DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 180552
SWODY2
SPC AC 180551

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1251 AM CDT TUE SEP 18 2012

VALID 191200Z - 201200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
IN MID-UPPER LEVELS...MEAN TROUGHING WILL BE MAINTAINED FROM GREAT
LAKES TO WRN/CENTRAL GULF OF MEXICO. STG/EMBEDDED SHORTWAVE TROUGH
CURRENTLY OVER UPPER MS VALLEY REGION IS FCST TO PIVOT CYCLONICALLY
TO POSITION NEAR WRN NY...SERN ONT AND SWRN QUE BY 19/12Z. THIS
FEATURE WILL EJECT NEWD ACROSS ST. LAWRENCE RIVER/ERN QUE REGION TO
LABRADOR DURING DAY-2. STG SFC COLD FRONT -- NOW ANALYZED FROM
LOWER MI TO OZARKS AND TX SOUTH-PLAINS REGION -- IS FCST TO SWEEP
EWD/SEWD OVER OH/MS RIVER VALLEYS...MID-ATLC REGION AND SRN PLAINS
DAY-1...REACHING ERN NEW ENGLAND...NC OUTER BANKS...SERN GA AND
NERN/CENTRAL GULF BY 19/12Z. TRAILING SEGMENT OF FRONT WILL
DECELERATE/STALL ACROSS NRN FL FOR MUCH OF PERIOD...BEFORE
PROCEEDING SEWD AGAIN.

NEXT SUBSTANTIAL UPSTREAM PERTURBATION IS EVIDENT IN MOISTURE
CHANNEL IMAGERY OVER SERN YUKON...FAR NRN BC AND SWRN NW TERRITORIES
OF NWRN CANADA...CLOSE TO MEAN RIDGE POSITION. SHORTWAVE TROUGH
SHOULD MOVE SEWD AND AMPLIFY...REACHING WI...ERN MN AND LS BY
20/00Z...BEFORE EJECTING NEWD AND DEAMPLIFYING. ASSOCIATED SFC COLD
FRONT WILL MOVE SEWD ACROSS NRN PLAINS AND UPPER MS VALLEY THROUGH
MIDDLE OF PERIOD. BY 20/00Z...THIS BOUNDARY SHOULD REACH
LS...ERN/SRN WI...SRN IA...CENTRAL/SWRN KS AND NERN NM. BY
20/12Z...FRONT SHOULD REACH NRN/WRN LOWER MI...NRN IL...NWRN OK AND
E-CENTRAL NM. WEAK FRONTAL-WAVE LOW MAY DEVELOP OVERNIGHT IN WRN
OK.

...ERN NEW ENGLAND...EARLY PERIOD...
NARROW BAND OF STG NEAR-FRONTAL CONVECTION...MUCH OF WHICH MAY BE
TOO LOW-TOPPED FOR LTG GENERATION...WILL EXIT ERN NEW ENGLAND DURING
FIRST FEW HOURS OF PERIOD. FOREGOING AIR MASS WILL BE CHARACTERIZED
BY DEEP/NEARLY SATURATED THERMODYNAMIC PROFILES WITH WEAK TO NEUTRAL
LAPSE RATES...ATOP SHALLOW/STABLE SFC LAYER. SUBSTANTIAL SFC-BASED
INSTABILITY BY THEN SHOULD BE S OF AREA OVER ATLC WATERS. WHILE STG
GUSTS CANNOT BE RULED OUT WITH THIS ACTIVITY...ESPECIALLY OVER CAPE
COD AND NEARBY AREAS...PRIND SVR THREAT IS TOO MINIMAL TO WARRANT 5%
UNCONDITIONAL LINE.

...SRN PLAINS...
PREFRONTAL DRYLINE AND NEARLY COLLOCATED CONFLUENCE ZONE SHOULD
DEVELOP DURING AFTERNOON FROM SERN NM NEWD ACROSS TX PANHANDLE TO
SWRN KS. MOISTURE RETURN E OF THIS BOUNDARY WILL BE VERY
IMMATURE/INCOMPLETE...WITH TRAJECTORIES ARISING LARGELY FROM
POST-FRONTAL AIR MASS LEFT ACROSS SW TX/SERN NM BEHIND FIRST COLD
FRONT. STILL...NARROW CORRIDOR OF 50S F SFC DEW POINTS...WITH SMALL
POCKETS OF LOW-60S POSSIBLE...SHOULD DEVELOP IMMEDIATELY SE OF
DRYLINE/COLD FRONT BY 20/00Z. STG DIURNAL HEATING WILL STEEPEN
LOW-LEVEL LAPSE RATES AND YIELD DEEP/WELL-MIXED BOUNDARY LAYER WITH
MINIMAL CINH...BENEATH 500-1000 J/KG MLCAPE. THIS SHOULD SUPPORT
POTENTIAL FOR WIDELY SCATTERED/HIGH-BASED TSTMS DURING A FEW HOURS
OF LATE-AFTERNOON-EARLY EVENING. STG VEERING WITH HEIGHT IS LIKELY
BENEATH NWLY MID-UPPER FLOW...THOUGH DEEP SHEAR SHOULD REMAIN WEAK.
STG GUSTS MAY OCCUR WITH SOME OF THIS ACTIVITY.

...UPPER MIDWEST...UPPER GREAT LAKES...
SCATTERED TSTMS MAY DEVELOP INVOF SFC COLD FRONT DURING
AFTERNOON...WHEN THIS BOUNDARY IMPINGES UPON DIABATICALLY
DESTABILIZED AND MRGLLY MOIST CORRIDOR EXTENDING NEWD FROM
SRN-PLAINS REGIME. IMMEDIATE PREFRONTAL AIR MASS WILL BE AFFECTED
BY COMBINATION OF LOW-LEVEL WAA AND ERN PORTION OF STG COOLING ALOFT
ASSOCIATED WITH SHORTWAVE TROUGH. SFC-BASED CONVECTION DURING
MID-LATE AFTERNOON MAY BE MAINTAINED AND PERHAPS BUILD SWWD/NEWD
INVOF FRONT DURING EVENING...BUT WITH ELEVATED EFFECTIVE INFLOW
LAYERS. SMALL HAIL AND STG GUST CANNOT BE RULED OUT...BUT SVR
POTENTIAL IS GREATLY LIMITED BY LACK OF MORE ROBUST THETAE.

..EDWARDS.. 09/18/2012

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