SWODY1
SPC AC 060605
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0105 AM CDT THU SEP 06 2007
VALID 061200Z - 071200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE PLAINS AND PARTS OF
THE UPPER MS VALLEY...
..SYNOPSIS...
PROGRESSIVE UPPER TROUGH NOW MOVING EAST ACROSS THE ROCKIES IS
FORECAST TO ACCELERATE ENEWD FROM THE NRN/CNTRL PLAINS TO THE UPPER
MS VALLEY THROUGH LATE TONIGHT. LARGE SCALE ASCENT ASSOCIATED WITH
THE TROUGH WILL INDUCE SURFACE CYCLOGENESIS ALONG A QUASISTATIONARY
FRONTAL ZONE ORIENTED SW-NE ACROSS THE MID MISSOURI RIVER VALLEY.
CONSOLIDATING LOW PRESSURE CENTER WILL TRACK ALONG THE BOUNDARY FROM
ERN SD/NEB TO MN/WRN LS AREA THROUGH EARLY FRI AS TRAILING COLD
FRONT SWEEPS SWD/SEWD ACROSS THE CNTRL PLAINS.
FARTHER SOUTH...REMAINS OF T.S. HENRIETTE COULD PRODUCE SIGNIFICANT
RAINFALL ACROSS AREAS OF THE SOUTHWEST AS RESIDUAL TROPICAL VORTEX
IS GRADUALLY ABSORBED INTO STRONGER WLYS ON THE FRINGE OF PLAINS
UPPER TROUGH. MEANWHILE...FORMER TUTT LOW THAT HAS TRANSITIONED TO
LARGE GYRE DRIFTING TOWARD THE MS VALLEY WILL CONTINUE TO DEAMPLIFY
ACROSS THE MIDWEST/OH VALLEY AREAS...EVENTUALLY MERGING WITH THE
STRONGER UPPER TROUGH MOVING EAST FROM THE PLAINS TO MS VALLEY.
..CNTRL PLAINS...
LARGE SCALE HEIGHT FALLS OF 30-60M/12H WILL ACCOMPANY THE MID/UPPER
LEVEL TROUGH SPREADING EAST FROM WY/CO TO NEB/SD DURING THE
AFTERNOON. INCREASINGLY STRONG DEEP-LAYER LIFT ALONG THE FRONTAL
ZONE...COUPLED WITH DIURNAL BOUNDARY LAYER HEATING/DESTABILIZATION
ACROSS THE PLAINS...WILL ACT TO GRADUALLY OVERCOME POTENTIALLY
STRONG CONVECTIVE INHIBITION. INITIAL STORMS WILL LIKELY SPREAD EAST
FROM THE HIGHER TERRAIN OF ERN WY/CO...WITH ADDITIONAL CONVECTION
POSSIBLE IN POST-FRONTAL REGIME ACROSS NRN NEB INTO CNTRL SD WHERE
CAP WILL BE WEAKER. WHILE INSTABILITY IN THESE AREAS WILL BE LESS
THAN FARTHER EAST/SOUTH ACROSS THE WARM SECTOR...A FEW CELLS COULD
PRODUCE HAIL GIVEN STRENGTH OF SHEAR/FORCING.
MORE INTENSE SURFACE-BASED CONVECTIVE DEVELOPMENT WILL ENSUE THROUGH
LATE AFTERNOON/EARLY EVENING INVOF FRONT AND FRONTAL WAVES FROM
CNTRL NEB TO SERN SD. VERY RICH BOUNDARY LAYER MOISTURE FOCUSED
ALONG THE FRONT AND NEAR EVOLVING SURFACE LOW WILL BOOST MLCAPE
VALUES TO OVER 2000 J/KG IN THE WARM SECTOR. WHILE EFFECTIVE SHEAR
ACROSS PARTS OF THE REGION WILL INITIALLY BE SOMEWHAT MARGINAL FOR
SUPERCELLS...GENERALLY AOB 20KT...FORCING AND INSTABILITY APPEAR
MORE THAN ADEQUATE FOR MULTICELL LINEAR ORGANIZATION NEAR THE FRONT.
