DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 201732
SWODY2
SPC AC 201730

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT TUE AUG 20 2013

VALID 211200Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS UPPER MIDWEST...

...SYNOPSIS...
IN MID-UPPER LEVELS...MAIN STREAM OF NEARLY ZONAL FLOW CURRENTLY
EXTENDING ACROSS SRN CANADA AND EXTREME NRN CONUS IS FCST TO BUCKLE
SOMEWHAT THROUGH DAY-2 PERIOD. SHORTWAVE TROUGH WITH SEVERAL
ASSOCIATED VORTICITY MAXIMA -- NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY OVER CENTRAL-NRN AB -- IS FCST TO MOVE EWD AND AMPLIFY THIS
PERIOD...WITH EXPANDING VORTICITY RIBBON. BY 22/00Z...TROUGH SHOULD
PHASE WITH INITIALLY SEPARATE PERTURBATION OVER NRN HUDSON BAY...AND
EXTEND FROM NERN HUDSON BAY ACROSS NWRN ONT AND SRN PORTIONS MB/SK.
BY 22/12Z...TRAILING PORTION OF TROUGH SHOULD REACH LS AND MN
ARROWHEAD. MEANWHILE...WEAK MID-UPPER LOW NOW OVER IL IS EXPECTED
TO MOVE SLOWLY EWD FROM SRN INDIANA TO WV/OH BORDER REGION THROUGH
PERIOD...AS MAINLY OPEN-WAVE TROUGH WITH INTERMITTENT/EMBEDDED
CYCLONIC CIRCULATION. FARTHER W...MID-UPPER CYCLONE NOW MEANDERING
ERRATICALLY OFFSHORE CENTRAL CA COAST IS FCST TO MOVE SLOWLY
NEWD...REACHING SFO AREA NEAR END OF PERIOD.

SFC COLD FRONT -- NOW EXTENDING FROM SRN MB SWWD ACROSS DAKOTAS TO
NRN WY -- IS EXPECTED TO REACH FROM HUDSON BAY SWWD ACROSS NRN/WRN
MN TO NEB PANHANDLE BY START OF PERIOD. BY 22/00Z...FRONT SHOULD BE
NEAR MQT-MCW-LBF LINE...EITHER MERGING WITH OR JUST N OF WEAK LEE
CYCLONE LOCATED IN GLD-IML REGION. LEE THROUGH WILL EXTEND FROM
THERE SSWWD ACROSS ERN NM. BY END OF PERIOD...FRONT SHOULD EXTEND
FROM LH SWWD OVER CENTRAL/SRN IA TO SWRN NEB AND NERN CO. CENTRAL
PLAINS PORTION OF FRONT SHOULD BE QUASISTATIONARY THEN EXCEPT WHERE
EFFECTIVELY SHUNTED SWD BY MESOSCALE CONVECTIVE INFLUENCES.

...UPPER MIDWEST...
SCATTERED TO LOCALLY NUMEROUS TSTMS MAY DEVELOP INVOF SFC COLD FRONT
DURING AFTN...GROWING UPSCALE INTO CLUSTERED TO QUASI-LINEAR
CONFIGURATIONS AND PERSISTING INTO EVENING OVER PARTS OF THIS
CORRIDOR. DAMAGING GUSTS AND LARGE HAIL EACH WILL BE POSSIBLE.

DEVELOPMENT/MAINTENANCE OF THIS CONVECTION WILL BE AIDED BY
CONVERGENCE INVOF FRONT...STG DIURNAL HEATING...AND
NARROW/PREFRONTAL CORRIDOR OF FAVORABLE MOISTURE AND BUOYANCY.
EVAPOTRANSPIRATIVELY AIDED MOISTURE POOLING WILL CONTRIBUTE TO SFC
DEW POINTS COMMONLY IN 60S F. EXPANSIVE PREVALENCE OF NAM/SPECTRAL
SFC DEW POINTS IN 70S APPEARS UNSUPPORTED...BUT SUCH VALUES MAY
OCCUR IN POCKETS...ESPECIALLY OVER WI AND IA. STEEP MIDLEVEL LAPSE
RATES ATOP PREFRONTAL MOIST LAYER WILL CONTRIBUTE FURTHER TO MLCAPE
COMMONLY 2000-3000 K/KG...LOCALLY NEAR 4000 J/KG. DESPITE SWLY
LOW-LEVEL FLOW...ENOUGH VEERING WITH HEIGHT IS EVIDENT IN FCST
SOUNDINGS TO YIELD CURVED HODOGRAPHS....HOWEVER DEEP SHEAR WILL BE
MODEST...WITH MIDLEVEL FLOW ENHANCEMENT RELATED TO CANADIAN TROUGH
BEING LARGELY BEHIND SFC FRONT.

...CENTRAL HIGH PLAINS...
WIDELY SCATTERED TSTMS SHOULD DEVELOP DURING AFTN NEAR AND N OF SFC
FRONT...ESPECIALLY IN REGIME OF UPSLOPE/ELY BOUNDARY-LAYER WIND
COMPONENT THAT WILL PREVAIL FROM SWRN NEB INTO PORTIONS NERN CO AND
SERN WY. ISOLATED LARGE HAIL AND STG/DAMAGING GUSTS MAY OCCUR.
PROGGED HODOGRAPHS EXHIBIT STG CURVATURE IN REGION N OF SFC FRONT
AND LOW...BUT WITH WEAK SPEEDS LIMITING TOTAL SHEAR AND HELICITY IN
LOW-MIDDLE LEVELS. STILL...AT LEAST ISOLATED/TRANSIENT SUPERCELL
STRUCTURES ARE POSSIBLE. SFC DEW POINTS 50S IN CO/WY AND 60S OVER
NEB WILL COMBINE WITH DIURNAL HEATING TO SUPPORT 1000-2000 J/KG
MLCAPE.

...PORTIONS NRN CA...NWRN NV...SRN ORE...
SCATTERED TO WIDELY SCATTERED TSTMS SHOULD DEVELOP DURING AFTN AND
INTO EARLY EVENING ACROSS THIS REGION...AIDED AT FIRST BY DIABATIC
HEATING OF HIGHER TERRAIN AND AREAS OF LOCALIZED UPSLOPE FORCING.
HAIL/GUSTS NEAR SVR LEVELS MAY OCCUR.

AREA WILL LIE UNDER STG DIFLUENCE ALOFT LOCATED NE OF SLOWLY APCHG
MID-UPPER CYCLONE...AS WELL AS IN ZONE OF LOW-LEVEL MOISTURE
ADVECTION/TRANSPORT IN SUPPORT OF 40S TO 50S F SFC DEW POINTS AT
LOWER ELEVATIONS. ACCORDINGLY MODIFIED FCST SOUNDINGS INDICATE
500-1500 J/KG MLCAPE IS POSSIBLE. KINEMATICALLY...STRAIGHT TO
CLOCKWISE-CURVED LOW-LEVEL HODOGRAPHS ALSO SHOULD DEVELOP OVER
REGION...AMIDST 30-40 KT EFFECTIVE SHEAR MAGNITUDES...IN SUPPORT OF
ORGANIZED MULTICELLS. TRANSIENT SUPERCELL CHARACTERISTICS CANNOT BE
RULED OUT...FOR ANY RIGHTWARD-DEVIANT/NWD-MOVING CELLS.

..EDWARDS.. 08/20/2013

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