SWODY1
SPC AC 020552
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CDT FRI SEP 02 2011
VALID 021200Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS ERN NEB TO WI SHORE OF
LM...
...SYNOPSIS...
IN MID-UPPER LEVELS...GEN REGIME OF NRN-STREAM TROUGHING OVER NRN
PLAINS WILL CONTINUE...AS SHORTWAVE TROUGHS MOVE THROUGH CYCLONIC
FLOW FIELD. POSITIVELY TILTED SHORTWAVE TROUGH NOW OVER ERN MT IS
EXPECTED TO EJECT NEWD FROM NRN MN ACROSS NRN ONT EARLY IN
PERIOD...WHILE DEAMPLIFYING. MEANWHILE...UPSTREAM SHORTWAVE TROUGH
-- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER CANADIAN ROCKIES
SHOULD EVOLVE NEARLY CLOSED 500-MB LOW OVER S-CENTRAL/SWRN SK BY
3/00Z...WITH TROUGH SWD OVER ERN MT. BY END OF PERIOD...TROUGH
SHOULD REACH SRN MB...WRN/CENTRAL ND AND NERN WY/WRN SD REGION.
AT SFC...COLD FRONT ASSOCIATED WITH FIRST NRN-STREAM SHORTWAVE
TROUGH IS EXPECTED TO CROSS UPPER MS VALLEY...MOVING TO NRN LOWER
MI...SWRN WI...CENTRAL IA..AND CENTRAL/SWRN KS BY 3/00Z. FRONT
SHOULD WEAKEN AND BECOME QUASISTATIONARY FROM NRN IL TO CENTRAL-WRN
KS BY END OF PERIOD. MEANWHILE...STRENGTHENING COLD
FRONT...PRECEDING SECOND NRN-STREAM SHORTWAVE...WILL MOVE SEWD
ACROSS NRN PLAINS TO NEAR ERN DAKOTAS...WRN NEB AND NERN CO BY
3/12Z.
...NEB TO UPPER GREAT LAKES...
CATEGORICAL OUTLOOK AREA REPRESENTS RELATIVELY DENSE CONCENTRATION
OF FCST CONVECTION JUXTAPOSED WITH FRONTAL LIFT AND LARGE BUOYANCY.
DOMINANT MODE SHOULD BE MULTICELLULAR...WITH DAMAGING GUSTS AND
LARGE HAIL BEING MAIN CONCERNS. SCATTERED TO LOCALLY NUMEROUS TSTMS
SHOULD DEVELOP IN THIS SWATH THIS AFTERNOON...AS SFC COLD FRONT
IMPINGES UPON CORRIDOR OF STG SFC HEATING AND FAVORABLE LOW-LEVEL
MOISTURE. VEERED AND RATHER WEAK SFC FLOW IN ADJOINING WARM-SECTOR
WILL LIMIT SHEAR THROUGH 0-1...0-3 AND 0-6 KM AGL LAYERS.
HOWEVER...BACKED/NELY WINDS ON IMMEDIATE N SIDE OF FRONT MAY
COINCIDE WITH SFC-BASED EFFECTIVE INFLOW PARCELS ENOUGH TO LENGTHEN
CONVECTIVELY ACCESSIBLE HODOGRAPHS AND DEEP-LAYER SHEAR
VECTORS...CONTRIBUTING TO POTENTIAL TSTM ORGANIZATION. WEAKER
MOISTURE MAKES SVR POTENTIAL MORE ISOLATED/CONDITIONAL FARTHER
W...WHILE LOWER MAGNITUDES OF BUOYANCY AND CONVERGENCE ARE EXPECTED
FROM LM ENEWD.
...CENTRAL HIGH PLAINS...
POSTFRONTAL ADVECTION OF MOIST AIR ATOP HIGHER TERRAIN...JUXTAPOSED
WITH STG SFC DIABATIC HEATING....SHOULD SUPPORT DEVELOPMENT OF
ISOLATED TO WIDELY SCATTERED TSTMS THIS AFTERNOON. WEAK NEAR-SFC
WINDS WILL LIMIT LOW-LEVEL HODOGRAPH SIZE AND BULK SHEAR.
HOWEVER...ERN CO WILL BE IN SRN FRINGES OF FAVORABLE WINDS
ALOFT...WITH 30-40 KT EFFECTIVE SHEAR MAGNITUDES POSSIBLE. AS
SUCH...ORGANIZED MULTICELLULAR TO MRGL SUPERCELLULAR TSTM MODES ARE
PSBL...WITH RISK OF HAIL. WELL-MIXED SUBCLOUD LAYER ALSO MAY
ENHANCE LOCALIZED POTENTIAL FOR STG-DAMAGING GUSTS.
...CENTRAL APPALACHIANS/PIEDMONT...
WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP THIS
AFTERNOON...MOVING GENERALLY SWD-SSWWD WITH POTENTIAL FOR ISOLATED
DAMAGING GUSTS AND HAIL NEAR SVR LIMITS. CONVECTION THEN SHOULD
WEAKEN AFTER DARK AS NEAR-SFC LAYER DIABATICALLY STABILIZES. SFC
DEW POINTS MID 60S TO LOW 70S F WILL CONTRIBUTE TO MLCAPE 1500-2500
J/KG MID-LATE AFTERNOON. ORGANIZATION OF SVR POTENTIAL WILL BE
LIMITED BY LACK OF MORE ROBUST DEEP-LAYER WIND FIELDS...ALTHOUGH STG
DIRECTIONAL SHEAR WILL OCCUR BENEATH MID-UPPER LEVEL NLYS.
...LA COAST...
PERIPHERAL AND CYCLONICALLY CURVING LLJ IS EXPECTED E-N OF CENTER OF
T.D. 13...AS LATTER DRIFTS NWWD TO NWD ACROSS NRN GULF PER NHC FCST.
THIS LLJ...ALREADY BEING SAMPLED BY LIX VWP...WILL CONTRIBUTE TO
ENLARGING HODOGRAPHS AND MRGL/CONDITIONAL TORNADO POTENTIAL
GENERALLY FROM CENTRAL LA COAST AND LOWER ATCHAFALAYA BASIN EWD TO
IMMEDIATE MS COAST. LOCALIZED CONVECTIVE MODE -- NAMELY DEVELOPMENT
OF SUSTAINED MINI-SUPERCELLS WITHIN ELONGATED PRECIP PLUME--WILL BE
KEY FACTOR IN ANY TORNADO THREAT. OTHER LIMITING FACTORS INCLUDE
EXTENSIVE COVERAGE OF CLOUDS/PRECIP ACTING TO RESTRICT AREAS OF
FAVORABLE DIABATIC DESTABILIZATION NEAR COAST. LOW-LEVEL
WINDS/SHEAR WILL WEAKEN WITH SUBSTANTIAL EXTENT INLAND. TORNADO
THREAT IS TOO ISOLATED/CONDITIONAL FOR CATEGORICAL OUTLOOK
ATTM...BUT MAY NEED UPGRADE IF CYCLONE WIND FIELDS SUBSTANTIALLY
STRENGTHEN IN MOST FAVORABLE LOW-LEVEL SHEAR SECTOR.
..EDWARDS/HURLBUT.. 09/02/2011
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