SPC kicks risk up a notch
Posted by JAC on 6/9/2011, 2:57 pm


DAY 1 CONVECTIVE OUTLOOK  
  NWS STORM PREDICTION CENTER NORMAN OK
  1129 AM CDT THU JUN 09 2011
 
  VALID 091630Z - 101200Z
 
  ...THERE IS A MDT RISK OF SVR TSTMS ACROSS SOUTHERN
  VERMONT...SOUTHERN NEW HAMPSHIRE...MUCH OF
  MASSACHUSETTS...CONNECTICUT...SOUTHEAST NEW YORK...AND
  PENNSYLVANIA...
 
  ...THERE IS A SLGT RISK OF SVR TSTMS NEW ENGLAND WSWWD INTO THE
  CENTRAL PLAINS...
 
  ...THERE IS A SLGT RISK OF SVR TSTMS ERN WY AND VICINITY...
 
  ...SYNOPSIS...
  SUPPRESSION OF THE S CENTRAL AND SERN U.S. UPPER RIDGE IS FORECAST
  TO CONTINUE TODAY...AS THE WRN U.S. TROUGH SHIFTS EWD AND AT THE
  SAME TIME AN ERN CANADA TROUGH MOVES EWD -- FORCING FALLING
  HEIGHTS/CYCLONIC FLOW TO SPREAD ACROSS THE NORTHEAST CONUS.
 
  AT THE SURFACE...COLD FRONT WILL CONTINUE CROSSING THE ST. LAWRENCE
  VALLEY/LOWER GREAT LAKES REGION THIS MORNING...AND WILL BECOME A
  FOCUS FOR WIDESPREAD SEVERE STORM DEVELOPMENT AS IT SHIFTS INTO NEW
  ENGLAND/NY/PA.  THE OUTFLOW-REINFORCED FRONT WILL LINGER WWD ACROSS
  THE OH VALLEY...AND WILL RETREAT NWD WITH TIME ACROSS THE MO VALLEY
  REGION WITH FRONTAL LOW DEVELOPMENT EXPECTED IN THIS AREA IN
  RESPONSE TO EJECTING PIECES OF THE WRN U.S. TROUGH.
 
  ...NEW ENGLAND WSWWD ACROSS THE MIDWEST/OH VALLEY...
  POTENTIALLY WIDESPREAD/DAMAGING WIND EVENT IS FORECAST ACROSS THE
  NORTHEAST U.S. TODAY.  ONGOING CONVECTION ACROSS THIS RISK AREA HAS
  DIMINISHED EARLY THIS MORNING...WITH CONVECTIVE-COOLED AIR OVER SRN
  NEW ENGLAND EXPECTED TO CONTINUE RECOVERING.  AS A LARGE PLUME OF
  VERY STEEP LAPSE RATES ATOP A VERY MOIST /NEAR 70 DEWPOINTS/
  BOUNDARY LAYER COMBINES WITH CLEARING SKIES SUPPORTING STRONG WARM
  SECTOR HEATING...MIXED-LAYER CAPE OF 2000 TO 3000 J/KG IS EXPECTED
  TO DEVELOP QUICKLY THROUGH EARLY AFTERNOON.  AN OUTFLOW BOUNDARY
  INVOF THE MID AND UPPER OH VALLEY -- AND THE COLD FRONT NOW CROSSING
  THE LOWER GREAT LAKES/ST. LAWRENCE VALLEY -- WILL BECOME THE FOCUS
  FOR WIDESPREAD STORM DEVELOPMENT OVER THE NEXT COUPLE OF
  HOURS...SHIFTING SEWD WITH TIME ACROSS NY/PA/OH AND MUCH OF NEW
  ENGLAND.
 
  WITH STRONGEST DEEP-LAYER WLYS PROGGED TO REMAIN N OF THE
  MASON/DIXON LINE...MOST WIDESPREAD SEVERE THREAT APPEARS TO EXIST
  FROM SWRN PA ENEWD ACROSS SRN AND ERN NY INTO SRN NEW ENGLAND.
  HERE...VERY LARGE HAIL THREAT WITH INITIAL SUPERCELL STORMS SHOULD
  EVOLVE INTO MORE OF A DAMAGING WIND THREAT AS CONVECTION EVOLVES
  INTO ONE OR MORE BOWING LINES WHICH WILL MOVE QUICKLY EWD.  A COUPLE
  OF TORNADOES MAY ALSO OCCUR -- PARTICULARLY EARLY ON WITH MORE
  ISOLATED STORMS.
 
