SPC AC 210559
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1259 AM CDT TUE MAY 21 2013
   
   VALID 211200Z - 221200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF SW AR...SE
   OK...NW LA...CNTRL TX AND NE TX...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
   PLAINS...OZARKS...MID MS VALLEY...OH VALLEY AND GREAT LAKES...
   
   ...SRN PLAINS/ARKLATEX/MID-MS VALLEY...
   AN UPPER-LEVEL TROUGH WILL MOVE EWD FROM THE SRN ROCKIES INTO THE
   SRN PLAINS TODAY. AT THE SFC...A COLD FRONT WILL ADVANCE SEWD ACROSS
   CNTRL OK AND WCNTRL TX. AHEAD OF THE FRONT...SFC DEWPOINTS ACROSS
   THE WARM SECTOR SHOULD BE IN THE MID TO UPPER 60S F RESULTING IN
   MODERATE TO STRONG INSTABILITY BY THIS AFTERNOON. THUNDERSTORMS ARE
   FORECAST TO BE ONGOING AT THE START OF THE PERIOD ACROSS ERN OK
   WHERE AN ISOLATED THREAT FOR HAIL AND WIND DAMAGE MAY EXIST THIS
   MORNING. WITH SFC HEATING...NEW THUNDERSTORMS ARE FORECAST TO
   INITIATE ALONG AND AHEAD OF THE COLD FRONT FROM WRN AR SWWD INTO
   NORTH TX AROUND MIDDAY. THE MODELS QUICKLY EXPAND THUNDERSTORM
   COVERAGE WITH AN MCS ORGANIZING AND MOVING SEWD ACROSS THE MODERATE
   RISK AREA. STRONG INSTABILITY...STEEP MID-LEVEL LAPSE RATES AND
   MODERATE TO STRONG DEEP LAYER SHEAR SHOULD BE SUPPORTIVE OF
   WIDESPREAD SEVERE THUNDERSTORM DEVELOPMENT ACROSS THE MODERATE RISK
   AREA WHERE A SIGNIFICANT SEVERE WEATHER EVENT WILL BE POSSIBLE.
   
   FORECAST SOUNDINGS AT 00Z/WED FROM LITTLE ROCK SWWD TO AROUND THE
   DALLAS FORT WORTH METROPLEX SHOW MLCAPE VALUES OF 2500 TO 4000 J/KG
   WITH 0-6KM SHEAR OF 45 TO 55 KT. THIS ALONG WITH 850 TO 500 MB LAPSE
   RATES AROUND 7.5 C/KM SHOULD RESULT IN A POTENTIAL FOR SUPERCELLS
   WITH LARGE HAIL. HAILSTONES OF GREATER THAN 2 INCHES IN DIAMETER
   WILL BE POSSIBLE WITH THE MORE INTENSE SUPERCELLS. IN ADDITION...THE
   MORE DOMINANT SUPERCELLS SHOULD BE CAPABLE OF PRODUCING TORNADOES AS
   THE LOW-LEVEL JET STRENGTHENS. A FEW STRONG TORNADOES COULD OCCUR
   NEAR THE LOW-LEVEL JET AS BOUNDARY LAYER SHEAR BECOMES MORE
   FAVORABLE DURING THE EARLY EVENING. THE MODELS SUGGEST CELLS MAY BE
   DISCRETE AT THE START OF THE EVENT WITH A TRANSITION TO A
   SQUALL-LINE. THIS WOULD MAKE THE WIND DAMAGE THREAT INCREASINGLY
   DOMINANT AS A LINEAR MCS ORGANIZES EARLY THIS EVENING. FOR THIS
   REASON...AN ENHANCED WIND DAMAGE THREAT WILL BE POSSIBLE ACROSS THE
   MODERATE RISK AREA.
   
   ...GREAT LAKES/OH VALLEY...
   SOUTHWEST FLOW WILL BE IN PLACE TODAY FROM THE MID-MS VALLEY NEWD
   INTO THE GREAT LAKES REGION. AT THE SFC...A LOW IS FORECAST TO MOVE
   EWD ACROSS THE UPPER MS VALLEY WITH A CORRIDOR OF LOW-LEVEL MOISTURE
   EXTENDING NNEWD FROM THE LOWER OH VALLEY INTO LOWER MI. SFC
   DEWPOINTS ACROSS SRN IL...NW IND AND LOWER MI SHOULD BE IN THE MID
   60S F RESULTING IN MODERATE DESTABILIZATION. MODEL FORECASTS
   INITIATE STORMS BY MID AFTERNOON ALONG THE INSTABILITY AXIS WITH
   STORMS MOVING NEWD ACROSS THE REGION. FORECAST SOUNDINGS ALONG THE
   INSTABILITY AXIS WEST OF DETROIT AND NORTH OF INDIANAPOLIS AT 21Z
   SHOW MLCAPE VALUES IN THE 1000 TO 2000 J/KG RANGE WITH STEEP
   LOW-LEVEL LAPSE RATES AND UNIDIRECTIONAL WIND PROFILES. THIS
   ENVIRONMENT SHOULD BE FAVORABLE FOR WIND DAMAGE AS CELLS INCREASE IN
   COVERAGE THIS AFTERNOON. SEVERAL MODEL FORECASTS SHOW AN ENHANCED
   SEVERE THREAT ACROSS LOWER MI TO THE SOUTHEAST OF THE SFC LOW AND ON
   THE NOSE OF THE LOW-LEVEL JET. FOR THIS REASON...AN ENHANCED WIND
   DAMAGE THREAT WILL BE POSSIBLE WITH BOWING LINE-SEGMENTS IN LOWER MI
   LATE THIS AFTERNOON. LARGE HAIL AND A FEW TORNADOES MAY ALSO OCCUR
   WITH THE MORE INTENSE CELLS.
   
   ...NRN APPALACHIAN MTNS...
   AN UPPER-LEVEL RIDGE WILL BE IN PLACE TODAY ACROSS THE APPALACHIAN
   MTNS. IN SPITE OF THE RIDGE...MODERATE INSTABILITY IS FORECAST TO
   DEVELOP FROM PA NEWD ACROSS CNTRL NY WHERE SFC DEWPOINTS SHOULD BE
   IN THE LOWER TO MID 60S F. THE MODELS APPEAR TO MOVE A DISTURBANCE
   OVER THE TOP OF THE RIDGE WHICH WOULD HELP WITH CONVECTIVE
   INITIATION THIS AFTERNOON. IF STORMS CAN DEVELOP IN SPITE OF THE
   WEAK LARGE-SCALE ASCENT...THEN STEEP LOW-LEVEL LAPSE RATES COUPLED
   WITH MODERATE INSTABILITY AND SUFFICIENT DEEP LAYER SHEAR COULD BE
   SUPPORTIVE OF A MARGINAL WIND DAMAGE THREAT.
   
   ..BROYLES/MEAD.. 05/21/2013
   
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