   0109 AM CDT THU APR 28 2011
   
   VALID 281200Z - 291200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ALONG THE ATLANTIC SEABOARD...
   
   CORRECTED FOR NDFD GRIDS
   
   ...SYNOPSIS...
   AS A PARENT UPPER LOW ELONGATES OVER THE MIDWEST-CNTRL GREAT LAKES
   TODAY...STRONG IMPULSE CURRENTLY OVER THE TN VLY WILL EJECT NE TO
   NEW ENGLAND.  A COLD FRONT WILL SURGE EWD ACROSS THE NERN STATES AS
   A DEEP SFC CYCLONE TRAVELS FROM IND TO QUEBEC.  TRAILING FRONT WILL
   BE SLOWER TO MOVE ACROSS THE MID-SRN ATLANTIC COASTAL AREAS.
   
   ...ATLANTIC SEABOARD...
   STRONG SLY LOW-LEVEL FLOW WILL MAINTAIN A VERY MOIST AIR MASS
   ALONG/AHEAD OF AN APPROACHING BAND OF STRONG-SEVERE TSTMS TODAY. 
   ALTHOUGH MID-LEVEL LAPSE RATES WILL DECREASE WITH NRN
   EXTENT...MLCAPES WILL STILL LIKELY REACH 1000 J/KG GIVEN INFLUX OF
   RICH LOW-LEVEL MOISTURE.  FARTHER S...STEEPER LAPSE RATES AND
   EXPECTED WARMER TEMPERATURES WILL RESULT IN A COMPARATIVELY MORE
   UNSTABLE AIR MASS FROM PARTS OF SERN PA SWD INTO NRN FL.  
   
   DEEP-LAYER FLOW BEGINS TO BECOME MORE ALIGNED WITH TIME AS THE
   MID-LEVEL WAVE EJECTS ENE AND WITH INCREASING ASCENT...ACTIVITY FROM
   THE NRN MID-ATLANTIC NWD INTO NY SHOULD BECOME MORE QUASI-LINEAR
   WITH EMBEDDED ROTATING STRUCTURES.  DMGG WINDS AND ISOLATED
   TORNADOES WILL BE POSSIBLE THERE.  ACTIVITY WILL WEAKEN WITH EWD
   EXTENT AS IT ENCOUNTERS THE MARINE LAYER FLOWING OFF THE NEW ENGLAND
   COASTAL ATLANTIC.  
   
   FARTHER S...CORE OF THE STRONGEST LOW-LEVEL JET IS EXPECTED TO
   TRANSLATE NWD EARLY IN THE DAY...BUT FORECAST SOUNDINGS SUGGEST THAT
   AMPLE DEEP/LOW-LEVEL SHEAR WILL LINGER THROUGH EARLY AFTERNOON FROM
   CNTRL MID-ATLANTIC STATES SWD INTO THE CAROLINAS.  HERE...DISCRETE
   SUPERCELLS WITH A FEW TORNADOES AND DMGG WINDS WILL EXIST.  THESE
   THREATS WILL MOVE BEYOND THE COAST BY MID-LATE AFTERNOON. 
   
   TAIL-END OF THE COLD FRONT WILL BECOME INCREASINGLY REMOVED FROM
   STRONGER DEEP LAYER SHEAR WITH TIME ACROSS THE SERN ATLANTIC
   SEABOARD.  BUT...REMNANT PRE-FRONTAL OUTFLOW
   BOUNDARY MAY ENHANCE LOW-LEVEL CONVERGENCE ALONG THE ATLANTIC COAST
   SEA BREEZE...IN THE PRESENCE OF LARGE CAPE DURING THE PEAK AFTERNOON
   HEATING.  DMGG WINDS/HAIL WILL BE THE PRIMARY SVR RISKS.
   
   ...LOWER OHIO VALLEY...
   MODELS INDICATE THAT A FAIRLY SIGNIFICANT SHORT WAVE
   IMPULSE/MID-LEVEL LOBE OF CYCLONIC VORTICITY WILL PIVOT
   EAST/SOUTHEASTWARD ACROSS THE REGION DURING THE DAY THURSDAY...TO
   THE SOUTH OF THE ELONGATING CLOSED LOW.  DURING PEAK AFTERNOON
   HEATING...ASSOCIATED LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION
   IS EXPECTED TO CONTRIBUTE TO CONVECTIVE DEVELOPMENT BENEATH THE
   MID-LEVEL COLD CORE OF THE UPPER TROUGH /500 MB TEMPS OF -22 TO
   -24C/. STEEP LAPSE RATES AND PRESENCE OF MODEST WLY LOW/MID-LEVEL
   FLOW WILL CONTRIBUTE TO FAST-MOVING STORMS WITH AN ISOLD DMGG
   WIND/HAIL THREAT.  ACTIVITY SHOULD LARGELY BE DIURNAL AND DIMINISH
   DURING THE EVE.
   
   ..RACY/DEAN.. 04/28/2011
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z