SPC AC 180559

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1259 AM CDT TUE JUN 18 2013

   VALID 181200Z - 191200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EARLY
   EVENING FOR SRN PARTS OF IL/IND/OH AND FAR NRN KY...

   ...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON THROUGH TONIGHT
   ACROSS SRN AND CENTRAL HIGH PLAINS INTO CENTRAL PARTS OF SD/NEB...

   ...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
   ACROSS PARTS OF CENTRAL ID INTO NWRN AND NORTH CENTRAL MT...

   ...SYNOPSIS...
   THE NERN PACIFIC CLOSED LOW AND ATTENDANT TROUGH WILL ADVANCE EWD
   INTO THE WRN STATES THIS FORECAST PERIOD TAKING ON A NEGATIVE
   TILT...WITH THE LOW CENTERED ALONG THE WA/ORE COASTS AND THE TROUGH
   EXTENDING SEWD THROUGH NV BY 12Z WED.  AN UPPER RIDGE CURRENTLY
   CENTERED OVER THE ROCKIES WILL SUBSEQUENTLY SHIFT EWD INTO THE
   PLAINS. A WEAK IMPULSE IS FORECAST TO TRACK EWD THROUGH THE RIDGE
   CROSSING THE CENTRAL ROCKIES AND REACHING THE CENTRAL PLAINS BY 12Z
   WED. MIDLEVEL FLOW IN THE NERN STATES WILL WEAKEN TODAY AS AN
   ATTENDANT SHORTWAVE TROUGH MOVES EWD FROM QUEBEC TO THE CANADIAN
   MARITIMES.  A PROMINENT SHORTWAVE TROUGH...CURRENTLY TRACKING SEWD
   THROUGH THE ERN DAKOTAS PER WATER VAPOR IMAGERY...WILL MOVE INTO THE
   LOWER OH VALLEY REGION DURING PEAK HEATING...WHILE A LOWER TN VALLEY
   TROUGH SHIFTS EWD TO THE MID ATLANTIC STATES.

   AT THE SURFACE...A COLD FRONT WILL MOVE SWD THROUGH THE OH
   VALLEY...AND SEWD THROUGH NY/PA AND SRN NEW ENGLAND.  MEANWHILE...A
   COLD FRONT ATTENDANT TO THE WRN U.S. TROUGH IS EXPECTED TO MOVE INTO
   THE NRN INTERMOUNTAIN WEST THIS AFTERNOON AND REACH WRN MT TONIGHT.

   ...OH VALLEY TO MID ATLANTIC STATES AND SRN NEW ENGLAND...
   THE COMBINATION OF SURFACE HEATING ACROSS THE OH VALLEY TODAY...
   SURFACE DEW POINTS AROUND 60 F AND MIDLEVEL LAPSE RATES OF 6.5 TO 7
   C/KM ACCOMPANYING THE ERN DAKOTAS SHORTWAVE TROUGH SHOULD RESULT IN
   A MODERATELY UNSTABLE AIR MASS FROM IL TO OH. ALTHOUGH LOW LEVEL
   CONVERGENCE MAY NOT BE TOO STRONG ALONG THE SWD MOVING FRONT...
   FORCING FOR ASCENT ATTENDANT TO THE PROGRESSIVE TROUGH IS EXPECTED
   TO SUPPORT TSTM DEVELOPMENT. MLCAPE TO AT LEAST 1000 J/KG AND
   EFFECTIVE BULK SHEAR OF 35-40 KT PARALLEL TO THE FRONT SUGGEST LINE
   SEGMENTS SHOULD BE THE PRIMARY STORM MODE...THOUGH A FEW SUPERCELLS
   WILL BE POSSIBLE. DAMAGING WINDS AND HAIL WILL BE THE PRIMARY
   THREATS...WITH ACTIVITY DIMINISHING IN INTENSITY DURING THE EVENING
   AS THE BOUNDARY LAYER STABILIZES.  

   FARTHER EAST ACROSS PA TO SRN NEW ENGLAND...TSTMS WILL BE POSSIBLE
   THROUGH THE AFTERNOON WITH A FEW ORGANIZED STORMS GIVEN 35-40 KT OF
   EFFECTIVE BULK SHEAR.  HOWEVER...WEAKER INSTABILITY SHOULD LIMIT THE
   OVERALL SEVERE WEATHER THREAT...AND PRECLUDES HIGHER PROBABILITIES
   AND THE EWD EXTENSION OF THE SLIGHT RISK.

   FORCING FOR ASCENT ATTENDANT TO THE LOWER TN VALLEY TROUGH WILL
   SPREAD ACROSS VA/MD THIS AFTERNOON/EARLY EVENING...AND SHOULD
   SUPPORT SOME TSTM DEVELOPMENT. MODEL DIFFERENCES IN THE DEGREE OF
   DESTABILIZATION PRECLUDES THE ISSUANCE OF A CATEGORICAL SLIGHT
   RISK...THOUGH 30-40 KT WLY MIDLEVEL WINDS ACCOMPANYING THE TROUGH
   COULD PROMOTE SOME STORM ORGANIZATION.  THUS...THIS OUTLOOK WILL
   EXTEND LOW SEVERE WIND/HAIL PROBABILITIES SWD ACROSS MD/VA. 

   ...CENTRAL AND SRN HIGH PLAINS TO CENTRAL SD/NEB...
   SELY LOW LEVEL WINDS ARE EXPECTED TO STRENGTHEN TO 20-25 KT ACROSS
   THE FULL EXTENT OF THE HIGH PLAINS.  TSTM DEVELOPMENT IS EXPECTED
   WITHIN THIS UPSLOPE FLOW REGIME FROM ERN NM TO ERN WY BY MID-LATE
   AFTERNOON WHERE THE AIR MASS WILL BE MODERATELY UNSTABLE.  EFFECTIVE
   BULK SHEAR UP TO 35-40 KT WILL SUPPORT ORGANIZED STORMS WITH
   SUPERCELLS POSSIBLE RESULTING IN THREATS FOR HAIL AND DAMAGING
   WINDS. A NON-ZERO TORNADO THREAT IS FORECAST ACROSS MAINLY THE
   CENTRAL HIGH PLAINS...WHERE MODELS SUGGEST AN INCREASE IN LOW LEVEL
   SHEAR DURING THE EARLY EVENING. THERE IS SOME CONFIDENCE FOR AN MCS
   TO DEVELOP THIS EVENING INTO THE PART OF THE OVERNIGHT PERIOD ACROSS
   THE WRN HALF OF NEB/SD AS LOW LEVEL WAA INCREASES ALONG THE NOSE OF
   A STRENGTHENING/VEERING LLJ.  DAMAGING WINDS AND HAIL WILL BE THE
   PRIMARY THREATS WITH THE MCS.

   ...PART OF CENTRAL ID/WRN AND NORTH CENTRAL MT...
   SURFACE DEW POINTS IN THE MID-UPPER 40S TO LOWER 50S COMBINED WITH
   SURFACE HEATING AND STEEP LAPSE RATES WILL RESULT IN MLCAPE OF AT
   LEAST 1000 J/KG ACROSS THE SLIGHT RISK AREA THIS AFTERNOON INTO THE
   EVENING. HEIGHT FALLS SPREADING EWD INTO THIS REGION IN THE
   AFTERNOON/EVENING WILL SUPPORT TSTM DEVELOPMENT WITH THE THREAT FOR
   HAIL AND DAMAGING WINDS...AS INCREASING BULK SHEAR SUPPORTS STORM
   ORGANIZATION INCLUDING A FEW SUPERCELLS.

   ..PETERS/ROGERS.. 06/18/2013

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