  BY THIS EVENING...CONVECTION WILL HAVE SHIFTED WELL SEWD...FROM SRN
  AND ERN NEW ENGLAND WSWWD INTO NRN VA/WV.  WITH WEAKER FLOW S OF THE
  MASON/DIXON LINE...MORE ISOLATED SEVERE POTENTIAL IS FORECAST.  
 
  ...MID MO VALLEY REGION AND VICINITY SWWD INTO NRN OK...
  COMPLEX SCENARIO EXISTS ACROSS THE CENTRAL PLAINS/MID MO VALLEY
  REGION...AS EARLY MORNING SHORT-WAVE RIDGING ALOFT IS FORECAST TO
  CONTINUE WEAKENING AS TROUGHING SHIFTS ENEWD.  AS SURFACE LOW
  REDEVELOPS NWD INTO THE MID MO VALLEY REGION IN RESPONSE TO THE
  APPROACHING TROUGH...AND THE SURFACE FRONT OVER NRN MO RETREATS NWD
  INTO IA...STORM DEVELOPMENT WILL OCCUR -- SUPPORTED BY MODERATE TO
  STRONG WARM SECTOR DESTABILIZATION.  
 
  WITH BACKING/STRENGTHENING LOW-LEVEL FLOW INVOF THE DEVELOPING
  LOW/WARM FRONT BENEATH 50 KT SWLYS AT MID LEVELS SPREADING ATOP THIS
  AREA...SHEAR/INSTABILITY COMBINATION WILL BE QUITE SUPPORTIVE OF
  SUPERCELLS.  ALONG WITH THREAT FOR VERY LARGE HAIL...ISOLATED
  TORNADOES WILL ALSO BE POSSIBLE -- MAINLY FROM SERN NEB/NERN KS EWD
  INTO NRN MO/SRN IA.  LOCALLY DAMAGING WINDS WILL ALSO BE
  POSSIBLE...POSSIBLY BECOMING MORE LIKELY WITH TIME AS SOME
  CLUSTERING OF CONVECTION OCCURS INTO THE EVENING HOURS.
 
  MORE ISOLATED STORM DEVELOPMENT IS FORECAST TO OCCUR SWD ACROSS
  CENTRAL/ERN KS AND INTO OK...NEAR AND AHEAD OF THE SURFACE COLD
  FRONT.  ALONG WITH POTENTIAL FOR HAIL...DEEP/DRY SUB-CLOUD MIXED
  LAYER WILL SUPPORT EVAPORATIVELY-ENHANCED DOWNDRAFTS -- AND THUS
  SOME LIKELIHOOD FOR LOCALLY DAMAGING GUSTS.
 
  ...ERN WY AND VICINITY...
  DESPITE FAIRLY EXTENSIVE MORNING CLOUD COVER...SOME DESTABILIZATION
  WILL SUPPORT AFTERNOON STORM DEVELOPMENT -- INITIALLY OVER THE
  HIGHER TERRAIN BUT THEN SPREADING EWD INTO LOWER ELEVATIONS.  WITH
  STRONG /50 TO 60 KT/ MID-LEVEL WLY JET STREAK SHIFTING ACROSS THIS
  REGION...SHEAR WILL SUPPORT ORGANIZED/SUPERCELL STORMS...AND THUS --
  DESPITE POSSIBLY LIMITED INSTABILITY IN PARTS OF THE AREA --
  CONTINUATION OF SLIGHT RISK FOR HAIL IS WARRANTED.  MORE ISOLATED
  THREAT APPEARS TO EXTEND SWD INTO THE CO FRONT RANGE AREA...AS
  SUBSIDENCE EVIDENT IN THE WAKE OF A SEPARATE/DEPARTING SHORT-WAVE
  TROUGH SHOULD LIMIT COVERAGE A BIT WITH SWD EXTENT.
 
  ..GOSS/SMITH.. 06/09/2011
 
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Squall Line could hit NYC around Rush Hour - JAC, 6/9/2011, 2:53 pm
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