DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 211726
SWODY2
SPC AC 211724

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1224 PM CDT WED AUG 21 2013

VALID 221200Z - 231200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
IN MID-UPPER LEVELS...NRN STREAM IS FCST TO BECOME SOMEWHAT MORE
AMPLIFIED THROUGH DAY-2. SHORTWAVE TROUGH -- NOW EVIDENT IN
MOISTURE CHANNEL IMAGERY OVER SK -- IS FCST TO MOVE ESEWD AND
STRENGTHEN. PERTURBATION SHOULD REACH LS BY 22/12Z...SERN ONT/SWRN
QUE BY 23/00Z...AND MAINE BY END OF PERIOD. IN ADVANCE OF THAT
SYSTEM...WEAK TROUGH NOW OVER INDIANA SHOULD MOVE OFFSHORE MID-ATLC
AND NC AROUND 23/00Z. FARTHER W...WEAK PERTURBATION NOW OVER SRN ID
BORDER REGION IS EXPECTED TO MIGRATE SLOWLY THROUGH MEAN RIDGE
POSITION OVER NRN ROCKIES...REACHING SRN MT AND NRN WY AROUND
23/00Z...AND WRN SD OVERNIGHT. PERSISTENT/WELL-DEFINED MID-UPPER
CYCLONE...INITIALLY LOCATED OFFSHORE CENTRAL CA -- IS EXPECTED TO
DEVOLVE TO OPEN-WAVE TROUGH EARLY IN PERIOD WHILE MOVING ASHORE
BETWEEN SFO AND CAPE MENDOCINO. RESULTING SHORTWAVE TROUGH SHOULD
MOVE NNEWD ACROSS NRN CA AND SRN/CENTRAL ORE THROUGH REMAINDER
PERIOD...WHILE CONTINUING TO DEAMPLIFY.

AT SFC...COLD FRONT WAS EVIDENT FROM NERN MN SWWD ACROSS
E-CENTRAL/S-CENTRAL SD TO NERN WY. BY 22/12Z...FRONT SHOULD BE
LOCATED FROM LH TO SRN WI TO CENTRAL IA...SRN NEB AND NERN CO.
NEB/CO SEGMENT OF FRONT SHOULD MOVE LITTLE THROUGH DAYLIGHT
HOURS...WHILE ERN PORTION OF FRONT PROCEEDS TO ST LAWRENCE VALLEY
AREA OF SRN QUE...LE...NRN INDIANA...CENTRAL IL...AND NRN MO BY
23/00Z. AT THAT TIME...SFC TROUGH SHOULD EXTEND FROM FRONTAL
INTERSECTION OVER NERN CO/SWRN NEB REGION SWD ACROSS ERN
CO...PERHAPS WITH WEAK/ACCOMPANYING LOW. BY END OF PERIOD...FRONT
SHOULD EXTEND FROM NEAR NEW ENGLAND COAST SWWD ACROSS CENTRAL
APPALACHIANS...THEN WWD OVER SRN IL...WHILE MOVING NWD AS WARM FRONT
OVER PORTIONS ERN NEB AND WRN SD.

...NERN CONUS...
WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP INVOF SFC COLD
FRONT DURING AFTN...OVER LOWER GREAT LAKES REGION...WITH ADDITIONAL
TSTMS POSSIBLE ENEWD ACROSS SRN QUE AND NRN MAINE. ISOLATED
DAMAGING GUSTS APCHG SVR LIMITS ARE POSSIBLE. ALTHOUGH STRONGEST
FLOW ALOFT SHOULD REMAIN BEHIND SFC COLD FRONT...LARGE-SCALE ASCENT
WILL INCREASE THROUGH AFTN ABOVE FRONT WITH APCH OF SHORTWAVE
TROUGH. SFC DEW POINTS GENERALLY 60S F...ALONG WITH PREFRONTAL
BOUNDARY-LAYER HEATING...WILL OFFSET WEAK LAPSE RATES ALOFT ENOUGH
TO SUPPORT 500-1000 J/KG MLCAPE OVER MAINE AND NY...AND 1000-1500
J/KG SWWD OVER PORTIONS PA/OH. LACK OF STRONGER PRESENCE OF AT
LEAST THESE THREE FACTORS...DEEP-LAYER LAPSE RATES...LOW-LEVEL
FLOW...AND VERTICAL SHEAR...APPEARS TO PRECLUDE MORE
SUBSTANTIAL/ORGANIZED SVR THREAT.

...CENTRAL HIGH PLAINS...
BY MID-LATE AFTN...LIGHT ELY/NELY FLOW NEAR FRONT AND NW OF LEE
TROUGH/LOW SHOULD ADVECT FAVORABLE LOW-LEVEL MOISTURE ONTO HIGHER
TERRAIN OF SERN WY AND NERN CO...WITH DEW POINTS RANGING FROM 50S F
THERE TO 60S ACROSS PORTIONS SWRN/CENTRAL NEB. WIDELY SCATTERED
TSTMS SHOULD DEVELOP DURING AFTERNOON IN THOSE AREAS. ADDITIONAL
CONVECTION IS POSSIBLE ALONG NRN EDGE OF STRONGLY HEATED/MIXED AIR
OVER SWRN NEB/NWRN KS. ISOLATED SVR HAIL AND/OR DAMAGING GUSTS MAY
OCCUR. THOUGH STG DIRECTIONAL SHEAR IS EXPECTED IN THIS
REGIME...WEAK LOW-LEVEL SPEEDS WILL LIMIT HODOGRAPH SIZE...AND LACK
OF STRONGER MID-UPPER WINDS WILL RESTRICT DEEP SHEAR. AS SUCH...ANY
SUPERCELL POTENTIAL APPEARS MRGL/TRANSIENT...AND OVERALL SVR THREAT
APPEARS RATHER DISORGANIZED.

...NRN CA...NWRN NV...SRN ORE...
APCHG SHORTWAVE TROUGH WILL LEAD TO STRENGTHENING MID-UPPER FLOW
THROUGH AFTN ACROSS PARTS OF THIS AREA -- E.G. 60-70 KT AT 250 MB
AND 30-40 KT AT 500 MB -- AS WELL AS INCREASING DCVA/UVV ALOFT.
LATTER WILL COMBINE WITH DIABATIC SFC HEATING TO YIELD FAVORABLY
STEEP LOW-MIDDLE LEVEL LAPSE RATES...ACCOMPANIED BY ENOUGH PW TO
SUPPORT 40S-50S F SFC DEW POINTS IN LOWER ELEVATIONS. WIDELY
SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP DURING AFTN AND MOVE
PRIMARILY NWD TO NNEWD. MODIFIED FCST SOUNDINGS SUGGEST 500-1000
J/KG MLCAPE AND 30-45 KT EFFECTIVE SHEAR MAGNITUDES...IN SUPPORT OF
ISOLATED SVR GUST/HAIL POTENTIAL WITH THIS CONVECTION.

..EDWARDS.. 08/21/2013

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