SPC AC 092000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT THU JUN 09 2011
VALID 092000Z - 101200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF
PA/NY/NJ/NH/CT/RI/MA/VT...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SOUTHERN
PLAINS/MIDWEST TO NEW ENGLAND...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS EASTERN WY/FAR NORTHEAST
CO...

...NORTHEAST STATES/NEW ENGLAND...
BANDS OF INTENSE THUNDERSTORMS CONTINUE TO MERGE/EXPAND AND GROW
UPSCALE THIS AFTERNOON WITH A BROAD/WELL-ORGANIZED LINE OF TSTMS NOW
EVOLVING ACROSS THE NORTHEAST STATES/SOUTHERN NEW ENGLAND. SPECIAL
16Z/18Z OBSERVED SOUNDINGS REFLECT VERY STRONG INSTABILITY/STEEP
LAPSE RATES ON THE SOUTHERN FRINGE OF STRONG WESTERLIES ALOFT.
SCENARIO STILL EXPECTED TO YIELD WIDESPREAD WIND DAMAGE IN ADDITION
TO BOUTS OF LARGE HAIL AND PERHAPS A BRIEF TORNADO OR TWO. GIVEN
AMPLE PRE-CONVECTIVE LINE HEATING/SOUTHWESTERLY FLOW...THE PRIMARY
20Z CHANGE WAS TO EXTEND THE MODERATE RISK EASTWARD ACROSS VIRTUALLY
ALL OF THE SOUTHERN NEW ENGLAND COAST. PLEASE REFERENCE
ONGOING/SUBSEQUENT WATCHES AND MESOSCALE DISCUSSIONS.

...LOWER/MIDDLE MO VALLEY AND MIDWEST/SOUTH-CENTRAL PLAINS...
PRIOR REASONING GENERALLY HOLDS...ALTHOUGH INTRODUCED SOMEWHAT
HIGHER TORNADO PROBABILITIES /10 PERCENT/ IN GENERAL VICINITY OF AN
OUTFLOW-AIDED TRIPLE POINT ACROSS THE LOWER-MIDDLE MO VALLEY.
REFERENCE MESOSCALE DISCUSSION 1155.
ANOTHER CHANGE WAS TO EXTEND THE SLIGHT RISK SOUTHWESTWARD IN
VICINITY OF THE DRYLINE ACROSS FAR SOUTHWEST OK INTO PORTIONS OF THE
EASTERN TX PANHANDLE/NORTHWEST TX. HERE...DAMAGING WINDS/SOME HAIL
MAY BE A CONCERN LATE THIS AFTERNOON/EARLY EVENING.
..GUYER.. 06/09/2011
.PREV DISCUSSION... /ISSUED 1129 AM CDT THU JUN 09 2011/

...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.