DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 160600
SWODY2
SPC AC 160559

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT SUN SEP 16 2012

VALID 171200Z - 181200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
UPPER-AIR PATTERN FCST TO BEGIN SUBSTANTIAL AMPLIFICATION DURING
PERIOD...RELATED IN PART TO SHORTWAVE TROUGH NOW LOCATED OVER
PORTIONS SK/AB. WHILE ERN PORTION OF RELATED VORTICITY FIELD BREAKS
EWD TOWARD SRN HUDSON BAY...WRN PORTION WILL DIG SEWD ACROSS NRN
PLAINS DAY-1. BY 17/12Z...EXPECT STRENGTHENING TROUGH FROM NWRN ONT
SWWD ACROSS SD TO WRN NEB. THIS FEATURE SHOULD AMPLIFY FURTHER AND
BECOME PROGRESSIVELY LESS POSITIVELY TILTED WITH TIME -- REACHING
CENTRAL/ERN MN...WRN IA AND ERN/SRN NEB. BY 18/00Z...THIS FEATURE
SHOULD EXTEND FROM WRN/CENTRAL LS SSWWD ACROSS MO...PART OF
FULL-LATITUDE TROUGHING REGIME FROM HUDSON BAY TO NWRN GULF.

SRN-STREAM PERTURBATION -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
OVER W TX...EXTREME SERN NM AND CHIHUAHUA...SHOULD MOVE EWD ACROSS
MUCH OF TX DAY-1 INTO EARLY DAY-2...REACHING SE TX/SWRN LA AREA BY
18/00Z. PHASE-SPEED AND AMPLITUDE PROGS FOR THIS SYSTEM BECOME MORE
DISPARATE AFTER ABOUT 17/18Z...RELATED TO DIFFERENCES IN INFLUENTIAL
NRN-STREAM AMPLIFICATION AND HEIGHT FALLS. BY 18/12Z...THIS FEATURE
WILL BE DEAMPLIFYING...SOMEWHERE FROM CENTRAL/ERN LA TO AL.

AT SFC...FRONTAL-WAVE LOW SHOULD DEVELOP BY 17/12Z INVOF NERN WI OR
ERN UPPER MI...MOVING EWD ACROSS NECK OF ONT THROUGH REMAINDER
PERIOD. TRAILING/STRENGTHENING STG COLD FRONT IS FCST TO SWEEP
SEWD/SWD ACROSS UPPER-MID MS VALLEY AND CENTRAL/SRN PLAINS THROUGH
PERIOD...REACHING WRN LOWER MI...CENTRAL IL...SWRN MO...SWRN OK AND
SERN NM BY 18/00Z. BY END OF PERIOD...FRONT SHOULD REACH
OH...MIDDLE-ERN TN...AL AND NWRN GULF.

...UPPER GREAT LAKES TO MO AND OK...
WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP INVOF SFC COLD
FRONT DURING AFTERNOON...FORMING BKN BAND FROM PORTIONS NRN LM/ERN
UPPER MI/NRN LOWER MI REGION SWWD ACROSS MO. WELL-MIXED SUBCLOUD
LAYERS AND AT LEAST MRGL LOW-LEVEL MOISTURE -- WITH SFC DEW POINTS
GENERALLY LOW-MID 60S F -- WILL OFFSET MODEST LAPSE RATES ALOFT
ENOUGH TO YIELD PEAK AFTERNOON MLCAPE AROUND 1500 J/KG. MAIN
LIMITING FACTORS WILL BE LACK OF BOTH VERTICAL SHEAR AND STEEPER
LAPSE RATES ALOFT...EACH RELATED TO PRESENCE OF STRONGEST DEEP-LAYER
ASCENT REMAINING BEHIND SFC COLD FRONT THROUGH MOST OF PERIOD. AS
SUCH...ORGANIZATION OF SVR THREAT WILL BE POOR...THOUGH A FEW
STG/DAMAGING GUSTS ARE POSSIBLE.

WIDELY SCATTERED TSTMS ALSO MAY DEVELOP FARTHER SW ACROSS PORTIONS
OK DURING AFTERNOON...AND NRN/CENTRAL TX OVERNIGHT...ALONG AND
BEHIND FRONT. A FEW STG GUSTS ALSO MAY OCCUR WITH ANY AFTN TSTMS
OVER OK THAT HAVE ACCESS TO WELL-MIXED/WARM-SECTOR AIR MASS...BUT
THIS AREA ALSO WILL BE CHARACTERIZED BY DRIER SFC CONDITIONS AND
WEAKER FRONTAL LIFT THAN FARTHER NE.

...TN VALLEY TO SRN APPALACHIANS/SRN PIEDMONT REGIONS...
WIDELY SCATTERED TO SCATTERED TSTMS ARE POSSIBLE THROUGHOUT
PERIOD...POTENTIALLY BECOMING BETTER ORGANIZED OVERNIGHT. FACTORS
PRECLUDING UNCONDITIONAL SVR PROBABILITIES ATTM INCLUDE LIMITED
INSTABILITY...AMBIGUOUS LOW-LEVEL FOCI...AND PROGS OF WEAK SFC FLOW
MAGNITUDES. COOL-AIR DAMMING REGIME ALSO WILL LINGER FOR MOST OF
PERIOD OVER HIGHER TERRAIN. HOWEVER...RICH LOW-LEVEL MOISTURE WILL
ADVECT NWD ACROSS MUCH OF THIS REGION...ESPECIALLY FROM ABOUT 18/00Z
ONWARD...BENEATH PLUME OF STRENGTHENING MID-UPPER WINDS RELATED TO
PHASING OF NRN/SRN STREAM PERTURBATIONS. 850-MB WINDS ALSO WILL
STRENGTHEN OVERNIGHT ACROSS GA/SC...LEADING TO INCREASING LOW-LEVEL
SHEAR ATOP FEEBLE SFC WINDS. CONDITIONAL CONCERN EXISTS FOR
LOW-TOPPED SUPERCELLS...PERHAPS WITH LITTLE OR NO LTG.
PROBABILITIES MAY BE INTRODUCED ONCE PROGS OF MID-UPPER PERTURBATION
AND RELATED LOW-LEVEL RESPONSE BECOME MORE CONSISTENT...AND/OR
LATE-PERIOD MECHANISMS FOR PREFRONTAL CONVECTIVE FORCING ARE
BETTER-DEFINED.

..EDWARDS.. 09/16/2012

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