SPC AC 131955

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0255 PM CDT TUE AUG 13 2013

   VALID 132000Z - 141200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE NRN HIGH
   PLAINS...

   ...NC THROUGH MID ATLANTIC REGION...

   THE SLIGHT RISK FOR THIS REGION HAS BEEN DOWNGRADED TO A SEE TEXT.
   SCATTERED STORMS ARE DEVELOPING ALONG THE SRN AND CNTRL APPALACHIANS
   AND IN CAROLINAS PRE-FRONTAL WARM SECTOR. THESE STORMS ARE
   INITIATING IN AN ENVIRONMENT WITH MOIST THERMODYNAMIC
   PROFILES...WEAK CAPPING...WEAK LAPSE RATES...MODEST /1000-1500 J/KG/
   MLCAPE AND HIGH PRECIPITABLE WATER. THE BROAD CYCLONIC CIRCULATION
   AROUND THE ERN U.S. UPPER TROUGH IS CONTRIBUTING TO MODEST 25-35 KT
   UNIDIRECTIONAL WLY SHEAR PROFILES SUPPORTIVE OF MOSTLY MULTICELL
   MODES IN NC. THIS ENVIRONMENT APPEARS ONLY MARGINALLY FAVORABLE FOR
   AN ORGANIZED SEVERE THREAT. AS LOW LEVEL LAPSE RATES
   STEEPEN...ISOLATED STORMS MIGHT PRODUCE LOCALLY STRONG TO DAMAGING
   WIND GUSTS. HOWEVER...OVERALL COVERAGE OF ANY SEVERE EVENTS ARE
   EXPECTED TO REMAIN SOMEWHAT SPARSE.

   THE ATMOSPHERE MAY BE EXPERIENCING TEMPORARY LARGE SCALE SUBSIDENCE
   FARTHER NORTH INTO PORTIONS OF THE MID ATLANTIC IN WAKE OF EARLY
   MORNING MCV. HOWEVER...THE BOUNDARY LAYER IS DESTABILIZING...AND
   STORMS MAY EVENTUALLY INCREASE IN COVERAGE FROM VA NWD INTO SERN PA
   AND NJ. WIND PROFILES IN THIS REGION REMAIN SOMEWHAT STRONGER THAN
   FARTHER SOUTH WITH 35-40 KT WLY UNIDIRECTIONAL 0-6 KM SHEAR...AND A
   FEW STORMS COULD PRODUCE LOCALLY STRONG TO DAMAGING WIND GUSTS. THE
   MARGINAL THERMODYNAMIC ENVIRONMENT SHOULD SERVE AS A LIMITING FACTOR
   FOR AN ORGANIZED SEVERE EVENT.

   ...ELSEWHERE...

   ONLY MINOR ADJUSTMENTS HAVE BEEN MADE TO CURRENT FORECAST.

   ..DIAL.. 08/13/2013

   .PREV DISCUSSION... /ISSUED 1130 AM CDT TUE AUG 13 2013/

   ...SYNOPSIS...
   WITHIN A SOMEWHAT AMPLIFIED CYCLONIC MID-LEVEL FLOW REGIME...NOW
   ENCOMPASSING MUCH OF EASTERN NORTH AMERICA...A VIGOROUS SHORT WAVE
   TROUGH IS FORECAST TO DIG SOUTHEAST OF THE UPPER GREAT LAKES REGION
   DURING THE DAY...BEFORE TURNING EASTWARD ACROSS THE LOWER GREAT
   LAKES REGION...TOWARD THE NORTHERN ATLANTIC COAST TONIGHT.  AS THIS
   OCCURS...AN INTRUSION OF SUBSTANTIVELY COOLER AND DRIER LOW-LEVEL
   AIR WILL CONTINUE TO ADVANCE SOUTHEAST OF THE UPPER MIDWEST AND
   GREAT LAKES REGION...WITH THE COLD FRONT LIKELY TO REACH THE
   SOUTHERN MID ATLANTIC COAST STATES...TENNESSEE VALLEY AND OZARKS
   PLATEAU BY 12Z WEDNESDAY.  

   AT THE SAME TIME...THE CONVECTIVELY REINFORCED REMNANTS OF A
   PRECEDING FRONT WILL CONTINUE TO ADVANCE SLOWLY SOUTHWARD THROUGH
   THE GULF COAST STATES AND SOUTH CENTRAL INTO SOUTHERN PLAINS...
   GENERALLY TO THE SOUTH OF A BELT OF SEASONABLY STRONG HIGH LEVEL
   FLOW ON THE NORTHERN PERIPHERY OF FLAT SUBTROPICAL RIDGING. 
   MID-LEVEL RIDGING TO THE NORTH OF THIS LATTER FEATURE...ACROSS MUCH
   OF THE INTERMOUNTAIN WEST INTO THE PLAINS...MAY BEGIN TO WEAKEN IN
   RESPONSE TO SEVERAL WEAK IMPULSES PROGRESSING AROUND ITS
   CREST...ACROSS THE NORTHERN ROCKIES...IN ADVANCE OF A SIGNIFICANT
   CLOSED LOW APPROACHING THE PACIFIC NORTHWEST COAST.

