DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 220530
SWODY1
SPC AC 220528

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 AM CDT SAT SEP 22 2012

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MIDDLE ATLANTIC INTO
PORTIONS OF UPSTATE NY...

...ERN U.S...

EARLY MORNING WV IMAGERY DEPICTS AT LEAST TWO WELL DEFINED UPPER
VORT MAXIMA WITHIN THE BROADER GREAT LAKES TROUGH. THE LEAD VORT
APPEARS TO BE PARTLY RESPONSIBLE FOR ONGOING CONVECTION ACROSS THE
OH VALLEY AND SHOULD DRIVE AN ASSOCIATED SFC LOW NEWD INTO SERN
ONTARIO/QUEBEC EARLY IN THE PERIOD. AS THE SFC LOW TRANSLATES
ACROSS THE UPPER OH VALLEY INTO SERN ONTARIO THE TRAILING COLD FRONT
SHOULD SWEEP EWD INTO WRN NY/PA BY SUNRISE. SUBSEQUENT MOVEMENT
SHOULD PLACE THE BOUNDARY ALONG ERN SHORE OF LAKE ONTARIO...SWD INTO
CNTRL PA BY 18Z.

LOW LEVEL MOISTURE IS NOT PARTICULARLY ABUNDANT AHEAD OF THE COLD
FRONT ACROSS THE MIDDLE ATLANTIC WITH SFC DEW POINTS ONLY IN THE
UPPER 50S/LOWER 60S BUT TRAJECTORIES FAVOR A GRADUAL MOISTENING NWD
INTO ERN NY AS LLJ STRENGTHENS NORTH OF THE BORDER NEAR THE SFC LOW.
LATEST FORECAST SOUNDINGS SUGGEST FRONTAL CONVECTION SHOULD DEVELOP
ACROSS NY/PA DURING THE 18-21Z TIME FRAME AS TEMPERATURES WARM
THROUGH THE MID 60S OVER NY AND INTO THE 70S OVER PA. EVEN SO
BUOYANCY IS NOT EXPECTED TO BE THAT GREAT AS MARGINAL LAPSE RATES
SHOULD CONTRIBUTE TO SBCAPE VALUES ON THE ORDER OF 500-1000 J/KG
FROM NORTH TO SOUTH ALONG THE FRONT. AT THIS TIME IT APPEARS STRONG
DEEP LAYER SHEAR WILL ENHANCE THE LIKELIHOOD FOR LINEAR TSTM
DEVELOPMENT ALONG THE ADVANCING BOUNDARY AND SHORT BOWING SEGMENTS
COULD EVOLVE ALONG SQUALL LINE AS IT ADVANCES INTO THE HUDSON
VALLEY...SWD INTO DE BY 23/00Z. GIVEN THE LIMITED THERMODYNAMIC
ENVIRONMENT STRONG/DAMAGING WINDS SHOULD BE THE PRIMARY SEVERE
THREAT AND TSTM INTENSITY SHOULD BE MAXIMIZED DURING THE 18-00Z TIME
FRAME.

...ERN ME...

DOWNSTREAM ACROSS NRN NEW ENGLAND...WV IMAGERY SUGGESTS A WEAK
DISTURBANCE AND DEEPER MOISTURE PLUME WILL GLANCE PORTIONS OF ME AND
NB. IF SFC DEW POINTS RISE INTO THE LOWER 60S AS LATEST NAM
GUIDANCE SUGGESTS SFC BASED CONVECTION/ISOLATED THUNDERSTORMS COULD
EVOLVE WITHIN THE WARM CONVEYOR. SHEAR PROFILES WOULD SUPPORT
ROTATING UPDRAFTS AND A FEW WEAK SUPERCELLS COULD DEVELOP. IT/S NOT
ENTIRELY CLEAR HOW MUCH TSTM ACTIVITY WILL DEVELOP ALONG THE WRN
FRINGE OF THIS PLUME BEFORE IT IS SHUNTED DOWNSTREAM ACROSS NB. FOR
THIS REASON HAVE OPTED TO INTRODUCE 2 PERCENT SEVERE PROB FOR
TORNADOES AND 5 PERCENT FOR LOCALLY DAMAGING WINDS. GREATEST THREAT
FOR ROBUST UPDRAFTS WITHIN MOIST/MARGINALLY UNSTABLE AIRMASS WILL BE
PRIOR TO 21Z.

..DARROW/GARNER.. 09/22/2012

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