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Turning Stormy in the Northwest

An active fall storm pattern developing in the Pacific Northwest this week will bring areas of heavy rain and high elevation snow. Northern California will benefit from rainfall this week that will aid firefighters given the recent large wildfires. Read More >

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