SPC AC 200606
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0106 AM CDT THU APR 20 2006
   
   VALID 201200Z - 211200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM TX ACROSS THE LOWER MS
   VALLEY TO SRN KY...TN...WRN GA...
   
   ...SYNOPSIS...
   SPRINGTIME CUTOFF LOW ACROSS THE UPPER MS VALLEY WILL MAKE ONLY SLOW
   EWD PROGRESS TOWARD THE WRN GREAT LAKES THIS PERIOD AS A LOWER
   AMPLITUDE AND MORE PROGRESSIVE IMPULSE IN THE SRN BRANCH MOVES EAST
   FROM AZ/NM TO THE ARKLATEX. DOWNSTREAM FROM THE SRN BRANCH
   IMPULSE...A MORE SUBTLE AND POTENTIALLY CONVECTIVELY ENHANCED SHORT
   WAVE DISTURBANCE IS FORECAST TO TRACK EAST FROM THE SRN
   PLAINS...ACROSS THE LOWER MS VALLEY...AND THEN TO THE CNTRL
   APPALACHIANS THROUGH LATE TONIGHT. THE TWO SRN STREAM PERTURBATIONS
   WILL ENHANCE ASCENT ALONG A QUASI-STATIONARY FRONTAL ZONE WHICH WILL
   REMAIN SITUATED WITHIN A VERY WARM AND MOIST AIRMASS FROM TX TO TN.
   
   ...LOWER MS VALLEY/TN VALLEY...
   ONGOING LARGE MCS FROM NRN TX TO AR WILL MOVE EWD FROM THE ARKLATEX
   THROUGH THE MORNING SUSTAINED BY WEAK TO MODEST MOISTURE FLUX AND
   ASCENT OCCURRING ACROSS STALLED DEEP-LAYER FRONTAL ZONE. GUIDANCE
   APPEARS TO SUGGEST THAT A FRONTAL WAVE COINCIDENT WITH THIS COMPLEX
   WILL PROPAGATE ENEWD ALONG THE FRONTAL BOUNDARY ACROSS THE LOWER MS
   VALLEY AND INTO THE TN VALLEY THROUGH THE DAY WITH LARGE SCALE
   ASCENT ACROSS THESE AREAS ENHANCED BY POSSIBLE MCV. RELATIVELY
   UNDISTURBED WARM SECTOR AIR MASS SHOULD EXIST EAST OF THE
   APPROACHING MCS...AND WEST OF RESIDUAL BACK DOOR FRONT/MCS
   OUTFLOW...FROM MIDDLE TN TO NRN MS. EXPECT MODERATELY UNSTABLE
   CONDITIONS TO DEVELOP ALONG THE FRONT IN THIS REGION THROUGH THE
   MORNING GIVEN SUFFICIENT HEATING. FORCING ASSOCIATED WITH THE
   APPROACHING WAVE SHOULD PROMOTE ADDITIONAL SURFACE-BASED TSTM
   DEVELOPMENT FROM NRN MS/WRN TN...EWD ACROSS MIDDLE TN AND NRN AL
   THROUGH THE AFTERNOON. FORECAST SOUNDINGS ACROSS THE REGION APPEAR
   TO INDICATE WEAK EFFECTIVE SHEAR ACROSS THE WARM SECTOR INITIALLY
   WHICH MAY RESULT IN GREATER CONCENTRATION OF MULTICELL STORMS WITH
   SOME HAIL POTENTIAL. HOWEVER...MID LEVEL FLOW AND DEEP SHEAR
   STRENGTHEN DURING THE AFTERNOON SO STORMS MAY BECOME BETTER
   ORGANIZED ALONG THE FRONT AND NEAR SURFACE WAVE. THUS... EXPECT
   ORGANIZED MULTICELLS AND PERHAPS A COUPLE OF SUPERCELLS SPREADING
   EAST ACROSS THE REGION THROUGH THE AFTERNOON. THIS ACTIVITY WILL BE
   CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS. TORNADO
   POTENTIAL MAY ALSO EVOLVE WITH CELLS TRACKING PREFERENTIALLY NEAR
   THE FRONT...AND ACROSS THE RESIDUAL OUTFLOW BOUNDARY WHERE LOW LEVEL
   FLOW WILL BE LOCALLY BACKED AND STRONGER SHEAR WILL LIKELY EXIST.
   
