Aug 13, 2011 1300 UTC Day 1 Convective Outlook
Updated: Sat Aug 13 13:04:12 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20110813 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110813 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
20110813 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
20110813 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.
   SPC AC 131300
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0800 AM CDT SAT AUG 13 2011
   
   VALID 131300Z - 141200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID MS VLY INTO THE
   LWR OH VLY/CNTRL GRT LKS...
   
   ...SYNOPSIS...
   MN/IA SHORTWAVE TROUGH WILL AMPLIFY SE ACROSS THE MID MS/LWR OH VLYS
   THIS PERIOD AS FOUR CORNERS UPR RIDGE IS NUDGED SLIGHTLY E BY BROAD
   TROUGH APPROACHING BC AND THE PACIFIC NW.  IN THE BASE OF THE MN/IA
   TROUGH...SATELLITE SHOWS A WEAK DISTURBANCE NOW OVER NEB THAT SHOULD
   CONTINUE SE ACROSS MO LATER TODAY...AND INTO SRN IL BY EVE.  FARTHER
   S AND E...SATELLITE AND VWP DATA ALSO SUGGEST THE PRESENCE OF
   DISTURBANCES...POSSIBLY CONVECTIVELY ENHANCED...OVER CNTRL
   TX...GA...AND LWR MI.
   
   AT LWR LVLS...LOOSELY ORGANIZED SFC LOW ASSOCIATED WITH MN/IA TROUGH
   SHOULD MOVE GENERALLY ESE INTO LWR MI LATER TODAY/TNGT...AND INTO OH
   EARLY SUN...REMAINING WEAK.  IN ITS WAKE...A DIFFUSE/SEGMENTED COLD
   FRONT WILL SETTLE SE ACROSS PARTS OF THE MID MS VLY...OZARKS...AND
   SRN PLNS THIS AFTN...SERVING AS A FOCUS FOR POSSIBLE STRONG TO SVR
   TSTMS.  AHEAD OF THE FRONT...A SERIES OF OUTFLOW BOUNDARIES AND
   REMNANTS OF A PREVIOUS COOL FRONTAL SURGE WILL FOCUS DIURNALLY
   ENHANCED STORMS FROM CNTRL TX EWD ACROSS THE GULF CST REGION INTO
   THE CAROLINAS.
   
   ...MID MS/LWR OH VLYS TO CNTRL GRT LKS THIS AFTN/EVE...
   SCTD CONVECTION/STORMS LIKELY WILL PERSIST THROUGH MIDDAY FROM PARTS
   OF THE MID MS VLY ENE INTO THE CNTRL GRT LKS...ASSOCIATED WITH MI
   UPR IMPULSE...AND WITH WAA DOWNSTREAM FROM AMPLIFYING MN/IA TROUGH. 
   CONTINUED ENE MOTION OF THE MI DISTURBANCE WILL LEAVE LOW LVL FLOW
   VEERED TO WSWLY ACROSS THE MIDWEST/MID MS VLY.  ALTHOUGH THIS WILL
   MINIMIZE LOW LVL CONVERGENCE...IT ALSO WILL ALLOW LOW LVL MOISTURE
   /SFC DEW POINTS IN THE LOW TO MID 60S F/ TO SPREAD FROM THE CNTRL
   PLNS INTO THE MIDWEST BENEATH MID LVL COOL ADVECTION /500 MB TEMPS
   FALLING TO AOB MINUS 10 C/.  COUPLED WITH WHAT SHOULD BE FAIRLY
   STRONG SFC HEATING...EXPECT 1500-2500 SBCAPE BY AFTN FROM FAR ERN
   MO/IL ENE INTO WRN KY...IND...AND  SRN LWR MI.
   
   LOW LVL DESTABILIZATION AND ASCENT AHEAD OF BOTH MN/IA TROUGH AND
   THE SECONDARY IMPULSE PIVOTING SE ACROSS MO SHOULD LEAD TO THE
   DEVELOPMENT OF SCTD STRONG TO SVR TSTMS ALONG COLD FRONT FROM
   NRN/CNTRL IL AND PERHAPS FAR ERN IA ENE INTO NW IND AND LWR MI BY
   EARLY TO MID AFTN.  WITH REGION IN ZONE OF ASCENT ALONG AND N OF
   40-45 KT WLY MID LVL JET STREAK...SETUP APPEARS FAVORABLE FOR
   SUSTAINED STORMS/SUPERCELLS /SOME OF WHICH MAY ORGANIZE INTO
   BOWS/...WITH SVR WIND AND HAIL.  THE ACTIVITY SHOULD DEVELOP SWWD
   ALONG THE FRONT WITH TIME AS REGION OF LARGE SCALE ASCENT MOVES
   ESEWD.  THIS WILL RESULT IN AN AREAL EXPANSION OF THE SVR THREAT
   INTO THE LWR OH VLY BY LATE IT THE DAY AND THIS EVE...WITH A
   CONTINUED THREAT FOR DMGG WIND.  FARTHER N...WEAKER DEEP SHEAR BUT
   COMPARATIVELY BACKED LOW LVL FLOW IN THE PRESENCE OF MODERATE
   BOUNDARY LAYER RH MAY YIELD A BRIEF TORNADO NEAR WARM FRONT THIS
   AFTN IN CNTRL LWR MI.
   
   ...SRN STATES THIS AFTN...
   A MODEST INCREASE IN NWLY MID/UPR LVL FLOW WILL OCCUR FROM THE SRN
   PLNS INTO THE LWR MS AND TN VLYS TODAY...ON SRN FRINGE OF
   MIDWESTERN TROUGH.  LOCAL SPEED MAXIMA MAY ACCOMPANY AFOREMENTIONED
   WEAK DISTURBANCES OVER THE REGION.  IT APPEARS THAT THE STRONGEST
   SFC HEATING WILL OCCUR OVER PARTS OF CNTRL/E TX EWD INTO NRN
   LA...MS...AL AND TN.  STORMS SHOULD REDEVELOP/STRENGTHEN ALONG
   EXISTING OUTFLOW BOUNDARIES AND MOVE/ DEVELOP GENERALLY ESE.  WHILE
   A FEW STORMS MAY POSE A DMGG WIND THREAT...MODEST WIND FIELD AND
   RELATIVELY WEAK MID LVL LAPSE RATES /ABSENCE OF IDENTIFIABLE EML
   REMNANTS/ SUGGEST THAT ANY SUCH THREAT SHOULD REMAIN ISOLD.
   
   ...NC NWD INTO CNTRL PA/NY...
   MI UPR IMPULSE AND ITS SRN EXTENSION WILL MOVE ENE ACROSS THE UPR OH
   VLY/CNTRL-NRN APPALACHIANS THIS AFTN.  AHEAD OF IT...PW VALUES OF
   1.50-1.75 INCHES WILL SPREAD N ALONG THE MOUNTAINS/CSTL PLN.  SCTD
   TO NUMEROUS STORMS SHOULD FORM OVER THE HIGHER TERRAIN FROM NC TO
   SRN NY.  A FEW STORMS MAY BRIEFLY ORGANIZE AND YIELD ISOLD DMGG WIND
   GUSTS AS WLY DEEP SHEAR INCREASES TO 30-35 KTS...PARTICULARLY IN THE
   MID ATLANTIC REGION.  THE STORMS SHOULD REACH THE CSTL PLN BY
   EVE...WITH PERHAPS A LINGERING THREAT FOR GUSTY WIND.
   
   ..CORFIDI/GRAMS.. 08/13/2011
   
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