SPC MESOSCALE DISCUSSION 1336 FOR ERN NY/WRN MA/VT/NH/WRN ME
CONCERNING...SEVERE THUNDERSTORM POTENTIAL... 

VALID 011409Z - 011600Z 

NEW WW WILL BE NEEDED ACROSS AREA SHORTLY...WITH THREAT FOR DAMAGING
WINDS INCREASING THROUGH THE EARLY AFTERNOON HOURS. 

PRE-FRONTAL SQUALL LINE CONTINUES TO INCREASE IN AREAL COVERAGE AND
INTENSIFY OVER THE EASTERN GREAT LAKES REGION...AND IS BEGINNING TO
ACCELERATE EASTWARD TOWARD THE CHAMPLAIN/HUDSON VALLEYS AT AROUND 45 KT.
DAYTIME HEATING IS CONTRIBUTING TO RAPID DESTABILIZATION FROM THIS AREA
INTO MUCH OF NEW ENGLAND...WHICH WILL MAINTAIN ACTIVITY...SUPPORTED BY
STRONG FORCING FOR UPWARD VERTICAL MOTION AHEAD OF VIGOROUS SHORT WAVE
TROUGH SWEEPING INTO THE EASTERN GREAT LAKES REGION.  SWATH OF
STRONG/DAMAGING WIND GUSTS APPEARS LIKELY TO ACCOMPANY SQUALL LINE ALONG
AN AXIS FROM JUST NORTH OF ALBANY NY INTO THE PORTLAND ME AREA BY THE
18-19Z TIME FRAME. 

..KERR.. 07/01/01



SPC MESOSCALE DISCUSSION 1338 FOR WRN PA...MUCH OF OH...CNTRL IND
CONCERNING...SEVERE THUNDERSTORM POTENTIAL... 

VALID 011444Z - 011700Z 

CONVECTIVE TRENDS ACROSS THE OHIO VALLEY ARE BEING MONITORED.  ONE OR
MORE SEVERE THUNDERSTORM WATCHES MAY BE NEEDED WITHIN THE NEXT COUPLE OF
HOURS. 

PRE-FRONTAL SQUALL LINE IS INCREASING IN AREAL COVERAGE AND INTENSIFYING
ACROSS THE EASTERN GREAT LAKES AND OHIO VALLEY.  GIVEN WEAK CAP/RAPID
DESTABILIZATION ASSOCIATED WITH SURFACE HEATING/AND STRENGTHENING
LOW-LEVEL CONVERGENCE...THIS TREND IS LIKELY TO CONTINUE INTO THE EARLY
AFTERNOON HOURS FROM AREAS NORTH AND WEST OF PITTSBURGH PA...WESTWARD
TOWARD THE INDIANAPOLIS IND AREA. STEADY INCREASE IN STRENGTH OF MEAN
FLOW...ASSOCIATED WITH JET STREAK IN BASE OF SHORT WAVE TROUGH DIGGING
ACROSS THE GREAT LAKES REGION...WILL SUPPORT ACCELERATING SOUTHEASTWARD
STORM MOTION AND INCREASING THREAT FOR DAMAGING WINDS...PARTICULARLY
FROM EASTERN OHIO AND WESTERN PENNSYLVANIA SOUTHEASTWARD TOWARD THE
CENTRAL APPALACHIANS. 

IN RESPONSE TO HEIGHT RISES ACROSS THE UPPER MISSISSIPPI VALLEY... TAIL
END OF SQUALL LINE OVER PARTS OF CENTRAL INDIANA WILL BE SLOW
MOVING/QUASI-STATIONARY...BUT STRENGTHENING VERTICAL SHEAR PROFILES WILL
STILL SUPPORT AT LEAST A THREAT OF LARGE HAIL AFTER 18Z. 

..KERR.. 07/01/01



SPC MESOSCALE DISCUSSION 1340 FOR WRN/NRN NY STATE CONCERNING...SEVERE
THUNDERSTORM WATCH 485... 

