Mike Wilhelm's Alabama Weather Blog

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Bamawx.com

DAY 2 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
1235 AM CDT FRI APR 23 2010  
 
VALID 241200Z - 251200Z 
  
...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF SWRN AND S-CNTRL  
KY...WRN AND MIDDLE TN...ERN AR...NWRN LA...MUCH OF MS...WRN AND NRN  
AL AND FAR NWRN GA...  
  
...THERE IS A SLGT RISK OF SVR TSTMS FROM LOWER ELEVATIONS OF THE  
CNTRL AND SRN PLAINS EWD TO THE CNTRL/SRN APPALACHIANS AND ERN GULF  
STATES...  
  
..SYNOPSIS  
  
A DYNAMIC LARGE-SCALE PATTERN WILL CONTINUE THROUGH THE DAY TWO  
PERIOD FEATURING A DEEP-LAYER CYCLONE WHICH WILL TRACK FROM THE  
CNTRL PLAINS ENEWD THROUGH THE MID MS VALLEY BEFORE RE-DEVELOPING  
INTO IL/IND BY SUNDAY MORNING.  OF POTENTIALLY MORE SIGNIFICANCE IS  
A VIGOROUS VORTICITY MAXIMUM AND ATTENDANT 80+ KT MIDLEVEL JET  
STREAK WHICH ARE FORECAST TO ROUND THE LARGE-SCALE TROUGH BASE OVER  
TX PRIOR TO ACCELERATING NEWD --AS A NEGATIVELY-TILTED WAVE--  
THROUGH THE ARKLATEX/LOWER MS VALLEY AND EVENTUALLY INTO THE OH  
VALLEY.  
  
AT THE SURFACE...A CYCLONE ASSOCIATED WITH THE PRIMARY UPPER-LEVEL  
LOW WILL DEVELOP SLOWLY EWD FROM THE MID MO VALLEY PRIOR TO  
WEAKENING OVER IA.  AN ASSOCIATED COLD FRONT WILL PUSH SEWD THROUGH  
THE MID MO VALLEY AND CNTRL PLAINS...EVENTUALLY INTO THE MID MS  
VALLEY.  MEANWHILE...A SECONDARY CYCLOGENETIC LOW WILL DEVELOP  
RAPIDLY NEWD FROM THE VICINITY OF THE ARKLATEX TO NEAR PAH BY MID  
AFTERNOON AND INTO NRN IND BY THE END OF THE PERIOD.  A COLD OR  
PACIFIC FRONT ASSOCIATED WITH THIS LOW WILL SWEEP EWD THROUGH THE  
MID/LOWER MS VALLEYS AND MUCH OF THE OH VALLEY SATURDAY INTO  
SATURDAY NIGHT.    
  
--TORNADO OUTBREAK POSSIBLE OVER PARTS OF THE LOWER MS AND TN  
VALLEYS INTO CNTRL GULF STATES SATURDAY INTO SATURDAY NIGHT--  
  
...THE LOWER OH/LOWER MS VALLEYS EWD INTO THE CNTRL/SRN APPALACHIANS  
INTO THE ERN GULF STATES...  
  
THE PRESENCE OF A BROAD...MOIST WARM SECTOR /I.E. BOUNDARY LAYER DEW  
POINTS RANGING FROM AROUND 60 F NEAR THE OH RIVER...TO UPPER 60S TO  
AROUND 70 F OVER THE LOWER MS VALLEY AND CNTRL GULF STATES/ WILL SET  
THE STAGE FOR A SIGNIFICANT...AND WIDESPREAD OUTBREAK OF SEVERE  
THUNDERSTORMS THROUGH MUCH OF THE DAY TWO PERIOD.  THIS MOISTURE IN  
CONJUNCTION WITH RELATIVELY STEEP MIDLEVEL LAPSE RATES AND DAYTIME  
HEATING WILL CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS BY  
AFTERNOON OVER THE LOWER MS VALLEY WHERE MLCAPE WILL APPROACH  
1500-2000 J/KG.  WHILE CONVECTIVE INSTABILITY WILL LIKELY DECREASE  
WITH NWD EXTENT OWING TO MORE WIDESPREAD CLOUDS AND PERSISTENT  
CONVECTIVE PRECIPITATION...IT WILL STILL BE SUFFICIENT TO SUPPORT  
SEVERE STORMS.  
  
