SWODY1
SPC AC 231227
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0727 AM CDT THU SEP 23 2010
VALID 231300Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL PLAINS INTO
THE UPPER MS VALLEY...
...SYNOPSIS...
STRONG UPPER SHORT WAVE TROUGH APPROACHING THE CENTRAL ROCKIES IS
FORECAST TO LIFT ENEWD AND GRADUALLY DEVELOP AN UPPER LOW OVER THE
UPPER MS VALLEY IN RESPONSE TO AN INTENSIFYING MID/UPPER LEVEL JET
STREAK ROTATING THROUGH THE SEWD QUADRANT OF THE SYSTEM. AT THE
SURFACE...A LOW OVER CENTRAL NEB WILL CONSOLIDATE AND SLOWLY DEEPEN
AS IT MOVES NEWD INTO MN BY LATE THIS AFTERNOON...AND OVER LAKE SUPR
TONIGHT. A COLD FRONT INITIALLY TRAILING SWWD FROM THE LOW WILL
SURGE EWD/SEWD TOWARD THE UPPER MS VALLEY BY EVENING...REACHING A
WRN LOWER MI/CENTRAL IL/SWRN MO/CENTRAL OK/ERN NM LINE BY 24/12Z.
...CENTRAL PLAINS INTO UPPER MS VALLEY...
AMPLE LOW LEVEL MOISTURE WITH SURFACE DEW POINTS IN THE MID/UPPER
60S IS EVIDENT FROM THE SRN/CENTRAL PLAINS ACROSS THE LOWER MO
VALLEY AND MID MS VALLEY. MOISTURE IS EXPECTED TO BE TRANSPORTED
NEWD TODAY TOWARD THE WRN GREAT LAKES AS STRONG SSWLY LOW LEVEL FLOW
EXPANDS ACROSS THE AREA IN ADVANCE OF THE APPROACHING COLD FRONT.
HOWEVER...COINCIDENT WITH THIS MOISTURE PLUME IS AN AXIS OF WARM MID
LEVEL TEMPERATURES WHICH WILL TEMPER LAPSE RATES AND MAGNITUDE OF
POTENTIAL INSTABILITY. FURTHERMORE...WIDESPREAD CLOUDS AND
PRECIPITATION SPREADING EWD FROM THE SRN HIGH PLAINS...CENTRAL
PLAINS...AND UPPER MS VALLEY WILL LIMIT DIURNAL HEATING AND
DESTABILIZATION...WITH MAXIMUM MLCAPE OF 500-750 J/KG EXPECTED AHEAD
OF THE COLD FRONT. CONCERN ABOUT THE WEAK THERMODYNAMIC ENVIRONMENT
IS THE PRIMARY LIMITING FACTOR FOR SEVERE STORM POTENTIAL.
THE POTENTIAL KINEMATIC CONTRIBUTION IS QUITE FAVORABLE WITH VERY
STRONG WIND FIELDS /60-70 KT AT 850 MB AND 70-80 KT AT 500 MB/
FORECAST FROM THE CENTRAL PLAINS INTO THE UPPER MS VALLEY...
RESULTING IN STRONG LOW- AND DEEP-LAYER VERTICAL SHEAR. DESPITE THE
OVERALL WEAK THERMODYNAMIC SUPPORT FOR INTENSE
CONVECTION...INCREASING LOW LEVEL CONVERGENCE ALONG THE COLD FRONT
IN THE WAKE OF THE CURRENT BROAD BAND OF CONVECTION MAY BE
SUFFICIENT FOR WIDELY SCATTERED THUNDERSTORMS TO DEVELOP THIS
AFTERNOON OVER CENTRAL/ERN KS...ERN NEB...AND WRN IA IN ASSOCIATION
WITH THE LEADING EDGE OF THE WATER VAPOR DRY INTRUSION. THE STRONG
VERTICAL SHEAR WILL ENHANCE STORM ORGANIZATION AND INTENSITY FOR ANY
SUSTAINED UPDRAFTS THAT CAN DEVELOP...WITH POTENTIAL FOR A FEW
SEVERE STORMS /INCLUDING ISOLATED SUPERCELLS/. DAMAGING WIND GUSTS
AND MARGINAL HAIL WILL BE THE MOST LIKELY THREATS...ALTHOUGH THE
STRENGTH OF THE LOW LEVEL SHEAR AND LOW LCL HEIGHTS MAY ALSO PROMOTE
DEVELOPMENT OF A BRIEF TORNADO OR TWO.
IN ADDITION...STRONG ISALLOBARIC FORCING COUPLED WITH FRONTAL
CONVERGENCE SUGGEST POTENTIAL FOR A FAST MOVING LOW-TOP CONVECTIVE
LINE WITH EMBEDDED BOWS/LEWPS TO FORM OVER PARTS OF SRN MN INTO NRN
IA THIS AFTERNOON MOVING INTO WI THIS EVENING. VERTICAL TRANSPORT OF
STRONG HORIZONTAL MOMENTUM WITHIN THE FRONTAL ZONE WILL BE ENHANCED
BY CO-LOCATED CONVECTIVE DOWNDRAFTS AND CONTRIBUTE TO A RISK OF
DAMAGING WIND GUSTS.
ALTHOUGH CONVECTION IS LIKELY TO PERSIST INTO THE OVERNIGHT
HOURS...THE OVERALL SEVERE THREAT IS EXPECTED TO DIMINISH THIS
EVENING AS THE NOCTURNAL BOUNDARY LAYER BEGINS TO COOL AND
STABILIZE.
..WEISS/SMITH.. 09/23/2010
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