SWODY1
SPC AC 111927
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0227 PM CDT MON OCT 11 2010
VALID 112000Z - 121200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND TONIGHT
ACROSS PARTS OF THE LWR GREAT LAKES REGION INTO NRN MID ATLANTIC
COASTAL AREAS...
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS
PARTS OF THE SRN PLAINS...
...20Z UPDATE...
OUTLOOK AREAS HAVE BEEN ADJUSTED IN AN ATTEMPT TO BETTER ACCOUNT FOR
ONGOING TRENDS CONCERNING DESTABILIZATION AND THE LIKELIHOOD OF
THUNDERSTORM DEVELOPMENT.
...LWR GREAT LAKES INTO NRN MID ATLANTIC COAST/SRN NEW ENGLAND...
FRONTAL ZONE ACROSS SOUTHERN NEW YORK AND NORTHERN PENNSYLVANIA NOW
APPEARS MOSTLY LIKELY TO PROVIDE THE PRIMARY FOCUS FOR CONVECTIVE
DEVELOPMENT THROUGH THE REMAINDER OF THE FORECAST PERIOD. STRONGEST
FORCING FOR UPWARD VERTICAL MOTION MAY NOT DEVELOP UNTIL THIS
EVENING...IN ASSOCIATION WITH THE APPROACH OF A DIGGING UPSTREAM
SHORT WAVE TROUGH. BUT SCATTERED STORMS ARE ALREADY DEVELOPING IN
THE PRESENCE OF WEAK TO MODERATE CAPE /UP TO AROUND 1000 J PER KG/
AND A MODESTLY SHEARED 30-40 KT WEST NORTHWESTERLY DEEP LAYER MEAN
FLOW. THERE APPEARS TO BE POTENTIAL FOR ORGANIZING STORM CLUSTERS
CAPABLE OF PRODUCING POTENTIALLY DAMAGING SURFACE GUSTS...IN
ADDITION TO HAIL...WHICH COULD IMPACT PARTS OF THE GREATER NEW YORK
METROPOLITAN AREA THIS EVENING.
...SOUTHERN PLAINS...
A NARROW CORRIDOR OF STRONGER DESTABILIZATION CONTINUES TO DEVELOP
ALONG AN AXIS NEAR A WEAK SURFACE FRONT/TROUGH EXTENDING FROM
CENTRAL TEXAS NORTHWARD THROUGH EASTERN OKLAHOMA AND SOUTHEAST
KANSAS. THIS ENVIRONMENT APPEARS THE MOST CONDUCIVE TO THE RISK FOR
STRONG/SEVERE CAPABLE OF PRODUCING HAIL AND STRONG SURFACE GUSTS
THROUGH EARLY EVENING. AND SEVERE PROBABILITIES HAVE BEEN ADJUSTED
ACCORDINGLY.
..KERR.. 10/11/2010
.PREV DISCUSSION... /ISSUED 1106 AM CDT MON OCT 11 2010/
...SYNOPSIS...
COLD UPPER LOW NCENTRAL KS CONTINUES SLOWLY SEWD INTO NERN OK 12Z
TUE. AIR MASS REMAINS MOIST IN ADVANCE OF THE LOW ACROSS ERN OK INTO
WRN AR. OVERNIGHT MCS NOW WEAKENING OVER NERN TX AND CLEARING IN
ITS WAKE WILL ALLOW INSTABILITY TO REDEVELOP AHEAD OF UPPER LOW THIS
AFTERNOON.
STALLED FRONTAL BOUNDARY WNW/ESE ACROSS PA/NJ IN CONFLUENT FLOW
BETWEEN TROUGH DROPPING SEWD FROM GREAT LAKES AND WESTERLIES IN SRN
BRANCH ACROSS THE MID ATLANTIC STATES. STEEP LAPSE RATES...MDT
SHEAR AND INSTABILITY SUFFICIENT FOR A SEVERE THUNDERSTORM THREAT
VICINITY AND JUST S OF FRONTAL ZONE.
...SRN PLAINS...
