SPC AC 270559

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1259 AM CDT SAT JUN 27 2015

   VALID 271200Z - 281200Z

   ...THERE IS AN ENH RISK OF SVR TSTMS TODAY ACROSS THE CAROLINA AND
   VIRGINIA PIEDMONT INTO CENTRAL MARYLAND...ADJACENT SOUTHERN
   PENNSYLVANIA AND THE DELMARVA PENINSULA...

   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
   MID ATLANTIC COAST...AND THE UPPER OHIO VALLEY INTO THE CENTRAL
   APPALACHIANS...

   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTHERN PLAINS RED
   RIVER VALLEY...

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
   NORTHERN PLAINS...

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE GULF COAST REGION...

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE SOUTHERN ROCKIES
   INTO THE LOWER DESERTS OF ARIZONA...

   ...THERE IS A MRGL RISK OF SVR TSTMS EAST OF THE SOUTHERN CASCADES
   INTO PARTS OF CENTRAL OREGON...

   ...SUMMARY...
   SEVERE STORMS CAPABLE OF PRODUCING POTENTIALLY DAMAGING WIND GUSTS
   ARE EXPECTED TODAY ACROSS THE MID ATLANTIC COAST REGION...AND PARTS
   OF THE UPPER OHIO VALLEY INTO THE WESTERN SLOPES OF THE CENTRAL
   APPALACHIANS.  A COUPLE OF TORNADOES ALSO APPEAR
   POSSIBLE...PARTICULARLY ACROSS PARTS OF NORTHERN VIRGINIA AND
   CENTRAL MARYLAND INTO THE DELMARVA PENINSULA.  OTHER SEVERE STORMS
   ARE EXPECTED ACROSS THE NORTHERN PLAINS RED RIVER VALLEY...PERHAPS
   PORTIONS OF THE SOUTHERN ROCKIES INTO THE LOWER DESERTS OF
   ARIZONA...PORTIONS OF CENTRAL OREGON...AND THE GULF COAST REGION.

   ...SYNOPSIS...
   UPPER FLOW ACROSS NORTH AMERICA WILL REMAIN AMPLIFIED TODAY.  A
   SUBTROPICAL HIGH IS EXPECTED TO REMAIN PROMINENT OVER THE GREAT
   BASIN...WITH A RIDGE EXTENDING NORTHWARD ALONG AN AXIS INTO THE LEE
   OF THE CANADIAN ROCKIES.  ON THE WESTERN PERIPHERY OF THIS
   FEATURE...WEAK UPPER TROUGHING EMERGING FROM THE SUBTROPICAL EASTERN
   PACIFIC IS FORECAST TO CONTINUE DEVELOPING NORTHWARD NEAR THE
   CALIFORNIA COAST.  AT THE SAME TIME...A SIGNIFICANT IMPULSE WITHIN
   THE MID-LATITUDE WESTERLIES APPEARS LIKELY TO DIG AROUND ITS
   NORTHEASTERN PERIPHERY...ACROSS THE CENTRAL CANADIAN/U.S. BORDER
   AREA...INTO LARGE-SCALE UPPER TROUGHING CURVING ACROSS THE
   MISSISSIPPI VALLEY INTO THE ATLANTIC SEABOARD.  A MUCH STRONGER
   DOWNSTREAM IMPULSE IS FORECAST TO GRADUALLY PIVOT THROUGH THE OHIO
   VALLEY...AND ADJACENT PORTIONS OF THE LOWER GREAT LAKES REGION AND
   CENTRAL APPALACHIANS.  MODELS CONTINUE TO INDICATE THAT THIS WILL BE
   ACCOMPANIED BY SIGNIFICANT LOW/MID-LEVEL CYCLOGENESIS ACROSS THE
   UPPER OHIO VALLEY AND LOWER GREAT LAKES REGION DURING THE DAY TODAY.
    SECONDARY SURFACE LOW DEVELOPMENT IS PROBABLE TO THE LEE OF THE
   NORTH CENTRAL APPALACHIANS TONIGHT...AS THE UPPER IMPULSE TAKES ON
   MORE OF A NEUTRAL TO NEGATIVE TILT.  

