Sep 18, 2012 1630 UTC Day 1 Convective Outlook
Updated: Tue Sep 18 16:27:31 UTC 2012
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20120918 1630 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20120918 1630 UTC Day 1 Tornado Probabilities 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
20120918 1630 UTC Day 1 Damaging Wind Probabilities 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
20120918 1630 UTC Day 1 Large Hail Probabilities 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 181624
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1124 AM CDT TUE SEP 18 2012
   
   VALID 181630Z - 191200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS FROM NORTH CAROLINA NORTHWARD
   ACROSS VIRGINIA...THE WEST VIRGINIA EASTERN PANHANDLE
   ...MARYLAND...DELAWARE...EASTERN PENNSYLVANIA...WESTERN NEW JERSEY
   AND THE SOUTHERN-TIER OF NEW YORK...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA
   FROM SC TO SRN NEW ENGLAND...
   
   ...SYNOPSIS...
   A STRONG AND PROGRESSIVE UPPER TROUGH MORE CHARACTERISTIC OF AUTUMN
   THAN LATE SUMMER WILL SWING EAST/NORTHEAST FROM THE GREAT LAKES TO
   THE ST. LAWRENCE VALLEY WHILE AN ASSOCIATED SFC COLD FRONT SURGES
   EAST ACROSS THE APPALACHIANS AND INTO CNTRL NY/PA AND WRN VA BY LATE
   AFTERNOON...AND THEN CONTINUES INTO WRN NEW ENGLAND...AND ACROSS THE
   REMAINDER OF THE MID ATLANTIC REGION THROUGH LATE TONIGHT.
   ADDITIONALLY...A COMPACT BUT POTENT MID/UPPER LEVEL DISTURBANCE
   EMANATING FROM THE GULF COAST REGION AND ACCOMPANIED BY A 50-60KT
   MID LEVEL JET WILL RACE NORTH-NORTHEAST FROM AL/GA TO THE CAROLINAS
   THROUGH LATE AFTERNOON BEFORE BECOMING ABSORBED ALONG THE ERN FLANK
   OF THE LARGER DYNAMIC TROUGH FROM THE MID-ATLANTIC NORTHWARD.
   
   ...SOUTHEAST TO DELMARVA...
   FORECAST ACROSS THIS REGION IS COMPLICATED BY THE LEADING IMPULSE
   OVER SRN AREAS AND LIMITED INSTABILITY WITH NORTHWARD EXTENT.
   NONETHELESS...STRONG AND EXTENSIVE FLOW FIELDS CHARACTERIZED BY
   50-60 MID LEVEL SWLY FLOW ATOP LOW LEVEL SLY TO SSWLY FLOW AT
   30-60KT WERE ALREADY CONTRIBUTING TO MORE THAN ADEQUATE DEEP-LAYER
   SHEAR FOR LINEAR AND PERSISTENT STORM STRUCTURES AND STORM MOTIONS
   OF 40-50KT. BROAD REGION OF EFFECTIVE SRH VALUES OF 300-700 M2/S2
   ALSO EXISTS COINCIDENT WITH THE ANTECEDENT WARM/MOIST SECTOR WHERE
   LIFT WILL BE FOCUSED ALONG SEVERAL CONFLUENCE BANDS AHEAD OF THE
   LEADING IMPULSE EJECTING FROM AL/GA. ONGOING CONVECTION FROM SC/NC
   ACROSS SERN VA SHOULD SHOW A GRADUAL INCREASE IN VIGOR AS WEAK
   INSTABILITY RISES SLOWLY AND DYNAMIC FORCING STRENGTHENS THROUGH THE
   AFTERNOON. IN ADDITION TO A DAMAGING WIND THREAT FROM FAST-MOVING
   LINEAR SEGMENTS OF CONVECTION...CELLS NEAR LINE BREAKS...AND ANY
   DISCRETE STORMS...WILL EXIST IN AN ENVIRONMENT CONDUCIVE FOR STRONG
   LOW LEVEL ROTATION AND TORNADO POTENTIAL.
   
   ...DELMARVA TO ERN NY/WRN NEW ENGLAND....
   LOW-CAPE/HIGH-SHEAR AND STRONG DYNAMIC FORCING WITH THE UPPER TROUGH
   AND ADVANCING FRONT WILL DRIVE SEVERE STORM POTENTIAL ACROSS THESE
   AREAS FROM THE MID-ATLANTIC NORTH TO NEW ENGLAND...POTENTIALLY
   THROUGH LATE THIS EVENING. LOW LEVEL MOISTURE SURGE AND INTENSE WARM
   ADVECTION ACROSS THESE AREAS WERE CONTRIBUTING TO EXTENSIVE MOSTLY
   STRATIFORM RAIN AREA FROM NRN VA ACROSS NY/VT ATTM. THIS
   PRECIPITATION WILL SIGNIFICANTLY LIMIT DESTABILIZATION FOR THE TIME
   BEING DESPITE HIGH VALUES OF SHEAR/HELICITY. DESPITE THE LACK OF
   STRONGER INSTABILITY...KINEMATIC AND THERMODYNAMIC ENVIRONMENT WAS
   ALREADY SUPPORTING EMBEDDED LOW-TOPPED LINEAR CONVECTIVE STRUCTURES
   FROM NRN VA AND MD NWD TO SRN TIER OF NY. MAGNITUDE OF DEEP-LAYER
   FORCING FOR ASCENT JUST AHEAD OF THE ADVANCING COLD FRONT LATER THIS
   AFTERNOON COULD SUPPORT THE EVOLUTION OF A CORRIDOR WHERE MOIST
   ABSOLUTELY UNSTABLE LAYERS...IN THE PRESENCE OF INTENSE
   FLOW/SHEAR...RESULT IN THE DEVELOPMENT OF A FAST-MOVING NARROW COLD
   FRONTAL RAIN BAND/QLCS. STRENGTH OF LOW LEVEL MOISTURE AND MASS FLUX
   INTO AND AHEAD OF THIS BAND OF LOW-TOPPED CONVECTION SHOULD BE
   SUFFICIENT FOR DAMAGING WINDS ASSOCIATED WITH BOTH RAPID STORM
   MOTIONS AND PRECIPITATION LOADING WITHIN THE SQUALL LINE. A COUPLE
   OF BRIEF...BUT POTENTIALLY DAMAGING...TORNADOES CANNOT BE RULED OUT.
   
   THE MDT RISK AREA DEPICTS THE GREATEST POTENTIAL FOR THE ABOVE
   SCENARIO TO UNFOLD BETWEEN 19Z-00Z/2PM-8PM EDT.
   
   ..CARBIN/COHEN.. 09/18/2012
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z