SPC AC 161939
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0239 PM CDT SAT MAY 16 2009
VALID 162000Z - 171200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF LOWER GREAT
LAKES INTO MID ATLANTIC STATES...
...LOWER GREAT LAKES/HUDSON VALLEY SWD INTO THE CNTRL APPALACHIANS
THROUGH THIS EVENING...
MULTIPLE BANDS AND/OR CLUSTERS OF TSTMS ARE ONGOING THIS AFTERNOON
IN ADVANCE OF SURFACE COLD FRONT WHICH EXTENDED FROM THE VICINITY OF
LAKES ONTARIO AND ERIE SWWD INTO WRN PARTS OF KY/TN AS OF 19Z.
WHILE MIDLEVEL LAPSE RATES REMAIN WEAK...STRONGER INSOLATION FROM
THE ALLEGHENY RANGE SWD/SEWD ALONG THE BLUE RIDGE AND PIEDMONT OF VA
IS CONTRIBUTING TO AN AXIS OF STRONGER INSTABILITY WITH MLCAPE
RANGING FROM 500-1000 J/KG OVER N-CNTRL PA TO AS HIGH AS 1000-1500
J/KG OVER CNTRL VA.
WATER VAPOR IMAGERY AND LATEST SHORT TERM MODEL DATA INDICATE THE
PRESENCE OF EMBEDDED WEAKER IMPULSES PRECEDING PRIMARY UPPER SYSTEM
OVER THE UPPER GREAT LAKES. FORCING FOR ASCENT ASSOCIATED WITH
THESE FEATURES COUPLED WITH THE DESTABILIZING AIR MASS SHOULD
CONTINUE TO MAINTAIN STRONG TO SEVERE TSTMS INTO THIS EVENING. THE
STRONGEST LOW AND DEEP-LAYER SHEAR WILL REMAIN ACROSS NY/PA PORTION
OF SLIGHT RISK WHERE TRAILING EXTENSION OF 30-40 KT LLJ IS
COINCIDENT WITH 40-50 KT WSWLY MIDLEVEL FLOW. HERE...POTENTIAL WILL
EXIST FOR EMBEDDED SUPERCELL/BOWING STRUCTURES CAPABLE OF DAMAGING
WINDS...SOME HAIL AND PERHAPS A BRIEF TORNADO OR TWO. VERTICAL
SHEAR DECREASES FAIRLY RAPIDLY WITH SWD EXTENT...BUT THE STRONGER
INSTABILITY SHOULD SERVE TO MAINTAIN A DAMAGING WIND AND ISOLATED
HAIL THREAT INTO THIS EVENING.
THE OVERALL SEVERE WEATHER THREAT SHOULD BEGIN TO DIMINISH BY
MID/LATE EVENING AS PRE-FRONTAL BOUNDARY LAYER BEGINS TO
COOL/STABILIZE.
..MEAD.. 05/16/2009
.PREV DISCUSSION... /ISSUED 1121 AM CDT SAT MAY 16 2009/
...ERN KY/WV INTO NY/PA AND PARTS OF THE NRN MID ATLANTIC...
COMPLEX FORECAST ACROSS THIS REGION AHEAD OF DEEP UPPER TROUGH AND
STRONG MID/UPPER LEVEL JETS SHIFTING ACROSS THE GREAT LAKES AND
ONTARIO/WRN QUEBEC TODAY. SURFACE COLD FRONT IS EXPECTED TO OUTRUN
MOST INTENSE FLOW ALOFT...ALTHOUGH MODEST WSWLY MID/UPPER LEVEL
WINDS WILL CONTINUE ACROSS THE WARM SECTOR FROM PORTIONS OF THE
CENTRAL APPALACHIANS INTO THE NORTHEAST THROUGH THIS EVENING.
SURFACE PATTERN IS ILL-DEFINED ACROSS ERN NY/PA LATE THIS MORNING
WITH PERSISTENT LOW CLOUDS EXTENDING FROM THE DELMARVA NWD INTO ERN
NY...WHILE MODEST HEATING IS ALLOWING SOME MIXING AND SWLY SURFACE
WINDS TO DEVELOP OVER WRN PA/NY AHEAD OF MAIN COLD FRONT EXTENDING
FROM ONTARIO INTO WRN OH AND SRN IN AT 16Z.
SEVERE THREAT MAY INCREASE INTO THE EARLY AFTERNOON WITH LEADING
LINE/AREA OF TSTMS GRADUALLY STRENGTHENING OVER SWRN NY THROUGH THE
LATE MORNING. HOWEVER... OVERALL THREAT OF ISOLATED DAMAGING WIND
AND HAIL IS EXPECTED TO INCREASE ALONG SURFACE COLD FRONT LATER THIS
AFTERNOON FROM PORTIONS OF KY INTO WRN PA/NY. REFERENCE SWOMCD 845.
ACTIVITY SHOULD DEVELOP AS SMALL LINES WITH PRIMARY THREAT OF
DAMAGING WINDS FROM PORTIONS OF KY NEWD INTO THE EVENING.
ALTHOUGH...STRONG LOW LEVEL SHEAR WOULD SUPPORT AN ADDITIONAL RISK
OF A TORNADO OR TWO INTO PORTIONS OF NY/PA WITH ANY PERSISTENT
SUPERCELL. SEVERE THREAT SHOULD DIMINISH THIS EVENING INTO ERN NY
AND THE NRN MID ATLANTIC AS INSTABILITY WANES.
...S TX...
RESIDUAL...SLOW MOVING VORT CENTER OVER CENTRAL TX WILL LIKELY
CONTINUE TO FOCUS SCATTERED TSTMS AHEAD OF SURFACE COLD FRONT GIVEN
VERY MOIST/UNSTABLE WARM SECTOR. ACTIVITY WILL BE SLOW MOVING
WITHIN WEAK FLOW REGIME AND SUPPORT VERY HEAVY RAINFALL
RATES...ALONG WITH ISOLATED DOWNBURST/HAIL NEAR SEVERE LEVELS INTO
THE EVENING.
...SRN APPALACHIANS...
WEAK SRN STREAM IMPULSE APPEARS TO BE SHIFTING ACROSS AL/WRN GA THIS
MORNING WHICH WILL LIKELY FOCUS AN AREA OF STRONGER...SHORT-LIVED
TSTMS THIS AFTERNOON ACROSS THIS AREA. SHEAR AND MID LEVEL LAPSE
RATES REMAIN WEAK...ALTHOUGH SHORT-LIVED SEVERE TSTMS CAN BE
EXPECTED TODAY.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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