Re: Early Fall Storm to Bring Heavy Rains to the Appalachians
Posted by hanna on 9/18/2012, 1:01 pm
I've been watching all Gulf Coast & East Coast on radar.  My area had rain since early today; thunder was bad earlier but has been off in the distance we are out of the severe thunder storm box.  Other areas are not so lucky.
I don't know how this is.




Severe Thunderstorms Possible From Mid-Atlantic to New England
The NWS Storm Prediction Center is forecasting a risk of severe thunderstorms Tuesday afternoon and evening form northern South Carolina across the Mid-Atlantic and into southern New England. The main threat is widespread damaging wind, though a few tornadoes are possible, as well. In addition, moderate to heavy rain is possible over parts of the Northeast.


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
  CURRENT UTC TIME: 1630Z (12:30PM), RELOAD THIS PAGE TO UPDATE THE TIME


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Early Fall Storm to Bring Heavy Rains to the Appalachians - hanna, 9/17/2012, 10:34 am
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