SPC AC 210540

   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1240 AM CDT TUE APR 21 2015

   VALID 221200Z - 231200Z

   ...THERE IS AN ENH RISK OF SVR TSTMS ACROSS PARTS OF SRN OK AND
   NORTH TO NORTHEAST TX...

   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF OK...SW
   AR...TX...LA AND MS...

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
   PLAINS...ARKLATEX...LOWER MS VALLEY AND CNTRL GULF COAST STATES...

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF SOUTH FL...

   ...SUMMARY...
   THUNDERSTORMS WITH WIND DAMAGE...LARGE HAIL AND POSSIBLY A FEW
   TORNADOES ARE EXPECTED TO DEVELOP FROM THE SOUTHERN PLAINS
   SOUTHEASTWARD ACROSS THE ARKLATEX AND INTO THE LOWER MISSISSIPPI
   VALLEY. OTHER STORMS WITH HAIL AND WIND DAMAGE MAY DEVELOP IN
   CENTRAL TEXAS AND THE TEXAS COASTAL PLAINS. MARGINALLY SEVERE
   THUNDERSTORMS MAY DEVELOP ACROSS PARTS OF THE SOUTHERN HIGH PLAINS
   AND IN SOUTH TEXAS. THUNDERSTORM DEVELOPMENT MAY ALSO OCCUR ACROSS
   PARTS OF THE CENTRAL TO NORTHERN ROCKIES AND SIERRA NEVADA.

   ...SRN PLAINS/ARKLATEX/LOWER MS VALLEY...
   AN UPPER-LEVEL RIDGE IS FORECAST TO BUILD NNWWD ACROSS THE SRN HIGH
   PLAINS INTO THE CNTRL ROCKIES ON WEDNESDAY. AT THE SFC...A LOW IS
   FORECAST TO DEEPEN IN NE NM WITH A WARM FRONT EXTENDING EWD ACROSS
   SCNTRL OK INTO CNTRL AR. SOUTH OF THE BOUNDARY...SFC DEWPOINTS
   SHOULD BE IN THE LOWER TO MID 60S F ACROSS NORTH TX AND SRN OK WHERE
   MODERATE INSTABILITY SHOULD BE IN PLACE BY AFTERNOON. CONVECTION
   APPEARS LIKELY TO INITIATE BY LATE AFTERNOON ALONG THE WARM FRONT IN
   SW OK WITH AN MCS ORGANIZING AND MOVING ESEWD ACROSS SRN OK INTO NE
   TX. THERE IS STILL SOME QUESTION ABOUT TIMING BUT THE GFS SOLUTION
   SEEMS TO BE REASONABLE WITH A LATE AFTERNOON AND EARLY EVENING MCS.

   NAM FORECAST SOUNDINGS FOR 00Z/THU AT FREDERICK OK AND VERNON TX
   SHOW 1500 TO 2000 J/KG OF MLCAPE WITH VERY STEEP MID-LEVEL LAPSE
   RATES APPROACHING 9.0 C/KM. IN ADDITION...AN IMPRESSIVE WIND-SHEAR
   ENVIRONMENT IS FORECAST WITH SUBSTANTIAL VEERING WITH HEIGHT BELOW
   850 AND 0-6 KM SHEAR NEAR 60 KT. THIS WOULD FAVOR THE DEVELOPMENT OF
   SUPERCELLS WITH LARGE HAIL AND WIND DAMAGE EARLY IN THE EVENT.
   HAILSTONES OF GREATER THAN 2 INCHES IN DIAMETER WILL BE POSSIBLE
   WITH THE MORE DOMINANT CELLS. A FEW TORNADOES MAY OCCUR ESPECIALLY
   WITH PERSISTENT ROTATING STORMS. A RELATIVELY FAST-MOVING MCS MAY
   DEVELOP A LINEAR STRUCTURE AND COLD POOL EARLY WEDNESDAY EVENING
   WHICH COULD RESULT IN AN ENHANCED WIND-DAMAGE THREAT. THE SEVERE
   THREAT FROM THIS CONVECTIVE SYSTEM COULD EXTEND AS FAR SOUTHEAST AS
   EAST TX AND NW LA DURING THE EVENING AND POSSIBLY DURING THE EARLY
   OVERNIGHT OVER PARTS OF THE LOWER MS VALLEY.

   ...TX HILL COUNTRY/TX COASTAL PLAINS...
   AN UPPER-LEVEL RIDGE IS FORECAST TO BE MAINTAINED ACROSS THE TX HILL
   COUNTRY AND SRN HIGH PLAINS ON WEDNESDAY AS A WARM SECTOR REMAINS
   LOCATED OVER MUCH OF THE SRN TWO-THIRDS OF TX. THE AIRMASS ACROSS
   THE TX HILL COUNTRY AND THE TX COASTAL PLAINS...AWAY FROM THE
   IMMEDIATE COAST...IS FORECAST TO BECOME MODERATELY TO STRONGLY
   UNSTABLE BY WEDNESDAY AFTERNOON. FORECAST SOUNDINGS FOR 00Z/THU AT
   AUSTIN AND COLLEGE STATION SHOW MLCAPE ABOVE 3000 J/KG WITH LOWER
   70S F DEWPOINTS. IN ADDITION TO THE IMPRESSIVE
   THERMODYNAMICS...DEEP-LAYER SHEAR SHOULD BE IN THE 50 TO 60 KT
   RANGE. THIS SHOULD SUPPORT SEVERE THUNDERSTORM DEVELOPMENT WITH
   SUPERCELLS THE FAVORED STORM MODE. CONVECTIVE COVERAGE IS THE MAIN
   UNCERTAINTY WITH THE UPPER-LEVEL RIDGE TO THE WEST. EVEN THOUGH
   STORM DEVELOPMENT SHOULD REMAIN ISOLATED...SUPERCELLS SHOULD BE
   CAPABLE OF PRODUCING LARGE HAIL...WIND DAMAGE AND POSSIBLY A
   TORNADO.

   ...SRN FL...
   AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE SLOWLY EWD ACROSS THE EAST
   COAST AS A BELT OF STRONGER MID-LEVEL FLOW MOVES EWD ACROSS THE NRN
   GULF OF MEXICO. A MOIST AIRMASS IS FORECAST ACROSS SOUTH FL WHERE
   MODERATE INSTABILITY SHOULD DEVELOP BY MIDDAY. CELLS THAT CAN
   INITIATE ACROSS SOUTH FL DURING THE EARLY AFTERNOON MAY OBTAIN A
   MARGINAL WIND DAMAGE THREAT DUE TO MODERATE DEEP-LAYER SHEAR AND
   UNIDIRECTIONAL WIND PROFILES.

   ..BROYLES.. 04/21/2015

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