SPC AC 241951
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0251 PM CDT MON AUG 24 2009
   
   VALID 242000Z - 251200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS ERN ND AND NWRN MN...
   
   ...NRN PLAINS...
   SEVERAL MORE HOURS OF HEATING AND PERSISTENT SYNOPTIC SCALE FORCING
   FOR ASCENT WILL BE NEEDED TO OVERCOME PRONOUNCED CONVECTIVE
   INHIBITION ACROSS THE DAKOTAS AND NRN MN. FORCING NEAR THE SURFACE
   LOW...AND ALONG ADVANCING FRONT...SHOULD THEN BE SUFFICIENT FOR TSTM
   DEVELOPMENT WITHIN MOIST AND MODERATELY UNSTABLE AIRMASS. SHEAR
   ACROSS THE REGION COULD RESULT IN A FEW MORE PERSISTENT STORMS WITH
   POTENTIAL FOR HAIL/WIND. SEE PREVIOUS DISCUSSION FOR ADDITIONAL
   DETAILS.
   
   ...CENTRAL HIGH PLAINS...
   EXPANDED LOW PROBABILITY SEVERE WIND POTENTIAL ACROSS PARTS OF WRN
   KS AND ERN/SERN CO WHERE PERSISTENT HEATING AND LOW LEVEL
   CONVERGENCE MAY PROMOTE HIGH-BASED TSTM DEVELOPMENT WITHIN SURFACE
   TROUGH AXIS NEXT FEW HOURS. NAM-WRF FORECASTS INDICATE A PERSISTENT
   CORRIDOR OF CONVECTION ACROSS THESE AREAS THROUGH LATE EVENING WHERE
   HOT AND DEEPLY MIXED BOUNDARY LAYER COULD SUPPORT ISOLATED DAMAGING
   DOWNBURST WINDS.
   
   ...MID ATLANTIC...
   LOW SEVERE STORM PROBABILITIES HAVE BEEN REMOVED FROM THE
   CAROLINAS/ERN VIRGINIA AREAS FOR THE REMAINDER OF THIS FORECAST
   PERIOD. WHILE CHANCE FOR A COUPLE OF STRONGER STORMS STILL
   EXISTS...LACK OF MORE PRONOUNCED FORCING FOR ASCENT...AND GENERALLY
   WEAKENING DEEP-LAYER FLOW REGIME...SHOULD LIMIT MORE ORGANIZED
   DEVELOPMENT.
   
   ..CARBIN/COOK.. 08/24/2009
   
   .PREV DISCUSSION... /ISSUED 1119 AM CDT MON AUG 24 2009/
   
   ...EXTREME ERN ND/NWRN MN...
   UPPER TROUGH FROM SASKATCHEWAN INTO MT IS FORECAST TO MOVE EWD
   ACROSS THE CANADIAN PRAIRIE PROVINCES AND ND THROUGH THE
   PERIOD...WITH STRONGER MID LEVEL WINDS TRANSLATING ACROSS THE NRN
   BORDER REGION.  SURFACE LOW CURRENTLY OVER CENTRAL ND IS EXPECTED TO
   MOVE ENEWD ACROSS NERN ND/EXTREME NWRN MN LATE THIS AFTERNOON AND
   EVENING...CONTINUING TOWARD CENTRAL ONTARIO TONIGHT.  TRAILING COLD
   FRONT EXTENDING SWWD FROM THE LOW WILL MOVE EWD ACROSS THE NRN
   PLAINS...REACHING A MN ARROWHEAD/SWRN MN/CENTRAL NEB/ERN CO BY
   25/12Z.
   
   MOISTURE IS EXPECTED TO GRADUALLY INCREASE NNEWD ACROSS THE ERN DAKS
   INTO MN AHEAD OF THE ADVANCING COLD FRONT...IN ASSOCIATION WITH A
   30-40 KT LOW LEVEL JET.  SURFACE DEW POINTS ARE EXPECTED TO RISE
   INTO THE MID-UPPER 60S THIS AFTERNOON...BENEATH A LAYER OF STEEP
   LAPSE RATES/ELEVATED MIXED LAYER THAT HAS SPREAD EWD ACROSS THE NRN
   PLAINS INTO THE UPPER MS VALLEY.  WEAK ELEVATED CONVECTION MOVING
   ACROSS ERN ND IS EXPECTED TO DIMINISH THIS AFTERNOON WITH A CAPPING
   INVERSION INHIBITING DEVELOPMENT OF SURFACE-BASED CONVECTION THROUGH
   MUCH OF THE AFTERNOON.
   
