SWODY1
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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