   ...MID ATLANTIC COAST/UPPER OHIO VALLEY/CENTRAL APPALACHIANS...
   THE EVOLVING LARGE-SCALE PATTERN DOES APPEAR AT LEAST SOMEWHAT
   CONDUCIVE TO CONSIDERABLE CONVECTIVE POTENTIAL FOR
   TODAY...PARTICULARLY IN TERMS OF FORCING FOR LARGE-SCALE ASCENT AND
   SUFFICIENT VERTICAL SHEAR IN THE WARM SECTOR OF THE DEVELOPING
   CYCLONE.  THE WARM SECTOR...PARTICULARLY EAST OF THE CENTRAL
   APPALACHIANS...LIKELY WILL BECOME CHARACTERIZED BY SEASONABLY HIGH
   MOISTURE CONTENT.  HOWEVER...MID-LEVEL LAPSE RATES ARE NOT EXPECTED
   TO BE PARTICULARLY STEEP...RESULTING IN RATHER MODEST CAPE...AND
   MODELS SUGGEST THAT STRONGEST 850 MB WIND FIELDS MAY BE CONFINED TO
   THE COOL SIDE OF THE WARM FRONTAL ZONE.  THE FRONT INITIALLY WILL
   EXTEND ACROSS THE UPPER OHIO VALLEY INTO NORTHERN MID ATLANTIC
   COAST...AND APPEARS LIKELY TO BE REINFORCED BY WIDESPREAD
   PRECIPITATION DURING THE DAY TODAY.  

   LOW-LEVEL HODOGRAPHS THROUGH MUCH OF THE WARM SECTOR MAY REMAIN WEAK
   TO MODEST IN STRENGTH...PERHAPS LARGEST NEAR A LINGERING SURFACE
   BOUNDARY ACROSS NORTHERN VIRGINIA INTO THE DELMARVA PENINSULA...AND
   NEAR THE SURFACE CYCLONE OVER EASTERN OHIO/WESTERN
   PENNSYLVANIA...BEFORE IT OCCLUDES.  THE HIGHER BOUNDARY LAYER
   MOISTURE CONTENT EXPECTED EAST OF THE LEE SURFACE TROUGH...ACROSS
   NORTHERN/EASTERN VIRGINIA INTO THE DELMARVA PENINSULA...SEEMS TO
   OFFER SOMEWHAT BETTER POTENTIAL FOR A COUPLE OF TORNADOES IN
   DEVELOPING THUNDERSTORM ACTIVITY THIS AFTERNOON.

   OTHERWISE...DESTABILIZATION ALONG/EAST OF THE LEE SURFACE TROUGH
   ACROSS THE PIEDMONT OF THE CAROLINAS INTO VIRGINIA SEEMS TO PROVIDE
   THE PRIMARY FOCUS FOR INCREASING/CONSOLIDATING THUNDERSTORM ACTIVITY
   DURING THE MID TO LATE AFTERNOON.  HEAVY PRECIPITATION LOADING...AND
   DOWNWARD MIXING OF MOMENTUM ASSOCIATED WITH 30-40 KT MEAN
   SOUTHWESTERLY LOWER/MID TROPOSPHERIC FLOW...WILL CONTRIBUTE TO THE
   RISK FOR POTENTIALLY DAMAGING WIND GUSTS AS THE STORMS SPREAD TOWARD
   THE MID ATLANTIC COAST.

   ...NORTHERN PLAINS RED RIVER VALLEY...
   MODEST BOUNDARY LAYER MOISTENING...COUPLED WITH STEEPENING OF
   MID-LEVEL LAPSE RATES ASSOCIATED WITH THE APPROACHING DIGGING SHORT
   WAVE IMPULSE...PROBABLY WILL CONTRIBUTE TO THE DEVELOPMENT OF
   VIGOROUS THUNDERSTORM DEVELOPMENT BY LATE AFTERNOON.  STRENGTHENING
   OF NORTH NORTHWESTERLY 500 MB FLOW TO 40+ KT WILL ENHANCE THE SEVERE
   WEATHER POTENTIAL...WITH A COUPLE OF SUPERCELLS POSSIBLE...CAPABLE
   OF PRODUCING LARGE HAIL AND DAMAGING SURFACE GUSTS.  IT IS POSSIBLE
   THAT FORCING FOR UPWARD VERTICAL MOTION MAY BE SUFFICIENT TO SUPPORT
   CONSOLIDATION AND UPSCALE GROWTH OF CONVECTION INTO A SOUTHWARD
   ADVANCING ORGANIZED CLUSTER OF STORMS...BEFORE ACTIVITY WEAKENS THIS
   EVENING.

   ...INTERMOUNTAIN WEST/ROCKIES...
   STEEP LOWER/MID TROPOSPHERIC LAPSE RATES...SUFFICIENT MOISTURE...
   AND LARGE-SCALE FORCING FOR ASCENT ASSOCIATED WITH IMPULSES
   MIGRATING AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE ARE EXPECTED
   TO CONTRIBUTE TO THUNDERSTORM ACTIVITY TODAY.  THIS APPEARS MOST
   LIKELY ON THE SOUTHERN PERIPHERY OF THE RIDGE...ACROSS THE NORTHERN
   ROCKIES INTO THE LOWER DESERTS OF ARIZONA...AND ACROSS THE
   NORTHWESTERN PERIPHERY...TO THE EAST OF THE SOUTHERN
   CASCADES...WHERE STRONGEST STORMS MAY BE ACCOMPANIED BY STRONG WIND
   GUSTS AND SOME HAIL.

   ..KERR/LEITMAN.. 06/27/2015

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