   BREAKS IN CLOUD COVER/THINNING OF CLOUDS IS EXPECTED TO SPREAD NEWD
   OVER ERN ND AND NWRN MN AHEAD OF THE COLD FRONT THIS AFTERNOON. THIS
   WILL PERMIT LOCALIZED AREAS OF STRONGER DIABATIC HEATING TO OCCUR
   WHICH WILL GRADUALLY WEAKEN THE CAP.  THIS WILL RESULT IN
   DESTABILIZATION WITH MLCAPE OF 1500-2000 J/KG LATER THIS AFTERNOON
   AND EVENING.  FOCUSED MESOSCALE ASCENT ALONG THE COLD FRONT COUPLED
   WITH DYNAMIC FORCING ALOFT WITHIN THE RIGHT ENTRANCE REGION OF THE
   UPPER LEVEL JET ARE EXPECTED TO BE SUFFICIENT FOR THUNDERSTORMS TO
   DEVELOP LATE THIS AFTERNOON OR EVENING OVER EXTREME ERN ND OR NWRN
   MN.  WIND PROFILES ARE EXPECTED TO VEER AND INCREASE WITH HEIGHT
   WITH RESULTANT 35-45 KT DEEP LAYER SHEAR SUFFICIENT FOR ORGANIZED
   STRONG/SEVERE STORMS TO DEVELOP...INCLUDING POTENTIAL FOR ISOLATED
   SUPERCELLS.  STRONGER CELLS WILL BE CAPABLE OF PRODUCING LARGE HAIL
   AND DAMAGING WIND GUSTS.  ACTIVITY IS LIKELY TO SPREAD EWD DURING
   THE OVERNIGHT HOURS...ALTHOUGH SEVERE POTENTIAL IS EXPECTED TO
   DIMINISH BY 03-6Z AS BOUNDARY LAYER COOLING OCCURS.
   
   ...ERN WY INTO SD AND NEB...
   WATER VAPOR IMAGERY SHOWS A MID/UPPER LEVEL TROUGH LIFTING NEWD FROM
   THE FOUR-CORNERS REGION TOWARD THE CENTRAL ROCKIES...AND MODEL
   GUIDANCE INDICATES THIS TROUGH MOVE INTO THE CENTRAL PLAINS TONIGHT.
   THE DEEP LAYER MOISTURE PLUME AHEAD OF THIS TROUGH OVER THE ROCKIES
   IS EXPECTED TO INTERACT WITH THE COLD FRONT MOVING SWD INTO THE
   CENTRAL HIGH PLAINS LATER THIS AFTERNOON.  LOW LEVEL MOISTURE MAY
   ALSO BE ENHANCED BY INCREASING SURFACE DEW POINTS ALONG/NORTH OF THE
   FRONT.  SCATTERED THUNDERSTORMS ARE EXPECTED TO INCREASE FROM ERN WY
   EWD INTO THE HIGH PLAINS OF WRN NEB AND SWRN SD BY THIS EVENING. 
   STORMS ARE LIKELY TO SPREAD EWD ACROSS PARTS OF NEB AND SD TONIGHT
   AS A SECONDARY LOW LEVEL JET DEVELOPS OVER THE CENTRAL
   PLAINS...ENHANCING CONVERGENCE AND WARM ADVECTION OVER THE AREA. 
   THE CONVECTIVE ACTIVITY WILL BE SOUTH OF THE STRONGER WINDS
   ALOFT...AND GENERALLY MARGINAL SHEAR IS EXPECTED TO LIMIT THE
   OVERALL COVERAGE OF THE SEVERE THREAT.
   
   ...NC/VA...
   THE MAIN UPPER TROUGH AXIS WILL TRACK EASTWARD ACROSS THE MID
   ATLANTIC AND CAROLINAS TODAY.  RELATIVELY COOL TEMPERATURES ALOFT
   /-11C AT 500 MB/ COUPLED WITH BREAKS IN CLOUD COVER/STRONG HEATING
   WILL RESULT IN MLCAPE VALUES OF 1000-1500 J/KG.  SCATTERED
   THUNDERSTORMS ARE EXPECTED TO DEVELOP LATER TODAY FROM EAST TN INTO
   MUCH OF VA/NC.  A FEW STRONG MULTICELL STORMS ARE POSSIBLE WITH A
   RISK OF HAIL AND GUSTY WINDS...BUT WEAK VERTICAL SHEAR SUGGEST THAT
   AN ORGANIZED SEVERE STORM THREAT IS UNLIKELY TO DEVELOP.
   
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