DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 221247
SWODY1
SPC AC 221245

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0745 AM CDT SAT SEP 22 2012

VALID 221300Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID ATLANTIC NORTH TO
ERN NY AND WRN NEW ENGLAND...

...SYNOPSIS...
THE HIGHLY AMPLIFIED UPPER AIR PATTERN IN PLACE ACROSS THE CONUS
TODAY WILL BE COMPRISED OF A RIDGE AXIS OVER THE WEST AND
ROCKIES...A PACIFIC SHORT WAVE TROUGH MAKING INROADS ACROSS THE
NORTHWEST COAST...AND A LARGE AND COMPLEX MID/UPPER TROUGH OVER THE
GREAT LAKES. LIFT WITH THE TROUGH MOVING INLAND ACROSS THE NORTHWEST
SHOULD PROMOTE SCATTERED SHOWERS AND A FEW TSTMS FROM THE CASCADES
ESEWD TO THE NRN GREAT BASIN. HOWEVER...DEEP-LAYER WIND FIELDS OVER
THESE AREAS WILL REMAIN GENERALLY WEAK AND NON-SUPPORTIVE OF MORE
ORGANIZED STORMS.

CONSIDERABLY STRONGER DEEP-LAYER FLOW EXISTS WITHIN THE BASE OF THE
LARGE SCALE TROUGH FROM THE UPPER MS VALLEY TO THE ERN GREAT LAKES.
WITHIN A BELT OF PRONOUNCED CYCLONIC FLOW ACROSS THESES
AREAS...500MB WIND SPEEDS WERE APPROACHING 100KT AND MORNING WATER
VAPOR IMAGERY DEPICTED SEVERAL SHORT WAVE IMPULSES/VORT MAXIMA
MOVING THROUGH THE LARGER SCALE SYSTEM. AT LEAST TWO OF THESE
DISTURBANCES WILL DRIVE TSTM POTENTIAL FROM THE LOWER GREAT LAKES
INTO PARTS OF THE NORTHEAST AND MID-ATLANTIC TODAY.

...MID ATLANTIC TO NY/WRN NEW ENGLAND...
A LEADING SHORT WAVE IMPULSE ASSOCIATED WITH FRIDAY/S SEVERE TSTMS
OVER THE MIDWEST HAS ROTATED THROUGH THE BASE OF THE LARGER SCALE
TROUGH AND WAS MOVING RAPIDLY NNEWD INTO QB THIS MORNING. SUBSIDENCE
IN THE WAKE OF THIS DEPARTING DISTURBANCE WILL INITIALLY LIMIT
ASCENT ALONG THE TRAILING COLD FRONT FROM WRN NY/PA TO THE OH
VALLEY. THE BREAK IN STRONGER DPVA AND ENHANCED ASCENT ALONG THE
COLD FRONT WILL BE SHORT LIVED. THE NEXT STRONG SHORT WAVE
DISTURBANCE WILL SWING THROUGH THE BASE OF THE GREAT LAKES
TROUGH...FROM LM TO OH...THROUGH THE AFTERNOON. AS THIS
OCCURS...RENEWED FORCING FOR ASCENT WILL ACT TO STRENGTHEN/SHARPEN
THE FRONTAL ZONE...COINCIDENT WITH MAXIMUM IN DIURNAL.

LOW LEVEL MASS TRANSPORT ASSOCIATED WITH THE LEADING SHORT WAVE
TROUGH NOW MOVING INTO QB HAS CONTRIBUTED TO THE DEVELOPMENT OF A
NARROW PLUME OF RICHER LOW LEVEL MOISTURE WITH 55 TO LOWER 60S F
DEWPOINTS AHEAD OF THE COLD FRONT FROM NY SWD TO VA. SUBSIDENCE
BEHIND THE LEADING IMPULSE SHOULD ALLOW FOR INSOLATION THROUGH THE
MORNING/EARLY AFTERNOON WITH SBCAPE RISING TO ABOUT 250-500 J/KG IN
NRN AREAS...AND REACHING AROUND 1000 J/KG IN THE SOUTH. PRE-FRONTAL
FORECAST SOUNDINGS DEPICT A RESIDUAL WARM LAYER ALOFT THAT MAY ACT
TO INHIBIT BUOYANCY AND PARCEL ACCELERATIONS...AT LEAST DURING
INITIAL CONVECTIVE DEVELOPMENT PHASE. HOWEVER...WITH TIME...A FORCED
BROKEN SQUALL LINE OF LOW-TOPPED CONVECTION SHOULD EVOLVE AS THE
COLD FRONT STRENGTHENS AND SPREADS EAST FROM CNTRL NY/PA DURING THE
LATE AFTERNOON. WEAKER FORCING WITH SWD EXTENT INTO THE MID-ATLANTIC
REGION SUGGESTS THAT PROSPECTS FOR STORM DEVELOPMENT AND
ORGANIZATION MAY BE LESS IN THESE AREAS...DESPITE STRONGER
INSTABILITY.

AS THE CHANCE FOR LATE AFTERNOON/EARLY EVENING CONVECTION INCREASES
FROM DELMARVA NORTH TO NY/VT...MID LEVEL WINDS AND RESULTING SHEAR
WILL STRENGTHEN CONSIDERABLY TO SUPPORT FAST-MOVING LINE
SEGMENTS/LEWPS CAPABLE OF DAMAGING WINDS...AND PERHAPS EVEN A
BRIEF/ISOLATED TORNADO. IN THE NORTH...ACTIVITY WILL WEAKEN RAPIDLY
WITHIN AN HOUR OR TWO AFTER SUNSET WHILE FARTHER SOUTH...STORMS
SHOULD MOVE OFF MOST OF THE EAST COAST...SOUTH TO DELMARVA...BEFORE
MIDNIGHT.

...LOWER MI ACROSS OH/WRN PA...
DESPITE A COOLER POST-FRONTAL AIRMASS AND WEAK LOW LEVEL
CONVERGENCE...POCKETS OF STRONGER SURFACE HEATING AND PROXIMITY OF
WARMER LAKE WATERS...COULD LEND SUPPORT TO A CLUSTER OF MORE
VIGOROUS STORMS AS LIFT WITH THE COMPACT VORT MAX SPREADS ESEWD
ACROSS THESE AREAS FROM LATE MORNING INTO EARLY AFTERNOON. LACK OF
GREATER DESTABILIZATION SHOULD TEMPER A MORE SIGNIFICANT HAIL THREAT
BUT A FEW CELLS COULD STILL PRODUCE MARGINAL HAIL AND GUSTY WINDS.

..CARBIN/BOTHWELL.. 09/22/2012

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@LISTSERV.ILLINOIS.EDU with
"unsub wx-storm" in the body of your message. For more information write cnovy@cox.net.