SPC AC 180554
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1254 AM CDT SAT MAY 18 2013
   
   VALID 181200Z - 191200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS FOR PARTS OF WRN OK AND WRN
   KS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FOR A LARGE PORTION OF THE
   PLAINS STATES...
   
   ...AN ACTIVE SEVERE WEATHER DAY IS EXPECTED OVER A LARGE PORTION OF
   THE PLAINS.  LARGE DESTRUCTIVE HAIL AND THE POSSIBILITY FOR A FEW
   STRONG TORNADOES ARE THE MAIN THREATS...
   
   ...SYNOPSIS...
   INCREASING CYCLONIC MID-UPPER FLOW WILL OVERSPREAD MUCH OF THE
   PLAINS THROUGH THE DAY 1 PERIOD DOWNSTREAM OF AN APPROACHING LARGER
   SCALE WRN U.S. TROUGH.  THE PRIMARY UPPER TROUGH AXIS WILL MOVE FROM
   THE GREAT BASIN TO THE CNTRL ROCKIES-SRN HIGH PLAINS BY SUNDAY
   MORNING.  AN ELONGATED LEE TROUGH WILL CONSOLIDATE INTO A LOW
   FORECAST INVOF THE ERN CO/WRN KS BORDER BY 00Z/19.  A MOISTURE RICH
   RESERVOIR OVER THE SRN PLAINS WILL CONTINUE TO BE DRAWN NWWD INTO
   PORTIONS OF THE CNTRL HIGH PLAINS E OF A SHARPENING DRYLINE BY
   AFTERNOON.  SEVERE STORMS ARE EXPECTED TO DEVELOP DURING THE
   AFTERNOON-EVENING HOURS WITH SOME OF THESE STORMS CONTINUING WELL
   AFTER DARK.
    
   ...PLAINS...
   FRIDAY EVENING WATER VAPOR IMAGERY SHOWS A LEAD SHORTWAVE TROUGH
   OVER SRN NM AND THIS FEATURE IS FORECAST TO MOVE INTO CNTRL KS-OK BY
   EARLY-MID AFTERNOON.  DESPITE IMPLIED SUBSIDENCE IN ITS WAKE...THE
   APPROACH OF THE LARGER SCALE TROUGH AND ASSOCIATED HEIGHT FALLS
   /FORCING FOR ASCENT/ WILL OVERSPREAD THE HIGH PLAINS DURING THE
   AFTERNOON-EVENING.  BENEATH THE STOUT EML...HIGH QUALITY BOUNDARY
   LAYER MOISTURE SAMPLED BY RAOBS OVER THE SRN PLAINS FRIDAY EVENING
   /15-16 G/KG 100MB MEAN MIXING RATIO/...WILL LEAD TO DEWPOINTS
   RANGING FROM THE LOWER 60S OVER THE DAKOTAS TO THE UPPER 60S AND
   LOWER 70S FARTHER S OVER OK/KS BY MID AFTERNOON.  STRONG DIABATIC
   HEATING ALONG THE DRYLINE WILL CONSIDERABLY WEAKEN AN INITIALLY
   STOUT CAP BY MID-LATE AFTERNOON.  VERY STEEP MID LEVEL LAPSE RATES
   IN EXCESS OF 8-9 DEG C/KM IN COMBINATION WITH THIS RICH MOISTURE
   WILL CONTRIBUTE TO MODERATE INSTABILITY OVER PARTS OF THE NRN PLAINS
   TO EXTREME INSTABILITY /4000-5000 J/KG MLCAPE/ OVER PARTS OF KS INTO
   NWRN TX. 
    
   ONCE THE CAP IS ERODED IN POCKETS ALONG THE DRYLINE...EXPLOSIVE
   UPDRAFTS WILL RAPIDLY BECOME SEVERE AND INITIALLY FAVOR LARGE TO
   VERY LARGE HAIL AND DMGG WINDS.  SUFFICIENT DEEP LAYER SHEAR
   /RANGING FROM AROUND 30 KT FROM NWRN TX TO WELL INTO THE SUPERCELL
   RANGE FROM KS NWD/ WILL PROMOTE DISCRETE SUPERCELLS AS THE EARLY
   CONVECTIVE MODE.  BY THE 00Z-04Z PERIOD...STRONGER LOW LEVEL MASS
   RESPONSE IN THE FORM OF A STRENGTHENING LLJ E AND SE OF THE KS/CO
   LOW OVER PARTS OF WRN KS AND WRN OK...WILL ACT TO ENLARGE HODOGRAPHS
   /200-500 M2/S2 EFFECTIVE SRH/ DURING THIS TIMEFRAME.  AS A
   RESULT...SUPERCELL TORNADO POTENTIAL APPEARS HIGHEST DURING THE
   EVENING WITH PERHAPS A STRONG TORNADO OR TWO OCCURRING.  UPSCALE
   GROWTH MAY EVENTUALLY OCCUR WITH ANY PERSISTENT OR REGENERATIVE
   CLUSTER OF SUPERCELLS WITH A LINGERING OVERNIGHT THREAT FOR A FEW
   TORNADOES AND DMGG WINDS. 
   
   ...SRN APPALACHIANS...
   A WEAKENING MID LEVEL TROUGH OVER THE SRN APPALACHIANS VICINITY WILL
   LIKELY PROVIDE AN IMPETUS FOR DIURNALLY-DRIVEN STORMS AS SURFACE
   HEATING LEADS TO THE POSSIBILITY FOR A FEW STRONG STORMS CAPABLE OF
   LOCALLY DMGG WIND.  THIS ACTIVITY WILL LIKELY WANE IN INTENSITY BY
   THE EVENING AS THE BOUNDARY LAYER STABILIZES.
   
   ..SMITH/MARSH.. 05/18/2013
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z