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Day 1 Convective Outlook issued at 0553 UTC 26 August 2008
Click to view the probability of tornadoes, large hail, and damaging wind.
SPC AC 260553
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1253 AM CDT TUE AUG 26 2008
   
   VALID 261200Z - 271200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SOUTHEAST
   STATES/SOUTHERN APPALACHIANS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTHERN/CENTRAL
   PLAINS...
   
   ...SYNOPSIS...
   AN AMPLIFIED/PROGRESSIVE LARGE SCALE FLOW REGIME WILL CONTINUE OVER
   CANADA AND THE NORTHERN HALF OF THE CONUS THROUGH THE PERIOD. BROAD
   UPPER RIDGE WILL SHIFT EASTWARD OVER THE GREAT LAKES REGION/EASTERN
   CANADA...WHILE A POWERFUL UPPER TROUGH/STRONG COLD FRONT TRANSITIONS
   FROM THE NORTHERN GREAT DIVIDE VICINITY TO THE CENTRAL CANADIAN
   PROVINCES/NORTHERN PLAINS. FARTHER SOUTH...REMNANTS OF TROPICAL
   DEPRESSION FAY WILL MIGRATE NORTHEASTWARD ACROSS THE SOUTHEAST
   STATES/TENNESSEE VALLEY THROUGH TONIGHT.
   
   ...SOUTHEAST STATES/SOUTHERN APPALACHIANS...
   REMNANTS OF TROPICAL DEPRESSION FAY WILL CONTINUE TO SPREAD
   NORTHEASTWARD /POTENTIALLY ACCELERATING AND BECOMING MORE
   EXTRATROPICAL WITH TIME/ THROUGH THE DAY. AS HAS BEEN THE CASE OVER
   THE PAST FEW DAYS...STRONG LOW LEVEL FLOW FIELDS/SUFFICIENT SRH FOR
   ISOLATED/BRIEF TORNADOES WILL PERSIST ON THE EASTERN PERIPHERY OF
   RESIDUAL FAY. IT IS IMPORTANT TO NOTE THAT THE 00Z NAM FEATURES A
   RELATIVELY SLOW NORTHEASTWARD TRACK OF FAY REMNANTS...WITH STRONGEST
   LOW LEVEL FLOW FOCUSED ALONG/JUST WEST OF THE APPALACHIANS. IN
   CONTRAST...00Z GFS/12Z ECMWF GUIDANCE REFLECT MORE PROGRESSIVE
   SOLUTIONS AND STRONGER LOW LEVEL FLOW CONSIDERABLY FARTHER EAST
   /ALONG AND EAST OF THE APPALACHIANS/. THE PRIMARY TORNADO RISK
   SHOULD OCCUR DURING THE DAYLIGHT HOURS AS DIABATIC HEATING
   CONTRIBUTES TO SOMEWHAT MORE VIGOROUS UPDRAFTS/SUSTAINED LOW LEVEL
   MESOCYCLONES. WHILE TOTAL INSTABILITY/LAPSE RATES WILL BE WEAK
   ESPECIALLY WITH NORTH EXTENT ACROSS THE SOUTHERN APPALACHIANS
   VICINITY...A SOUTH-SAGGING WEST-EAST FRONTAL BOUNDARY OVER THE
   REGION MAY PROVIDE SOME ADDITIONAL IMPETUS FOR POSSIBLE TORNADOES IN
   ADDITION TO THE INHERENTLY STRONG LOW LEVEL SHEAR/SRH.
   
   ...NORTHERN/CENTRAL PLAINS...
   A STRONG UPPER TROUGH AND ASSOCIATED COLD FRONT WILL STEADILY SPREAD
   EASTWARD ACROSS THE NORTHERN PLAINS TODAY. A STRONG ELEVATED MIXED
   LAYER OVERSPREADING THE REGION SHOULD CAP THE PREFRONTAL WARM SECTOR
   FOR MUCH OF THE DAY. BUT BY LATE AFTERNOON/EARLY EVENING...SCATTERED
   TSTM DEVELOPMENT SHOULD OCCUR NEAR THE FRONT AS INCREASING LARGE
   SCALE FORCING FOR ASCENT AND AMPLE FRONTAL FORCING OVERCOME THE CAP.
   WITH A RELATIVELY NARROW CORRIDOR OF RESIDUAL UPPER 50S/LOWER 60S F
   DEWPOINTS ACROSS THE HIGH PLAINS...THIS DEVELOPMENT WILL INTERCEPT
   AN AXIS OF MODERATE INSTABILITY WITH 1000-2000 J/KG
   MLCAPE...MAXIMIZED ACROSS THE WEST-CENTRAL PORTIONS OF NEB/SD. THE
   STRONGER MID LEVEL FLOW AND ASSOCIATED DEEP LAYER VERTICAL SHEAR
   WILL TEND TO LAG THE SURFACE COLD FRONT. EVEN SO...SOME SUPERCELLS
   WILL BE POSSIBLE WITH THE INITIAL/MORE DISCRETE DEVELOPMENT INTO
   EARLY EVENING. BUT ULTIMATELY THE ARRIVAL OF STRONG FRONTAL FORCING
   SHOULD RESULT IN A RELATIVELY QUICK LINEAR EVOLUTION DURING THE
   EARLY/MID EVENING HOURS. BOTH SEVERE HAIL/WIND WILL BE POSSIBLE. THE
   RELATIVELY LONGEST DURATION SEVERE THREAT DURING THE EVENING /AND
   PERHAPS OVERNIGHT/ SHOULD PERSIST ACROSS NEB/SD...AS TSTMS
   CONGEAL/SPREAD SOUTHEASTWARD SUPPORTED BY AN INCREASINGLY STRONG
   SOUTHERLY LOW LEVEL JET /30-40 KT/ AND ASSOCIATED MOISTURE TRANSPORT
   REGIME/INSTABILITY INFLUX.
   
   ...AZ/FAR SOUTHERN NV/INTERIOR SOUTHERN CA...
   WITH TROPICAL DEPRESSION JULIO ACROSS THE GULF OF CALIFORNIA...A
   VERY MOIST/UNSTABLE AIRMASS WILL REMAIN ACROSS THE SOUTHWEST STATES
   TODAY. WITH SCATTERED TSTM DEVELOPMENT/INTENSIFICATION ANTICIPATED
   THIS AFTERNOON...SOME PULSE-TYPE/ISOLATED SEVERE WIND GUSTS WILL BE
   POSSIBLE WITH THE STRONGEST TSTMS...EVEN WITH A PARTIALLY
   CONVECTIVELY OVERTURNED AIRMASS YESTERDAY.
   
   ..GUYER/JEWELL.. 08/26/2008
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z



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