SWODY1
SPC AC 080555
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 AM CDT SAT SEP 08 2007
VALID 081200Z - 091200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF SERN NY AND SRN
NEW ENGLAND...
..SYNOPSIS...
MAIN BELT OF POLAR WESTERLIES WILL EXTEND FROM WRN CANADA ACROSS THE
NRN BORDER STATES FROM THE INTERIOR NORTHWEST...NRN PLAINS/GREAT
LAKES...TO NRN NEW ENGLAND BEFORE ARCING CYCLONICALLY BACK INTO ERN
CANADA. A POTENT LEADING IMPULSE THAT EJECTED ACROSS THE GREAT LAKES
REGION ON FRIDAY WILL MOVE RAPIDLY ACROSS ERN CANADA TODAY WITH A
DEEP CYCLONE MOVING OFF THE COAST OF LABRADOR TONIGHT. COLD FRONT
ASSOCIATED WITH THIS SYSTEM WILL MOVE EAST FROM THE ERN GREAT LAKES
AND ACROSS NRN NEW ENGLAND THROUGH LATE TODAY. EXTENSIVE TRAILING
SEGMENT OF THIS BOUNDARY...FROM OH SWWD TO THE SRN PLAINS...WILL
BECOME STALLED AND ALIGNED WITHIN WEAK WSWLY MEAN LAYER FLOW ON THE
NRN FRINGE OF SUBTROPICAL RIDGE AXIS.
NEXT UPSTREAM SHORT WAVE TROUGH WILL TRACK FROM THE DAKOTAS TO MN
THROUGH TONIGHT WITH ASSOCIATED COLD FRONT SURGING SWD ACROSS THE
CNTRL PLAINS. WITH DEEP MOISTURE FOCUSED ALONG THE STALLED BOUNDARY
ACROSS THE MIDWEST/SRN PLAINS...THIS SECONDARY FRONTAL SURGE WILL
ENCOUNTER SOMEWHAT LIMITED MOISTURE AS IT SPREADS SWD ACROSS THE
CNTRL PLAINS LATER TODAY.
..FRONTAL ZONE FROM TX/OK TO NEW ENGLAND...
POCKETS OF STRONG HEATING /TEMPERATURES IN THE 80S-90S F/ COUPLED
WITH ABUNDANT LOW LEVEL MOISTURE /DEWPOINTS IN THE 70S F/ WILL
RESULT IN AREAS OF WEAKLY CAPPED MODEST DESTABILIZATION ALONG AND
AHEAD OF EXTENSIVE FRONTAL ZONE FROM THE PLAINS TO THE NORTHEAST.
LARGE SCALE FLOW AND FORCING ALONG THIS EXTENSIVE CORRIDOR WILL BE
QUITE WEAK AS STRONGER HEIGHT FALLS SPREAD INTO CANADA.
ONE REGION WITH A SLIGHTLY HIGHER PROBABILITY FOR SEVERE STORMS MAY
EVOLVE FROM SERN NY ACROSS PARTS OF SRN ENGLAND DURING THE
AFTERNOON. AN AXIS OF STRONGER INSTABILITY /MLCAPE PERHAPS TO 2000 J
PER KG/ IS FORECAST TO DEVELOP AHEAD OF DIFFERENTIAL HEATING ZONE
FROM SERN NY ACROSS MA DURING THE AFTERNOON. SCATTERED CONVECTION
SHOULD ERUPT WITHIN THIS ZONE THROUGH THE AFTERNOON AS WEAK
CONVECTIVE INHIBITION IS OVERCOME BY STRONG HEATING/RECORD HIGH
TEMPERATURES. GIVEN GENERALLY WEAK SHEAR BUT DEEP-LAYER WLY FLOW
AROUND 20KT...EXPECT A FEW MULTICELLULAR STORM CLUSTERS SPREADING
EAST WITH DAMAGING WINDS AND PERHAPS SOME HAIL.
FARTHER SOUTH AND WEST...VARIOUS SMALLER SCALE PERTURBATIONS
EMBEDDED WITHIN THE WEAK MID LEVEL FLOW WILL RESULT IN AREAS OF
ENHANCED ASCENT/SURFACE DEVELOPMENT ALONG THE STALLED FRONT. A FEW
BETTER-ORGANIZED STORM CLUSTERS MAY EVOLVE THROUGH LATE
AFTERNOON/EARLY EVENING COINCIDENT WITH STRONGER INSTABILITY AND
MESOSCALE FORCING. ISOLATED TO WIDELY SCATTERED WIND/HAIL EVENTS
APPEAR POSSIBLE WITH THIS CONVECTION. HOWEVER...GIVEN WEAK SHEAR AND
POORLY RESOLVED MESOSCALE FEATURES PROMOTING GREATER SEVERE STORM
POTENTIAL...ONLY LOW SEVERE PROBABILITIES ARE BEING FORECAST OVER A
LARGE AREA ALONG THE FRONTAL ZONE.
..CNTRL HIGH PLAINS...
STRONG HEATING/STEEPENING LOW LEVEL LAPSE RATES AND MARGINAL
MOISTURE WILL CONTRIBUTE TO WEAK/MODEST DESTABILIZATION AHEAD OF THE
FRONT SURGING SWD ACROSS THE HIGH PLAINS. LIFT ALONG THE FRONT
SHOULD BE SUFFICIENT FOR ISOLATED TSTM DEVELOPMENT DURING THE LATE
AFTERNOON AND EARLY EVENING. FORECAST SOUNDINGS INDICATE FAVORABLE
PARAMETERS FOR LOCALLY STRONG DOWNDRAFTS AND PERHAPS SOME HAIL FROM
HIGH-BASED CONVECTION FORMING ALONG AND IN THE WAKE OF THE SURFACE
FRONT. LIMITED INSTABILITY AND STORM COVERAGE PRECLUDES HIGHER
SEVERE PROBABILITIES ACROSS THIS REGION.
..ERN DAKOTAS/WRN MN...
FOCUSED AREA OF STRONGLY FORCED ASCENT AND POTENT LOW LEVEL SHEAR
WILL ACCOMPANY COMPACT SURFACE LOW TRACKING EWD FROM THE ERN DAKOTAS
TO WRN MN LATE IN THE DAY. WHILE AIR MASS IS FORECAST TO BE ONLY
MARGINALLY UNSTABLE WITH MLCAPE OF 200-300 J PER KG... MAGNITUDE OF
LOW LEVEL FORCING COUPLED WITH DIURNAL MAX IN AVAILABLE INSTABILITY
MAY BE SUFFICIENT FOR A COUPLE OF STRONGER STORM UPDRAFTS. NARROW
WINDOW OF GREATER TORNADO POTENTIAL COULD EVOLVE AROUND 21-00Z GIVEN
EFFECTIVE SURFACE-BASED SRH ON THE ORDER 300 M2/S2. UNCERTAINTIES
REGARDING TIMING AND INSTABILITY PRECLUDE A HIGHER RISK AT THIS
TIME.
.CARBIN/JEWELL.. 09/08/2007
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