SWODY1
SPC AC 171630
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CDT MON SEP 17 2007
VALID 171630Z - 181200Z
..THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON INTO
TONIGHT FROM NEB TO MN...
..CENTRAL PLAINS TO UPPER MS VALLEY THIS AFTERNOON INTO TONIGHT...
THE LARGE SCALE PATTERN IS EVOLVING TO A MEAN WRN TROUGH AND A RIDGE
FROM THE SRN PLAINS TO THE OH VALLEY. WITHIN THE BROADER FLOW
REGIME...ONE PRIMARY SHORTWAVE TROUGH OVER UT/NRN AZ WILL LOSE
AMPLITUDE AND EJECT NEWD TOWARD THE CENTRAL PLAINS WHILE ANOTHER
WAVE OVER NRN CA MOVES EWD TOWARD THE FOUR CORNERS BY EARLY TUESDAY.
THIS MORNING/S AZ/UT WAVE WILL BE PRECEDED BY A SERIES OF LOW
AMPLITUDE SPEED MAXIMA EJECTING NEWD FROM NRN CO/WRN NEB OVER SD/NW
MN...AND A SEPARATE SRN STREAM FROM ERN NM TOWARD ERN NEB/WRN IA/SRN
MN BY TONIGHT. AT THE SURFACE...A WARM FRONT IS LIFTING NEWD ACROSS
WI/MN AS A BELT OF MID 60S BOUNDARY LAYER DEWPOINTS SPREADS NEWD ON
A 35-50 KT LLJ. A REMNANT LEE CYCLONE OVER THE CENTRAL DAKOTAS WILL
DRIFT EWD TODAY AS THE MID-UPPER SPEED MAXIMA EJECT NEWD FROM THE
HIGH PLAINS...AND A TRAILING LEE TROUGH WILL BE MAINTAINED FROM E/SE
CO INTO CENTRAL NEB. THIS LEE TROUGH/WEAK CYCLONE WILL DEMARCATE
THE WRN EDGE OF THE MOIST SECTOR...AND PROVIDE THE PRIMARY FOCUS FOR
STRONG/SEVERE STORM DEVELOPMENT LATE TODAY INTO TONIGHT.
REGIONAL 12Z SOUNDINGS SHOW THE POTENTIAL FOR MLCAPE VALUES OF
1500-2000 J/KG THIS AFTERNOON FROM NEB TO MN. HOWEVER...A WARM
ELEVATED MIXED LAYER WILL LIKELY INHIBIT SURFACE-BASED STORM
INITIATION UNTIL LATE THIS AFTERNOON. THE INITIAL STORMS MAY EVOLVE
FROM MID LEVEL CONVECTION ASSOCIATED WITH THE LEAD SPEED MAX NOW
MOVING NEWD FROM WRN NEB...WHILE A SEPARATE CLUSTER OF STORMS MAY
FORM BY TONIGHT OVER KS/NEB WITH THE EJECTING WAVE FROM NM.
MEANWHILE...VERTICAL SHEAR IS FORECAST TO BE AT LEAST MARGINALLY
FAVORABLE FOR ORGANIZED BOWING SEGMENTS/SUPERCELLS ALONG THE
BOUNDARY. THE ORIENTATION OF THE SURFACE BOUNDARY LARGELY PARALLEL
TO THE DEEP LAYER FLOW/SHEAR VECTORS...AND PRIMARILY UNIDIRECTIONAL
WIND PROFILES BY LATE EVENING...SUGGEST THAT CONVECTION MAY TEND TO
EVOLVE INTO AN EXTENSIVE NE-SW BAND BY EARLY TONIGHT FROM CENTRAL MN
SWWD INTO CENTRAL NEB. DAMAGING WINDS AND LARGE HAIL WILL BE THE
MAIN SEVERE THREATS...THOUGH AN ISOLATED TORNADO OR TWO COULD OCCUR
IF DISCRETE STORMS CAN PERSIST IN THE REGION OF STRONGER LOW-LEVEL
SHEAR IN PROXIMITY TO THE NRN EDGE OF THE UNSTABLE WARM SECTOR.
.THOMPSON/GRAMS.. 09/17/2007
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