SPC AC 272017
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0317 PM CDT WED AUG 27 2003
VALID 272000Z - 281200Z
THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 45 S
WAL RIC HTS 45 NE CRW HLG PIT PSB 20 SSW JFK
THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 40 E
RRT RWF 30 SSW YKN BUB MHN CDR 35 SE 81V REJ P24 55 NW MOT
GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 25 ENE ECG RWI SOP
CAE 10 SSW AGS 50 WNW SAV 10 SSE SSI ...CONT... 10 ENE CRP 55 NW LRD
...CONT... CZZ PMD 10 NNW NID ELY 10 NE ENV 10 SE SUN S80 40 N FCA
...CONT... 10 SW CMX 25 S IWD 10 SSW RST FOD LWD 30 N IRK 30 SSE BRL
BMI SBN BUF SYR 30 S BTV 15 NE EFK
...THERE IS A SLGT RISK OF SVR TSTMS THRU EARLY EVE ACROSS THE
NORTHERN MID ATLANTIC COAST STATES....
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND TONIGHT
ACROSS PARTS OF THE NORTHERN PLAINS....
...OHIO VALLEY INTO MID ATLANTIC COAST...
WATER VAPOR IMAGERY SUPPORTS MODEL PROGS INDICATING SEVERAL WAVES
EMBEDDED WITHIN WEAK SUBTROPICAL BRANCH OF THE WESTERLIES...WHICH
CURVES CYCLONICALLY FROM THE NORTH CENTRAL PLAINS THROUGH THE LOWER
OHIO VALLEY INTO THE MID ATLANTIC STATES. ONE WAVE IS PROGRESSING
OUT OF THE LOWER OHIO VALLEY INTO THE CENTRAL APPALACHIANS...AND
WILL CONTINUE EASTWARD ACROSS MID ATLANTIC COAST AREAS THIS EVENING.
THIS IS JUST TO THE SOUTH OF STRONG POLAR JET...REMAINING NEAR THE
CANADIAN U.S. BORDER...WITH EMBEDDED VIGOROUS SHORT WAVE TROUGH
SWEEPING ACROSS QUEBEC AND THE ST. LAWRENCE VALLEY. CONFIGURATION
OF UPPER FEATURES HAS CONTRIBUTED TO STRONG DIVERGENT UPPER FLOW
FIELD...WHICH HAS SUPPORTED EVOLUTION OF CONVECTIVE CLUSTER NOW
SPREADING ACROSS PARTS OF SOUTHWESTERN PENNSYLVANIA AND NORTHERN
WEST VIRGINIA.
CONVECTIVE SYSTEM APPEARS LIKELY TO CONTINUE EVOLVING/INTENSIFYING
LATE THIS AFTERNOON AS IT PROGRESSES EAST OF THE NORTH CENTRAL
APPALACHIANS INTO MOIST AND MODERATELY UNSTABLE ENVIRONMENT ACROSS
THE NORTHERN MID ATLANTIC COAST STATES. CONVECTIVELY GENERATED
THERMAL BOUNDARY EXTENDING FROM THE EASTERN WEST VIRGINIA PANHANDLE
THROUGH NORTHERN VIRGINIA WILL PROVIDE A FOCUS FOR PROPAGATION OF
STORMS...AIDED BY 30 TO 40 KT MID-LEVEL FLOW ON SOUTHERN FRINGE OF
STRONGER WESTERLIES. THERMODYNAMIC ENVIRONMENT REMAINS SUFFICIENT
FOR THE DEVELOPMENT OF A SUBSTANTIAL COLD POOL/ MESO
HIGH...ACCOMPANIED BY GUSTY/DAMAGING WINDS IN WAKE OF ASSOCIATED
GUST FRONT...WHICH WILL PROGRESS OFFSHORE DURING THE MID EVENING
HOURS.
OTHERWISE...DAYTIME HEATING/WEAKENING CAP HAS ALLOWED SCATTERED
CONVECTIVE DEVELOPMENT ALONG/AHEAD OF STALLING SURFACE COLD FRONT
ACROSS THE LOWER OHIO VALLEY. FLOW FIELDS/VERTICAL SHEAR PROFILES
HAVE BECOME QUITE WEAK ACROSS THIS REGION...WITH MAIN SHORT WAVE NOW
PROGRESSING INTO THE EASTERN CANADIAN PROVINCES. THIS APPEARS
LIKELY TO MINIMIZE OVERALL SEVERE THREAT WITH THIS ACTIVITY...WHICH
SHOULD DIMINISH WITH LOSS OF DAYTIME HEATING.
...NORTHERN PLAINS...
SHORT WAVE TROUGH LIFTING OUT OF THE NORTH CENTRAL ROCKIES...AND
UPSTREAM SHORT WAVE ALONG THE NORTHWESTERN CANADIAN/U.S. BORDER WILL
CONTINUE TO GRADUALLY EVOLVE INTO LARGER SCALE TROUGH...WHILE
PROGRESSING EASTWARD LATE THIS AFTERNOON AND TONIGHT. LOW-LEVEL
CYCLOGENESIS IS ALREADY OCCURRING ACROSS THE NORTH CENTRAL HIGH
PLAINS IN RESPONSE TO THIS. DEEPENING SURFACE LOW WILL BECOME
CENTERED OVER THE WESTERN DAKOTAS BY EARLY THIS EVENING...AND MAY
BECOME FOCUS FOR HIGH BASED CONVECTIVE CLUSTER. MEAN MIXED LAYER
CAPE ON NOSE OF LOW-LEVEL THERMAL RIDGE ACROSS SOUTHWESTERN NORTH
DAKOTA AND WESTERN SOUTH DAKOTA IS NOT PARTICULARLY STRONG...BUT
DEEP MIXED BOUNDARY LAYER WITH LARGE TEMPERATURE/DEW POINT SPREADS
WILL CONTRIBUTE TO POTENTIAL FOR DAMAGING WIND GUSTS.
THIS ACTIVITY SHOULD DIMINISH WITH LOSS OF DAYTIME HEATING...BUT
CONVECTION SHOULD INCREASING LATE THIS EVENING/OVERNIGHT...ALONG/
NORTH OF SURFACE WARM FRONT...NEAR THE NORTH DAKOTA/MANITOBA BORDER.
MODEL FORECAST SOUNDINGS SUGGEST CAPE FOR PARCELS LIFTED ABOVE
LOW-LEVEL INVERSION LAYER ON THE ORDER OF 1000 TO 2000 J/KG. THIS
WILL BE SUPPORTIVE OF VIGOROUS UPDRAFTS WITH POTENTIAL FOR LARGE
HAIL IN FAVORABLY SHEARED ENVIRONMENT. STRONGER LOW-LEVEL WARM
ADVECTION REGIME AND ASSOCIATED CONVECTION ON NOSE OF 30 TO 50 KT
LOW-LEVEL JET WILL SPREAD EASTWARD INTO WESTERN ONTARIO AND EXTREME
NORTHERN MINNESOTA OVERNIGHT.
..KERR.. 08/27/2003
...NOTICE...
FOR USERS DECODING THE POINTS PARAGRAPH HEREIN...LATITUDE AND
LONGITUDE POINTS FOR THE CATEGORICAL AND PROBABILISTIC OUTLOOK
GRAPHICS ALSO ARE LOCATED IN A SEPARATE PRODUCT UNDER THE WMO
HEADINGS WUUS01 PTSDY1...WUUS02 PTSDY2...AND WUUS03 PTSDY3. THE
INCLUSION OF POINTS IN THIS PRODUCT WILL EVENTUALLY BE DISCONTINUED.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED FOR 0100Z
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