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MESOSCALE DISCUSSION 0431
NWS STORM PREDICTION CENTER NORMAN OK
0459 PM CDT WED APR 10 2013
AREAS AFFECTED...PORTIONS PA...ERN OH...NRN WV PANHANDLE...SERN
NY...NRN NJ.
CONCERNING...SEVERE POTENTIAL...WATCH LIKELY
VALID 102159Z - 102300Z
PROBABILITY OF WATCH ISSUANCE...80 PERCENT
SUMMARY...TWO PRIMARY/BOWING TSTM COMPLEXES -- ONE MOVING NEWD OUT
OF NERN PA...SECOND MOVING EWD FROM NERN OH -- ARE FCST TO OFFER
DAMAGING WIND POTENTIAL. EASTERN ONE WILL BE SHORTER-LIVED...MOVING
INTO MORE STABLE AIR. WESTERN COMPLEX MAY PERSIST WITH SVR THREAT
RELATIVELY MAXIMIZED NEAR OUTFLOW BOUNDARY FROM FIRST. ISOLATED TO
WIDELY SCATTERED TSTMS ALONG THEIR OUTFLOW BOUNDARIES MAY PRODUCE
OCNL HAIL AND GUSTS NEAR SVR LIMITS...BUT THREAT FROM THOSE APPEARS
MRGL/TRANSIENT. ELEVATED CONVECTION WELL N OF BOUNDARY SHOULD
REMAIN LARGELY SUB-SVR...BUT WITH ISOLATED HAIL NEAR SVR LIMITS AND
STG GUSTS. NEW WW IS BEING CONSIDERED THAT WOULD COVER WRN COMPLEX.
DISCUSSION...SFC MESOANALYSIS INDICATED COLD MARINE BOUNDARY FROM
NEAR ACY NNWWD ACROSS BUCKS COUNTY PA THAN ARCHING OVER PIKE COUNTY
PA AND SULLIVAN COUNTY NY...HAVING ALREADY PASSED MSV. THIS
BOUNDARY CORRESPONDS WELL TO FINE LINE EVIDENT IN COMPOSITE
REFLECTIVITY ANIMATIONS...MOVING WWD 5-10 KT. THIS BOUNDARY WILL BE
OVERTAKEN WITHIN NEXT 1-2 HOURS FROM N-S...BY MCS MOVING EWD 45-50
KT OVER NERN PA. QUASISTATIONARY FRONT INTERSECTED MCS OVER NERN PA
NEAR BORDER WITH SULLIVAN COUNTY NY...AND EXTENDED ENEWD ACROSS SWRN
MA. NARROW PLUME OF RELATIVELY UNDISTURBED WARM SECTOR WITH AT
LEAST MRGLLY SFC-BASED EFFECTIVE INFLOW PARCELS IS EVIDENT BETWEEN
LEADING MCS AND MARINE BOUNDARY...WITHIN WHICH MCS STILL POSES RISK
OF STG-DAMAGING GUSTS. THIS RISK WILL DIMINISH SUBSTANTIALLY WITH
EWD EXTENT INTO STABLE MARINE AIR...THOUGH BRIEF/ISOLATED
PENETRATION OF CONVECTIVE GUSTS TO SFC CANNOT BE RULED OUT AS FAR E
AS HUDSON RIVER.
OUTFLOW BOUNDARY FROM NERN PA COMPLEX WAS ANALYZED ACROSS
NORTHUMBERLAND/CAMBRIA/BEAVER COUNTIES PA INTO ERN OH...INTERSECTING
NEXT MCS BETWEEN CAK-PHD. SECOND COMPLEX EXHIBITS VERY SIMILAR
STRUCTURE AND MOVEMENT TO FIRST...BUT MORE INTENSE...PRODUCING GUSTS
TO 56 KT AT POV AT 2117Z. ITS DAMAGING-WIND THREAT SHOULD DIMINISH
WITH NWD EXTENT FROM OUTFLOW BOUNDARY...WHERE STABLE LAYER BECOMES
PROGRESSIVELY COOLER AND DEEPER. NONETHELESS...60-80 KT REAR-INFLOW
JET WAS EVIDENT IN CLE RADAR BASE VELOCITY DATA...INDICATING
CONSIDERABLE MOMENTUM FOR WIND POTENTIAL TO PERSIST INTO WRN PA.
NEAR AND S OF OUTFLOW BOUNDARY...AIR MASS IS CHARACTERIZED BY
SPORADICALLY WELL-MIXED BOUNDARY LAYERS AWAY FROM SMALLER
OUTFLOWS...SUPPORTING THREAT FOR SVR GUSTS. HOWEVER...DIABATIC SFC
COOLING WILL STABILIZE THIS AIR MASS WITH TIME AND REDUCE ALREADY
MRGL MLCAPE OF AROUND 500 J/KG. AS SUCH...DAMAGING GUST POTENTIAL
SHOULD DIMINISH WITH TIME AND EWD EXTENT ACROSS CENTRAL-ERN PA.
..EDWARDS/CORFIDI.. 04/10/2013
ATTN...WFO...OKX...PHI...BGM...CTP...PBZ...CLE...
LAT...LON 40298197 40988109 41718071 41757850 41657496 41237394
40347407 39997552 39767897 40298197
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