CLUSTERS OF SEVERE TSTMS ARE FORECAST TO BE ONGOING SATURDAY MORNING  
FROM THE VICINITY OF THE COLD FRONT OVER ERN TX EWD INTO THE LOWER  
MS VALLEY.  ACTIVITY WILL SPREAD NWD/NEWD THROUGH THE PERIOD IN  
ADVANCE OF THE NEGATIVELY-TILTED MIDLEVEL TROUGH RAPIDLY LIFTING  
NEWD THROUGH THE LOWER/MID MS VALLEYS.  THE COMBINATION OF A 60-90  
KT MIDLEVEL WIND FIELD AND A DEVELOPING 50-60 KT LLJ WILL RESULT IN  
STRONG VERTICAL SHEAR ACROSS THE WARM SECTOR.  THIS SUGGESTS A HIGH  
LIKELIHOOD OF MULTIPLE BANDS/CLUSTERS OF SUPERCELLS CAPABLE OF  
DAMAGING WINDS...LARGE HAIL AND TORNADOES PERSISTING THROUGH THE  
PERIOD.   
  
THE GREATEST THREAT FOR CYCLIC SUPERCELLS CAPABLE OF SIGNIFICANT  
TORNADOES WILL EXIST FROM THE VICINITY OF THE SECONDARY LOW TRACK  
SEWD INTO THE WARM SECTOR /I.E. LARGELY DELINEATED BY MDT RISK  
AREA/.  HERE...ENVIRONMENT WILL BE CHARACTERIZED BY DEEP EFFECTIVE  
INFLOW LAYERS YIELDING EFFECTIVE SRH IN EXCESS OF 200-300+  
M2/S2...MODERATE INSTABILITY AND 50-70 KT OF DEEP-LAYER SHEAR.   
SEVERE STORMS CAPABLE OF MAINLY DAMAGING WINDS AND TORNADOES WILL  
CONTINUE THROUGH THE NIGHT WITH THE THREAT EXTENDING NWD THROUGH THE  
OH RIVER AND AS FAR E AS THE CNTRL/SRN APPALACHIANS AND ERN GULF  
STATES.  
  
..MID/LOWER MO VALLEYS INTO THE MID MS VALLEY  
  
A SECONDARY CONCENTRATION OF STRONG TO SEVERE STORMS IS EXPECTED TO  
DEVELOP DURING THE AFTERNOON ALONG AND AHEAD OF THE SECONDARY COLD  
FRONT AND INVOF THE DEEP-LAYER CYCLONE SLOWLY SHIFTING ENEWD.  HERE  
RESIDUAL BOUNDARY LAYER DEW POINTS IN THE MID 40S TO MID 50S COUPLED  
WITH DAYTIME HEATING AND COLD MIDLEVEL TEMPERATURES /I.E. -20 C AT  
500 MB/ WILL YIELD POCKETS OF MODERATE INSTABILITY WHERE MLCAPE WILL  
APPROACH 1000-1500 J/KG.  
  
REGION WILL RESIDE ON THE INNER ENVELOPE OF STRONGER DEEP-LAYER  
SHEAR ASSOCIATED WITH THE SYNOPTIC SYSTEM.  AS SUCH...SETUP WILL BE  
FAVORABLE FOR ORGANIZED MULTICELL OR SUPERCELL STRUCTURES CAPABLE OF  
MAINLY SEVERE HAIL.  ISOLATED TORNADOES WILL ALSO BE POSSIBLE NEAR  
THE SURFACE LOW WHERE AMBIENT...VERTICAL VORTICITY WILL BE  
MAXIMIZED.  
  
..MEAD.. 04/23/2010