   ANOTHER FOCUS FOR STORM DEVELOPMENT MAY EXIST FROM SRN GA WWD ACROSS
   SRN AL AND MS BY LATE AFTERNOON. A SEGMENT OF RESIDUAL FRONT/OUTFLOW
   MAY MOVE INTO THESE AREAS WHERE DIURNAL HEATING WILL BOOST CAPE BUT
   REGION MAY REMAIN CAPPED UNTIL LATER IN THE DAY. MODEST MID LEVEL
   FLOW WILL PROMOTE ORGANIZED STORMS DEVELOPING IN THIS REGIME WITH
   ATTENDANT THREAT OF HAIL AND WIND. WITH DIURNAL FORCING BEING THE
   PRIMARY FACTOR IN THE DEVELOPMENT OF THIS ACTIVITY...EXPECT SEVERE
   POTENTIAL TO GRADUALLY WANE AFTER SUNSET.
   
   ...WEST TX TO THE ARKLATEX...
   FRONTAL ZONE FROM HILL COUNTRY TO ARKLATEX WILL REMAIN WELL DEFINED
   IN THE WAKE OF OVERNIGHT/MORNING MCS. AIR MASS ALONG AND SOUTH OF
   THE FRONT IS EXPECTED TO BECOME INCREASINGLY UNSTABLE THROUGH THE
   DAY WITH 60S DEWPOINTS AND STEEP MID LEVEL LAPSE RATES CONTRIBUTING
   TO MLCAPE OF 1500-2000 J/KG. HEIGHT FALLS AND LARGE SCALE ASCENT
   WITH APPROACHING SRN BRANCH SHORT WAVE TROUGH SHOULD INDUCE SURFACE
   PRESSURE FALLS ACROSS WRN TX WITH WARM SECTOR POSSIBLY EXPANDING NWD
   AS LOW LEVEL SELY FLOW STRENGTHENS AHEAD OF DEEPENING TRIPLE POINT
   SURFACE WAVE AND SHARPENING DRYLINE.
   
   FORECAST SOUNDINGS ACROSS THE REGION ARE INDICATING 40-45KT
   EFFECTIVE SHEAR NEAR THE FRONT...AND DEVELOPING EWD ACROSS THE WARM
   SECTOR INTO THE EVENING. GIVEN EXPECTED FORCING AND
   INSTABILITY...ENVIRONMENT SHOULD SUPPORT THE DEVELOPMENT OF
   SUPERCELLS CAPABLE OF PRODUCING LARGE...POSSIBLY SIGNIFICANT...
   HAIL. ANY DISCRETE STORMS TRACKING NEAR/ALONG THE WSW-ESE ORIENTED
   FRONTAL BOUNDARY...OR NEAR SURFACE WAVE...COULD ALSO POSE A THREAT
   FOR TORNADOES WHERE LOW-LEVEL SHEAR AND BOUNDARY LAYER RH WILL BE
   MAXIMIZED. STORMS MAY UNDERGO UPSCALE ORGANIZATION INTO AN MCS
   THROUGH THE LATE EVENING AND DAMAGING WIND POTENTIAL MAY INCREASE AS
   THIS MCS SPREADS EAST TOWARD THE GULF COAST THROUGH EARLY FRIDAY.
   
   IT IS POSSIBLE THAT SEVERE WEATHER PROBABILITIES MAY BE
   INCREASED...AND CATEGORICAL OUTLOOK COULD BE UPGRADED...ACROSS
   PORTIONS OF TX AS EVOLUTION OF SEVERE WEATHER SCENARIO BECOMES MORE
   CERTAIN WITH ADDITIONAL SHORT-TERM ANALYSIS AND FORECAST DATA.
   
   ..CARBIN/JEWELL.. 04/20/2006
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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