VALID 011641Z - 011800Z 

ONGOING INTENSE LINE OF THUNDERSTORMS...NOW EXTENDING FROM AREAS
SOUTH/EAST OF WATERTOWN INTO AREAS EAST OF ROCHESTER...IS OCCURRING JUST
AHEAD OF COLD FRONT.  FRONT WILL BEGIN TO ACCELERATE EASTWARD ACROSS NEW
YORK STATE LATER THIS AFTERNOON...AS 995 MB SURFACE LOW OVER SOUTHEAST
QUEBEC CONTINUES TO DEEPEN AND LIFT NORTHEASTWARD. HOWEVER...THIS DOES
NOT APPEAR LIKELY TO OCCUR PRIOR TO 18Z...WHEN WW 485 IS SCHEDULED TO
EXPIRE.  THUS...NEW SHORT DURATION WW WILL LIKELY BE NEEDED FOR PARTS OF
CENTRAL NEW YORK STATE IMMEDIATELY UPSTREAM OF WW 486. 

..KERR.. 07/01/01



SPC MESOSCALE DISCUSSION 1341 FOR NJ/SE NY/CT/RI/SE MA/LONG ISLAND
CONCERNING...SEVERE THUNDERSTORM POTENTIAL... 

VALID 011756Z - 012000Z 

NEW WW WILL LIKELY BE NEEDED ACROSS AREA WITHIN NEXT HOUR OR SO. 
LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION ASSOCIATED WITH VIGOROUS
SHORT WAVE SWEEPING INTO THE EASTERN GREAT LAKES REGION CONTINUES TO
SUPPORT EVOLUTION OF EXTENSIVE PRE-FRONTAL SQUALL LINE FROM NORTHERN NEW
ENGLAND INTO THE OHIO VALLEY.  BETWEEN 18- 20Z...ACTIVITY WILL BEGIN TO
GRADUALLY SPREAD EAST SOUTHEASTWARD INTO NORTHERN MID ATLANTIC COASTAL
AREAS/THE LOWER HUDSON VALLEY/AND SOUTHERN NEW ENGLAND...WHERE AIR MASS
IS WARM/MOIST AND MODERATELY UNSTABLE.  BAND OF STRONGER 50+ KT
MID-LEVEL FLOW NOW OVER NORTHWESTERN PENNSYLVANIA AND UPSTATE NEW YORK
WILL GRADUALLY SPREAD TOWARD THE NORTHERN MID ATLANTIC/NEW ENGLAND COAST
BY THROUGH 02/00Z...ENHANCING STORM MOTION AND THREAT FOR DAMAGING WIND
GUSTS. 

..KERR.. 07/01/01



SPC MESOSCALE DISCUSSION 1342 FOR OH/PA/WV/NRN VA/NRN MD
CONCERNING...SEVERE THUNDERSTORM WATCH 487...488... 

VALID 011851Z - 012100Z 

NEW WWS MAY BE NEEDED SOUTH OF 487 AND 488 BY THE 21-22Z TIME FRAME. 

AT 18Z...STRONGER 2 HOUR SURFACE PRESSURE FALLS EXTENDED ALONG AN AXIS
AHEAD OF PRE-FRONTAL SQUALL LINE...FROM SOUTHEAST OHIO THROUGH NORTH
CENTRAL WEST VIRGINIA/CENTRAL MARYLAND/AND SOUTHEAST PENNSYLVANIA INTO
THE LOWER HUDSON VALLEY.  AIR MASS ALONG THIS AXIS IS WARM/MOIST AND
POTENTIALLY UNSTABLE WITH SURFACED-BASED CAPE ON THE ORDER OF 2000
J/KG...WHICH WILL MAINTAIN STRENGTH OF SQUALL LINE INTO THE EARLY
EVENING HOURS.  30 TO 50 KT MID-LEVEL FLOW ON SOUTHERN FRINGE OF THE
STRONGER WESTERLIES WILL CONTINUE TO SUPPORT SMALL BOWING SEGMENTS
EMBEDDED WITHIN SQUALL LINE... ACCOMPANIED BY ENHANCED RISK OF DAMAGING
WIND GUSTS. 

