angelwing, you are in the Moderate Risk area so be careful there.
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT TUE SEP 18 2012
VALID 182000Z - 191200Z
...THERE IS A MDT RISK OF SVR TSTMS FROM THE MID ATLANTIC REGION
INTO THE NERN STATES...
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN VA THROUGH ERN
MD...DEL AND NJ...
...MID ATLANTIC INTO THE NERN STATES...
FORCED PRE-FRONTAL SQUALL LINE AND A FEW DISCRETE STORMS CONTINUE
THROUGH THE MID ATLANTIC AND NERN STATES. PRIMARY LIMITING FACTOR SO
FAR HAS BEEN THE VERY MARGINAL THERMODYNAMIC
ENVIRONMENT...ESPECIALLY WITH NWD EXTENT INTO THE NERN U.S. WHERE
SFC LAYER DEWPOINTS ARE SOMEWHAT LOWER AND RAIN HAS BEEN MORE
WIDESPREAD. VERY LARGE HODOGRAPHS AND STRONG DEEP SHEAR WILL PERSIST
OVER THIS REGION INTO THE EVENING AS STRENGTHENING 60+ KT LLJ LIFTS
THROUGH THE REMAINDER OF THE MID ATLANTIC AND NEW ENGLAND IN
ASSOCIATION WITH A NEWD EJECTING NRN STREAM SHORTWAVE TROUGH.
DESPITE THE LIMITING EFFECTS OF WEAK INSTABILITY...WILL MAINTAIN A
SMALL MDT RISK UNTIL THE 01Z UPDATE FROM ERN VA INTO ERN MD...DEL
AND NJ WHERE WIND DAMAGE COULD BE MORE CONCENTRATED AHEAD OF THE
MORE ORGANIZED AND MORE INTENSE PORTION OF THE SQUALL LINE THAT
STILL CONTAINS BOWING AND LEWP STRUCTURES.
..DIAL.. 09/18/2012
.PREV DISCUSSION... /ISSUED 1124 AM CDT TUE SEP 18 2012/
...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.
