Mar 18, 2013 1300 UTC Day 1 Convective Outlook
Updated: Mon Mar 18 12:56:35 UTC 2013
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20130318 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20130318 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
20130318 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
20130318 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 180,584 19,399,677 Nashville, TN...Atlanta, GA...Birmingham, AL...Montgomery, AL...Mobile, AL...
   SPC AC 181252
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0752 AM CDT MON MAR 18 2013
   
   VALID 181300Z - 191200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS LA/AR TO ERN KY AND
   CENTRAL GA...
   
   ...SYNOPSIS...
   MID-UPPER LEVEL PATTERN OVER CONUS IS CHARACTERIZED BY BROAD BELT OF
   CYCLONIC FLOW W OF APPALACHIANS...CONTAINING NUMEROUS MAINLY
   LOW-AMPLITUDE PERTURBATIONS.  STRONGEST SHORTWAVE APPEARS OVER
   PORTIONS SD...CENTRAL NEB AND NRN KS...FCST TO MOVE ENEWD AND EVOLVE
   INTO WEAK 500-MB LOW OVER LS BY END OF PERIOD.  PAIR OF
   LOW-AMPLITUDE SHORTWAVE TROUGHS IS EVIDENT IN SATELLITE IMAGERY AND
   RAOB/VWP/PROFILER DATA.  FIRST EXTENDS FROM CENTRAL OZARKS SWWD
   ACROSS W-CENTRAL AR TO TXK AREA.  THAT ONE IS TRAILED CLOSELY BY
   PERTURBATION OVER WRN/CENTRAL OK...WHICH MAY BE SRN EXTENSION OF
   AFOREMENTIONED CENTRAL/NRN PLAINS PERTURBATION.  WEAK/SRN-STREAM
   TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER S-CENTRAL TX
   -- APPEARS TO BE PHASED WITH WRN MEMBER OF OK/AR SHORTWAVE
   PAIR...BUT LIKELY IS DISTINCT VORTICITY LOBE THAT SHOULD MOVE EWD TO
   SRN AL BY 00Z.  
   
   AT SFC...MAIN CYCLONE ASSOCIATED WITH NRN-STREAM TROUGH WAS ANALYZED
   AT 18/11Z BETWEEN FAR-HCO...AND IS EXPECTED TO SHIFT/REDEVELOP EWD
   ACROSS LS THROUGH PERIOD.  OCCLUDED FRONT WAS DRAWN FROM THERE SEWD
   TO BROAD/WEAK CYCLONE ANALYZED BETWEEN PAH-EVV.  COLD FRONT EXTENDED
   SWWD ACROSS ERN THROUGH AR...THEN ARCHING WWD TO NWWD ACROSS NE TX
   AND EXTREME N-CENTRAL TX TO SECONDARY FRONTAL-WAVE LOW BETWEEN
   FTW-SPS.  FRONT WAS ANALYZED FROM THAT LOW WSWWD ACROSS W-CENTRAL TX
   WITH REINFORCING COLD SURGE APPARENT OVER TX PANHANDLE/S-PLAINS
   REGION.  BY 19/00Z...COLD FRONT SHOULD REACH CENTRAL OH...ERN
   KY...NERN MS...W-CENTRAL LA...AND UPPER TX COASTAL PLAIN.  ATLC LOW
   DEVELOPMENT IS PROGGED BY END OF PERIOD S OF LONG ISLAND...WITH COLD
   FRONT SWWD OVER ERN NC...SWRN GA...WRN FL PANHANDLE...AND N-CENTRAL
   GULF. 
   
   ...PORTIONS LA/AR TO ERN KY AND CENTRAL GA...
   OUTLOOK REPRESENTS OVERLAID CUMULATIVE POTENTIAL FROM MULTIPLE AREAS
   OF TSTMS THAT ARE POSSIBLE ACROSS OUTLOOK AREA THROUGH PERIOD. 
   THESE INCLUDE BUT NOT LIMITED TO
   
   1. EWD SHIFT OF NEAR-FRONTAL CONVECTIVE BAND NOW EXTENDING FROM ERN
   KY TO NWRN MS...SRN PORTION OF WHICH IS EXPERIENCING BOTH FRONTAL
   ASCENT AND LAPSE-RATE ENHANCEMENT ALOFT FROM LEADING MEMBER OF OK/AR
   SHORTWAVE PAIR.  THESE TSTMS ARE INITIALLY SUPPORTED BY ELEVATED
   EFFECTIVE-INFLOW PARCELS.  HOWEVER...SOME PORTIONS OF EITHER
   EXISTING ACTIVITY OR NEW DEVELOPMENT IN SAME UVV PLUME MAY BECOME
   SFC-BASED MIDDAY INTO AFTN AS FOREGOING SFC WARM SECTOR BECOMES AT
   LEAST MRGLLY UNSTABLE.  DAMAGING GUSTS AND OCNL HAIL ARE MAIN
   CONCERNS...THOUGH DEEP-LAYER SHEAR MAY SUPPORT BRIEF/CONDITIONAL
   TORNADO POTENTIAL FROM EITHER EMBEDDED SUPERCELLS OR QLCS
   CIRCULATIONS. 
   