   IN RESPONSE TO THESE DEVELOPMENTS...SEASONABLY HIGH MOISTURE CONTENT
   AIR HAS BECOME CONFINED TO PORTIONS OF THE LOWER SOUTHERN PLAINS
   INTO THE CENTRAL AND EASTERN GULF STATES...AS WELL AS PORTIONS OF
   THE MID ATLANTIC COAST.  AND STEEP MID-LEVEL LAPSE RATES...EAST OF
   THE ROCKIES...REMAIN CONFINED TO PORTIONS OF THE NORTHERN PLAINS. 
   SOME STEEPENING OF LAPSE RATES WILL OCCUR WITH STRONG MID-LEVEL
   COOLING ACCOMPANYING THE GREAT LAKES TROUGH...BUT THIS WILL BE
   MOSTLY POST-FRONTAL.

   ...SOUTHERN NEW ENGLAND INTO MID ATLANTIC COAST STATES...
   THE POTENTIALLY MOST SUBSTANTIVE SEVERE WEATHER THREAT FOR THE DAY
   APPEARS TO HAVE DIMINISHED/SHIFTED EAST OF NORTHERN MID ATLANTIC
   COASTAL AREAS THIS MORNING.  IN ADVANCE OF THE GREAT LAKES UPPER
   TROUGH...A LOWER AMPLITUDE IMPULSE...WITH A BELT OF ENHANCED
   LOWER/MID TROPOSPHERIC FLOW...HAS SHIFTED OFFSHORE.  ASSOCIATED
   ORGANIZED STRONG/SEVERE STORM DEVELOPMENT...INCLUDING
   SUPERCELLS...APPEARS INCREASINGLY CERTAIN TO REMAIN SOUTH OF
   SOUTHERN NEW ENGLAND COASTAL AREAS.  HOWEVER...MODELS DO CONTINUE TO
   INDICATE THAT A SECONDARY SURFACE LOW WILL FORM IN ASSOCIATION WITH
   THE APPROACHING TROUGH...AND MIGRATE NORTHEASTWARD ACROSS PARTS OF
   SOUTHERN NEW ENGLAND LATER TODAY AND TONIGHT.  IF THIS
   OCCURS...FAVORABLY TIMED WITH AT LEAST SOME BOUNDARY LAYER HEATING
   AND DESTABILIZATION...IT STILL DOES NOT APPEAR OUT OF THE QUESTION
   THAT THE ENVIRONMENT MAY BECOME SUPPORTIVE OF AT LEAST LOW SEVERE
   THUNDERSTORM POTENTIAL.

   FARTHER TO THE SOUTH AND WEST...VEERING AND WEAKENING OF LOW/MID
   LEVEL WIND FIELDS APPEAR TO BE ENDING LOW TORNADIC POTENTIAL. 
   HOWEVER...THE PRE-FRONTAL ENVIRONMENT REMAINS SEASONABLY MOIST
   ACROSS MUCH OF EASTERN NORTH CAROLINA AND SOUTHEAST VIRGINIA INTO
   THE DELMARVA PENINSULA...WHERE INSOLATION IS SUPPORTING MODERATELY
   LARGE CAPE.  ALTHOUGH DEEP LAYER FLOW AND SHEAR ARE WEAKENING...THEY
   MAY REMAIN STRONG ENOUGH TO SUPPORT SLIGHT RISK SEVERE
   PROBABILITIES...THOUGH FORCING FOR ORGANIZED CONVECTIVE DEVELOPMENT
   IS BECOMING INCREASINGLY UNCLEAR.

   ...NORTHERN HIGH PLAINS...
   BENEATH STEEP MID-LEVEL LAPSE RATES...SOUTHEASTERLY LOW-LEVEL FLOW
   IS EXPECTED TO MAINTAIN SUFFICIENT LOW-LEVEL MOISTURE TO SUPPORT AT
   LEAST MODERATE CAPE BY LATE AFTERNOON.  ALTHOUGH SHEAR IS EXPECTED
   TO REMAIN GENERALLY WEAK TO MODEST IN
   STRENGTH...FORCING...ASSOCIATED WITH WEAK PERTURBATIONS/CYCLONIC
   VORTICITY MAXIMA ROUNDING THE UPPER RIDGE...MAY CONTRIBUTE TO ONE OR
   TWO SMALL STORM CLUSTERS CAPABLE OF GENERATING SEVERE WIND
   GUSTS...IN ADDITION TO HAIL.

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