Aug 18, 2009 1630 UTC Day 1 Convective Outlook
Updated: Tue Aug 18 16:35:17 UTC 2009
Probabilistic to Categorical Outlook Conversion Table (Effective Feb 14, 2006).
Categorical Graphic
20090818 1630 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20090818 1630 UTC Day 1 Tornado Probabilities Graphic
Torndao Legend Image
Probabilistic Damaging Wind Graphic
20090818 1630 UTC Day 1 Damaging Wind Probabilities Graphic
Wind Legend Image
Probabilistic Large Hail Graphic
20090818 1630 UTC Day 1 Large Hail Probabilities Graphic
Hail Legend Image
   SPC AC 181630
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1130 AM CDT TUE AUG 18 2009
   
   VALID 181630Z - 191200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT FOR
   PARTS OF THE CENTRAL AND SRN HIGH PLAINS...
   
   ...SYNOPSIS...
   THE PREVIOUSLY CLOSED LOW OVER ONTARIO WILL EJECT NEWD AS AN OPEN
   WAVE AS AN UPSTREAM TROUGH OVER CENTRAL AB DIGS SEWD TOWARD THE NRN
   HIGH PLAINS BY THE END OF THE PERIOD.  A SEPARATE...SMALLER SCALE
   TROUGH NOW OVER NE UT/NW CO WILL ALSO PROGRESS EWD OVER CO THROUGH
   THIS EVENING...AND REACH WRN KS OVERNIGHT IN ADVANCE OF THE DIGGING
   TROUGH FROM AB.
   
   ...E/SE CO AND NE NM THIS AFTERNOON TO NW OK OVERNIGHT...
   THE REMNANTS OF OVERNIGHT CONVECTION PERSIST OVER OK TO THE N OF A
   PRONOUNCED OUTFLOW BOUNDARY THAT HAS MOVED SEWD INTO SE OK AND N TX.
    REGIONAL 12Z SOUNDINGS FROM DDC/AMA/OUN CONFIRM THE REDUCTION IN
   LAPSE RATES EXPECTED FROM SUCH WIDESPREAD CONVECTIVE OVERTURNING...
   AND THE RESIDUAL CLOUDS/RAIN-COOLED AIR MASS WILL LIMIT POTENTIAL
   INSTABILITY THIS AFTERNOON ACROSS MUCH OF SRN KS AND OK.  FARTHER
   W...STEEPER MID LEVEL LAPSE RATES PERSIST IN PROXIMITY TO THE HIGHER
   TERRAIN...AND BOUNDARY LAYER DEWPOINTS IN THE LOW-MID 50S HAVE
   SPREAD WWD/NWWD TO THE FRONT RANGE IN CO/NE NM.  AS THE MORNING
   STRATUS CLOUDS ERODE AND TEMPERATURES WARM INTO THE 70S...AFTERNOON
   MLCAPE VALUES WILL INCREASE TO 1000-2000 J/KG.
   
   THUNDERSTORM DEVELOPMENT IS EXPECTED BY MID-LATE AFTERNOON
   IMMEDIATELY E OF THE MOUNTAINS FROM NE NM INTO SE CO AS CONVECTIVE
   INHIBITION IS REMOVED BY SURFACE HEATING/MIXING...AND AS THE BELT OF
   ASCENT DOWNSTREAM FROM THE UT/WRN CO MID LEVEL TROUGH REACHES ERN
   CO.  THE MODERATE INSTABILITY WILL COMBINE WITH EFFECTIVE BULK SHEAR
   OF 40-50 KT TO SUPPORT SUPERCELLS WITH THE POTENTIAL TO PRODUCE
   ISOLATED VERY LARGE HAIL AND DAMAGING WINDS.  LOW-LEVEL SHEAR AND
   BOUNDARY LAYER MOISTURE MAY ALSO BE SUFFICIENT FOR A TORNADO OR TWO
   THIS EVENING IN THE SE CO AREA.  OVERNIGHT... CONVECTION IS EXPECTED
   TO EVOLVE INTO ANOTHER MCS THAT WILL MOVE EWD/ESEWD ACROSS SW
   KS...THE OK AND NRN TX PANHANDLES...AND NW OK LATE IN THE PERIOD. 
   THE THREAT FOR AT LEAST ISOLATED DAMAGING WINDS AND LARGE HAIL WILL
   REACH AS FAR E AS NW OK.
   
   ...NEB/SD AREA THIS AFTERNOON INTO TONIGHT...
   A WEAK LEE TROUGH WILL DEVELOP EWD INTO WRN NEB AND THE WRN DAKOTAS
   THIS AFTERNOON /DOWNSTREAM FROM THE AMPLIFYING NRN STREAM TROUGH/. 
   A GRADUAL INCREASE IN LOW-LEVEL MOISTURE IS EXPECTED E OF THE TROUGH
   ACROSS NEB/SD...WHERE SURFACE HEATING WILL RESULT IN THE DEVELOPMENT
   OF WEAK-MODERATE INSTABILITY BY MID-LATE AFTERNOON.  A FEW
   THUNDERSTORMS COULD FORM ALONG THE BOUNDARY BY LATE AFTERNOON...AND
   THE STRONGEST STORMS MAY PRODUCE MARGINALLY SEVERE HAIL AND ISOLATED
   DAMAGING WINDS.  SOME OF THIS CONVECTION MAY ALSO PERSIST INTO
   TONIGHT AND SPREAD EWD INTO ERN SD AND ADJACENT AREAS IN CONJUNCTION
   WITH LOW-LEVEL WAA AND WEAK ASCENT IN ADVANCE OF THE NRN PLAINS MID
   LEVEL TROUGH.
   
   ...WRN PA/NY THIS AFTERNOON...
   A BROKEN BAND OF PRE-FRONTAL CONVECTION IS EXPECTED THIS AFTERNOON
   FROM ERN OH/WRN PA NEWD INTO WRN NY.  ROUGHLY 30 KT LOW-LEVEL FLOW
   WILL SUPPORT A MARGINAL DAMAGING WIND THREAT WITH THESE STORMS...BUT
   WEAK INSTABILITY/POOR LAPSE RATES WILL LIMIT THE OVERALL THREAT.
   
   ..THOMPSON/GARNER.. 08/18/2009
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z