..KERR.. 07/01/01



SPC MESOSCALE DISCUSSION 1346 FOR SERN NH/NERN MA 
CONCERNING...SEVERE THUNDERSTORM WATCH 489... 

VALID 012138Z - 012300Z 

INDIVIDUAL CELLS IN SQUALL LINE MOVING ABOUT 265/40 KNOTS. THUNDERSTORMS
ARE NOW MOVING THROUGH NORTHERN PORTIONS OF BOSTON METRO AREA...AND
SHOULD SWEEP THROUGH REMAINDER OF BOSTON AREA BETWEEN 2200 AND 2300Z.
SEVERAL MEASURED GUSTS AROUND 40 KNOTS AND NUMEROUS REPORTS OF WIND
DAMAGE HAVE BEEN RECEIVED WITH THIS LINE. GIVEN MODERATE INSTABILITY
WITH MLCAPE AROUND 2000 J/KG AHEAD OF LINE...DAMAGING WINDS AND
MARGINALLY SEVERE HAIL WILL LIKELY CONTINUE FOR THE NEXT COUPLE OF
HOURS.  

..CRAVEN.. 07/01/01



SPC MESOSCALE DISCUSSION 1347 FOR NEW YORK CITY AREA/LONG
ISLAND/CT/RI/SERN MA CONCERNING...SEVERE THUNDERSTORM WATCH 491... 

VALID 012155Z - 012300Z 

INDIVIDUAL CELLS WITHIN SQUALL LINE MOVING ABOUT 260/40 KNOTS...SO
DAMAGING WINDS REMAIN A STRONG POSSIBILITY.  AS SHORT LINE OF
THUNDERSTORMS FROM NEW LONDON COUNTY CT TO SUFFOLK COUNTY NY HAS
INTENSIFIED...PORTION OF MAIN LINE FROM CENTRAL CT TO SOUTHEAST NEW YORK
HAS WEAKENED SOMEWHAT.  EXTRAPOLATION HAS LEADING LINE IN
BRISTOL/PLYMOUTH COUNTIES MA AROUND 2300Z AND DUKES COUNTY MA AROUND
2300Z.  

MAIN SQUALL LINE MOVING THROUGH NEW YORK CITY METRO AREA CURRENTLY...AND
MOST INTENSE ACTIVITY SHOULD CLEAR METRO BY ABOUT 2245Z.  

..CRAVEN.. 07/01/01



SPC MESOSCALE DISCUSSION 1348 FOR WV TO THE DEL-MAR-VA
CONCERNING...SEVERE THUNDERSTORM WATCH 492... 

VALID 012215Z - 012330Z 

THUNDERSTORMS MOVING INTO THE CHESAPEAKE BAY AREA WILL LIKELY PRODUCE
LARGE HAIL AND DAMAGING WINDS.  A SEVERE THUNDERSTORM WATCH WILL BE
ISSUED SHORTLY. 

LEADING SQUALL LINE INTENSIFYING FROM FAUQUIER COUNTY VA TO KENT COUNTY
DE IS ALONG SOUTHERN EDGE OF WEATHER WATCH.  AIRMASS IS MODERATELY
UNSTABLE FROM EASTERN VIRGINIA INTO SOUTHERN NEW JERSEY WITH MLCAPE OF
1500-2000 J/KG.  GIVEN OBSERVED 3 KM FLOW OF 30-40 KNOTS AT DOVER DE AND
WAKEFIELD VA WSR-88D SITES...POTENTIAL FOR DAMAGING WINDS APPEARS LIKELY
SOUTH OF CURRENT WEATHER WATCH. 

..CRAVEN.. 07/01/01