   2. EWD MOVEMENT OF INCREASINGLY CONVECTIVE UVV PLUME NOW OVER SERN
   OK...AHEAD OF WRN/CENTRAL OK SECONDARY SHORTWAVE TROUGH.  THIS
   FEATURE IS FCST TO STRENGTHEN AS IT ENCOUNTERS MORE MOIST/UNSTABLE
   INFLOW AIR AT PROGRESSIVELY LOWER HEIGHTS AGL OVER AR AND MS. 
   INITIALLY ELEVATED WITH GROWING HAIL RISK...THESE TSTMS MAY BECOME
   SFC-BASED UPON PASSING OVER FRONTAL ZONE IN SEVERAL HOURS...LEADING
   TO INCREASING GUST THREAT AND AT LEAST BRIEF/MRGL TORNADO RISK AS
   WELL...AMIDST FAVORABLE DEEP SHEAR. REF SPC MESOSCALE DISCUSSION 274
   FOR MORE NEAR-TERM INSIGHTS ON THIS ACTIVITY AND RELATED POTENTIAL
   FOR WW LATER THIS MORNING. 
   
   3. PREFRONTAL CONVECTION OVER PORTIONS ERN MS...AL/GA AND FL
   PANHANDLE MAY BE SUPPORTED BY LARGE-SCALE ASCENT/DESTABILIZATION
   ALOFT OCCURRING AHEAD OF SRN-MOST PERTURBATION NOW OVER TX. 
   BOUNDARY-LAYER AIR MASS OVER THIS REGION SHOULD EXPERIENCE
   RELATIVELY LONG DURATION OF DESTABILIZATION TODAY...RELATED TO
     A. SUSTAINED LOW-LEVEL THETAE ADVECTION AND MOISTURE TRANSPORT
   FROM NEARBY GULF...AND
     B. DIABATIC SFC HEATING...WHICH WILL OCCUR IN PATCHY/TRANSIENT
   FASHION THANKS TO BKN CLOUD COVER. 
   
   EACH SHOULD CONTRIBUTE TO MLCAPE 1500-2000 J/KG THIS
   AFTERNOON...AMIDST 40-50 KT EFFECTIVE SHEAR MAGNITUDES FAVORING
   DEVELOPMENT OF A FEW SUPERCELLS WITH LARGE/POTENTIALLY SIGNIFICANT
   HAIL.  THOUGH RATHER WEAK AT 5-15 KT...RELATIVELY BACKED SFC FLOW
   OVER PORTIONS ERN AL/WRN GA ALSO SHOULD ENHANCE LOW-LEVEL HODOGRAPHS
   AMIDST 35-45 KT SWLY LLJ...LEADING TO EFFECTIVE SRH 250-400 J/KG IN
   PARTS OF THAT REGION.  ANY RELATIVELY DISCRETE CONVECTION IN LATTER
   ENVIRONMENT WILL POSE SUPERCELL/TORNADO THREAT AS WELL. 
   
   4. ISOLATED TO WIDELY SCATTERED TSTMS THIS AFTN OVER PORTIONS LA AND
   WRN MS.  ENVIRONMENT SHOULD BE CHARACTERIZED BY STEEP MIDLEVEL LAPSE
   RATES AND MLCAPE 2000-2500 J/KG.  DESPITE RELATIVELY VEERED
   PREFRONTAL SFC FLOW...ENOUGH DEEP SHEAR IS FCST FOR
   SUPERCELLS...POTENTIALLY SPLITTING STORMS.  WEAKER LOW-LEVEL
   CONVERGENCE AND MORE PRONOUNCED EML/CAPPING OVER THIS AREA RENDERS
   CONSIDERABLE UNCERTAINTY REGARDING CONVECTIVE COVERAGE...BUT
   CONDITIONAL SUPERCELL THREAT IS EVIDENT AS FAR W AS CENTRAL/ERN LA. 
   AS SUCH...HAVE EXTENDED THE CATEGORICAL/15% HAIL RISK INTO THIS
   REGION. 
   
   ...NRN/ERN GA...CAROLINAS...
   CONVECTION MAY EVOLVE INTO QUASI-LINEAR SYSTEM AND MOVE EWD ACROSS
   PARTS OF THIS REGION THIS EVENING AND OVERNIGHT.  ANY SUCH ACTIVITY
   SHOULD BE MOVING EWD INTO PROGRESSIVELY MORE STABLE AIR MASS WITH
   TIME...BUT MAY OFFER THREAT OF AT LEAST ISOLATED DAMAGING GUSTS AND
   MRGL HAIL.  PORTIONS OF THIS AREA MAY REQUIRE LARGER PROBABILITIES
   ONCE CONDITIONAL MODAL/DESTABILIZATION TRENDS THAT ARE NOW
   UNCERTAINTIES BECOME BETTER APPARENT.
   
   ..EDWARDS/ROGERS.. 03/18/2013
   
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