DEEP LAYER SHEAR AND SUBSEQUENT STORM ORGANIZATION SHOULD INCREASE
INTO THE EVENING WITH BOTH LINEAR AND SUPERCELL STRUCTURES EVOLVING
ACROSS ERN NEB AND SD. DAMAGING WINDS AND LARGE HAIL APPEAR LIKELY
FROM THIS ACTIVITY. TORNADO POTENTIAL MAY ALSO EXIST IF DISCRETE
STORMS OCCUR NEAR CONSOLIDATING SURFACE LOW WHERE ENHANCED/STRONGER
LOW LEVEL SRH WILL LIKELY EXIST. IT IS POSSIBLE THAT A SMALL HIGHER
PROBABILITY SEVERE AREA MAY VERIFY OVER PARTS OF ERN NEB/SD THROUGH
THE EVENING. HOWEVER...IT IS TOO EARLY IN THE FORECAST PROCESS TO
INDICATE A HIGHER SEVERE THREAT AREA GIVEN UNCERTAINTIES REGARDING
MESOSCALE EVOLUTION.
ACTIVITY IS FORECAST TO CONGEAL INTO AN QUASI-LINEAR MCS/SQUALL LINE
THROUGH THE EVENING ACROSS THE MO RIVER VALLEY. AS MID LEVEL WIND
MAX ROTATES THROUGH THE BASE OF THE LARGER SCALE TROUGH OVERALL
PATTERN SUGGESTS DAMAGING WIND POTENTIAL MAY SPREAD EAST WITH THE
MCS ACTIVITY...FROM ERN SD/NEB INTO PARTS OF MN/IA...AND PERHAPS
KS/MO...THROUGH LATE TONIGHT.
..MN...
TSTMS ARE ALSO EXPECTED TO DEVELOP ALONG THE STATIONARY FRONTAL
BOUNDARY SITUATED SW-NE ACROSS MN THROUGH LATE TODAY AND TONIGHT.
WHILE SHEAR ALONG THIS PART OF THE BOUNDARY WILL BE GENERALLY
WEAK...POCKETS OF STRONGER DESTABILIZATION COINCIDENT WITH
FRONTAL/WAVE FORCING AND MODEST UNIDIRECTIONAL DEEP-LAYER FLOW COULD
SUPPORT A FEW SEVERE STORMS.
..KS...
ADDITIONAL CONVECTIVE DEVELOPMENT IS POSSIBLE FROM SW/SCNTRL NEB
INTO KS AS DRYLINE MIXES EAST ACROSS THESE AREAS THROUGH THE
AFTERNOON. THIS DEVELOPMENT MAY BE MORE ISOLATED GIVEN STRONG
INHIBITION FORECAST ACROSS THE AREA. HOWEVER...EFFECTIVE BULK SHEAR
AROUND 30KT WILL BE SUFFICIENT FOR SUPERCELL STORMS...POSSIBLY
BECOMING OUTFLOW DOMINANT GIVEN HOT AND DEEPLY MIXED BOUNDARY LAYER
ANTICIPATED.
..MID MS VALLEY...
LIFT ASSOCIATED WITH DEAMPLIFYING MID/UPPER WAVE SHOULD SPUR
NUMEROUS STORMS IN VERY MOIST REGIME FROM MO ACROSS IL THIS
AFTERNOON. WEAK/MOIST LAPSE RATES SUGGEST THAT OVERALL SEVERE
POTENTIAL WILL REMAIN LIMITED. HOWEVER...VERY MOIST/TROPICAL AIR
MASS ACCOMPANYING THIS SYSTEM...AND MODEST LOW LEVEL SHEAR...COULD
SUPPORT A WEAK/BRIEF TORNADO OR STRONG WIND GUST.
..AZ/NM...
ISOLATED/LOW PROBABILITY WIND/TORNADO THREAT MAY DEVELOP AS POCKETS
OF STRONGER DIURNAL INSTABILITY DEVELOP AMIDST RESIDUAL STRONGER
WIND FIELDS ASSOCIATED WITH DECAYING HENRIETTE CIRCULATION.
.CARBIN/GRAMS.. 09/06/2007
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