Wednesday, November 26, 2008

DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 261732
SWODY2
SPC AC 261730

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CST WED NOV 26 2008

VALID 271200Z - 281200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
UPPER AIR PATTERN THROUGH DAY-2 WILL BE DOMINATED BY SERIES OF STG
AND PROGRESSIVE SHORTWAVE TROUGHS AND LOWS. EASTERNMOST OF THESE --
CYCLONE CURRENTLY CENTERED OVER SERN QUE AND SERN ONT -- IS EXPECTED
TO LIFT NWD ACROSS WRN QUE. AS THIS OCCURS...UPSTREAM/OPEN-WAVE
TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER AB AND WRN MT
-- WILL DIG ESEWD ACROSS NRN PLAINS AND UPPER MS VALLEY...REACHING
VICINITY LS/WI BY 28/00Z BEFORE BECOMING POSITIVELY TILTED AND
ENTRAINED INTO CONFLUENT UPPER FLOW AROUND WRN QUE VORTEX.
MEANWHILE...SRN STREAM PERTURBATION -- NOW MANIFEST AS BROAD/CLOSED
CYCLONE OFFSHORE SRN CA -- IS FCST TO MOVE EWD TO CENTRAL/SRN GREAT
BASIN AND BEGIN DEVOLVING INTO OPEN-WAVE TROUGH BY 28/00Z. THIS
FEATURE WILL MOVE EWD INTO CONFLUENT UPPER FLOW AND ALSO BECOME
POSITIVELY TILTED AND WEAKER DURING ENSUING 12 HOURS. PORTION OF
UPPER LOW -- NOW OVER GULF OF AK -- IS EXPECTED TO MOVE SEWD ACROSS
BC AS OPEN SHORTWAVE TROUGH...REACHING SRN AB AND NRN ROCKIES BY
28/12Z AS RIDGE BREAKS DOWN N OF CA LOW/TROUGH.

DESPITE RELATIVELY COMPLEX AND SOMEWHAT INTERDEPENDENT CHAIN OF
HEIGHT TENDENCIES RELATED TO THESE FOUR PRIMARY
PERTURBATIONS...REMARKABLE AGREEMENT EXISTS AMONG MOST OPERATIONAL
PROGS AND SREF MEMBERS. THEREFORE...CONFIDENCE IS STG IN THIS BASIC
SCENARIO.

AT SFC...COLD FRONT IS ANALYZED OVER NRN MT -- PRECEDING NRN STREAM
SHORTWAVE TROUGH AND FCST TO MOVE QUICKLY SEWD ACROSS NRN/CENTRAL
PLAINS DAY-1. BY 28/00Z...FRONT SHOULD EXTEND FROM SFC LOW OVER
UPPER MI/LS AREA SWD ACROSS IL...THEN SWWD OVER AR AND W-CENTRAL TX.
FRONT WILL CONTINUE SEWD ACROSS WRN PORTIONS TN VALLEY...NRN
MS...AND CENTRAL/SW TX BY END OF PERIOD.

...SWRN CONUS...
ALTHOUGH UPPER TROUGH WILL BE WEAKENING WITH TIME...SUFFICIENT LARGE
SCALE ASCENT/COOLING ALOFT WILL SPREAD EWD ACROSS REGION TO SUPPORT
TSTM POTENTIAL...IN COMBINATION WITH AT LEAST MRGLLY FAVORABLE LOW
LEVEL MOISTURE. DIABATIC SFC HEATING DURING MIDDAY AND EARLY
AFTERNOON WILL BOOST LOW-MIDLEVEL LAPSE RATES FURTHER...PARTICULARLY
ACROSS PORTIONS CENTRAL/ERN AZ BEFORE TROUGH PASSAGE. MRGL BUOYANCY
-- E.G. MLCAPE GENERALLY AOB 300 J/KG AND WEAK CINH -- COMBINED WITH
LOCALLY ENLARGED LOW LEVEL HODOGRAPHS -- MAY PROMOTE A FEW ORGANIZED
TSTMS AND LINE SEGMENTS CAPABLE OF HAIL AND STG GUSTS.

...S-CENTRAL TX...WEST GULF COASTAL PLAIN...
CONDITIONAL SVR POTENTIAL EXISTS MAINLY FROM LATE AFTERNOON THROUGH
OVERNIGHT HOURS ACROSS THIS REGION...AMIDST TIGHTENING HEIGHT
GRADIENT ALOFT AND STRENGTHENING DEEP-LAYER SHEAR PROFILES
ASSOCIATED WITH APCHG SWRN CONUS TROUGH. IN ABSENCE OF SIGNIFICANT
COOLING ALOFT...AND WITH MODEST LOW LEVEL WAA
EXPECTED...LOW-MIDLEVEL LAPSE RATES SHOULD REMAIN RATHER WEAK AND
WILL LIMIT CONVECTIVE DEPTH AND COVERAGE FOR MUCH OF PERIOD. SO
WILL LACK OF MORE ROBUST LOW LEVEL FLOW AND CONVERGENCE INVOF
FRONTAL ZONE. HOWEVER...SFC DEW POINTS LOW-MID 60S F ARE POSSIBLE
OVER REGION AS PART OF MODIFIED RETURN FLOW REGIME...ALONG WITH DEW
POINTS 14-16 DEG C AROUND 925 MB. AREAS OF MLCAPES 500-800 J/KG MAY
DEVELOP -- ROOTED AT SFC BEFORE 00Z AND PERHAPS FOR A COUPLE HOURS
AFTERWARD.

..EDWARDS.. 11/26/2008

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