WITH THE CLEARING IN THE WAKE OF THE MCS OVER NERN TX...AND THE COOL
STEEP LAPSE RATES/7-8C/KM/ IN PLACE IN ADVANCE OF THE UPPER
LOW...SURFACE HEATING AND NEAR ONE INCH PWAT SHOULD LEAD TO
SCATTERED THUNDERSTORMS BY MID AFTERNOON. WHILE MLCAPES WILL BE
LIMITED WITH AND JUST AHEAD OF THE UPPER LOW ITSELF...FURTHER SE
ACROSS ERN OK INTO WRN AR BOTH THE INSTABILITY AND SHEAR EXPECTED TO
SUPPORT A FEW SEVERE THUNDERSTORMS AS MLCAPE CLIMBS TO 1500 J/KG AND
DEEP LAYER SHEAR FROM 30-40KT WILL BE IN PLACE. PRIMARY THREAT WILL
BE LARGE HAIL THIS AREA WITH HAIL STILL LIKELY FURTHER N WITH UPPER
LOW...BUT LESS RISK OF SEVERE.
FURTHER S THE OUTFLOW FROM THE MORNING MCS WILL BE FOCUS FOR RENEWAL
OF ACTIVE THUNDERSTORMS ERN TO SCENTRAL TX WHERE LOW LEVEL
MOISTURE...I.E. DEWPOINTS INTO THE LOW/MID 60S...COUPLED WITH LAPSE
RATES IN EXCESS OF 7C/KM...WILL PROVIDE MDT INSTABILITY.
LOW/MID LEVEL SHEAR WILL BE MARGINAL FOR ORGANIZED STORMS...HOWEVER
WITH THE LOW LEVEL CONVERGENCE ALONG OUTFLOW
BOUNDARY...THUNDERSTORMS SHOULD BECOME QUITE ACTIVE BY MID/LATE
AFTERNOON WITH A FEW SEVERE. PRIMARY THREAT GIVEN THE LIMITED SHEAR
WOULD BE LARGE HAIL.
...PA AND DELMARVA...
HAVE EXPANDED THE SLIGHT RISK SWD INTO THE DC AREA GIVEN THE
OBSERVED AIR MASS CHARACTERISTICS ON THE 12Z IAD SOUNDING AND
CURRENT OBJECTIVE ANALYSES OF THE PRE FRONTAL AIR MASS ACROSS PA
INTO DELMARVA. OVERALL MOISTURE IS LIMITED...HOWEVER...INCREASED
DIABATIC WARMING IN THE BOUNDARY LAYER COUPLED WITH 500 MB
TEMPERATURES COOLING TO -16 TO -17 C WILL CONTRIBUTE TO STEEP LAPSE
RATES WITH AFTERNOON MLCAPE VALUES APPROACHING 500-1000 J/KG WITH A
DECREASING CAP. LATEST MESOSCALE AND CONVECTION-RESOLVING MODEL
GUIDANCE ARE IN GENERALLY GOOD AGREEMENT IN SUGGESTING THAT
SURFACE-BASED STORM DEVELOPMENT WILL BECOME INCREASINGLY LIKELY BY
21Z ALONG THE COLD FRONT OVER WRN AND CNTRL PARTS OF PA. STORMS
SHOULD INCREASE IN COVERAGE THROUGH THE REMAINDER OF THE AFTERNOON
INTO TONIGHT WHILE MOVING/DEVELOPING EWD TO OFF THE NJ COAST.
PRIMARY THREAT WILL BE WIND DAMAGE AND HAIL AS STORMS EVOLVE INTO
SHORT LINE SEGMENTS/ BOWS IN THE 40-45KT WLY SHEAR ENVIRONMENT.
FURTHER S THE PRIMARY CONCERN IS STORM INITIATION AS LOW LEVEL
CONVERGENCE IS WEAK IN WLY FLOW. A FEW STORMS HOWEVER COULD DEVELOP
OFF THE HIGHER TERRAIN NRN VA/WRN MD BY PEAK HEATING AND MOVE
EASTWARD WHERE INSTABILITY AND SHEAR WILL BE FAVORABLE FOR SEVERE
STORMS.
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