DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 200549
SWODY2
SPC AC 200547

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1247 AM CDT THU SEP 20 2012

VALID 211200Z - 221200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
MEAN LARGE-SCALE TROUGH WILL PERSIST FROM HUDSON BAY REGION SWD
ACROSS UPPER GREAT LAKES AND MS VALLEY. SERIES OF MOSTLY
LOW-AMPLITUDE/SUBTLE SHORTWAVES ARE EXPECTED TO TRAVERSE ASSOCIATED
CYCLONIC-FLOW FIELD OVER UPPER MIDWEST AND GREAT LAKES...WITH ONE
EXCEPTION. PRIMARY PERTURBATION CURRENTLY IS LOCATED OVER ARCTIC
COAST OF MAINLAND NUNAVUT...BASED ON MOISTURE CHANNEL IMAGERY. THIS
FEATURE IS FCST TO MOVE SWD ACROSS CENTRAL CANADA DURING NEXT COUPLE
DAYS...BECOMING ENTRAINED IN WRN/SWRN PORTION OF PREVAILING CYCLONIC
PATTERN AS IT CROSSES SERN MB/NRN MN THIS PERIOD. THIS TROUGH
SHOULD REACH ERN IA...NRN IL AND SRN WI REGION BY 22/12Z.

AT SFC...FRONTAL ZONE NOW ANALYZED ACROSS ERN LS...LM...NRN MO AND
SRN KS...WILL MOVE SLOWLY EWD ACROSS GREAT LAKES REGION AND WILL BE
REINFORCED ACROSS SRN PLAINS THROUGH DAY-2.

...NRN APPALACHIANS/OH VALLEY TO SRN PLAINS...
ISOLATED TO WIDELY SCATTERED TSTMS MAY DEVELOP INVOF SFC FRONTAL
ZONE IN ANY OF THREE REGIMES...EACH OF WHICH WILL BE STRONGLY
LIMITED IN SVR RISK BY LACK OF SHEAR AND/OR BUOYANCY --
1. CARRYOVER FROM DAY-1 OVERNIGHT PERIOD...WITH ELEVATED TSTMS
EMBEDDED IN WEAKENING REGIME OF LOW-LEVEL WAA AND MOISTURE
TRANSPORT. THIS IS MOST PROBABLE INVOF OZARKS/LOWER OH VALLEY
REGION...MOVING ENEWD TO NEWD AND WEAKENING DURING MIDDAY.
2 AND 3. DIURNAL DEVELOPMENT INVOF FRONT--WHICH MAY BE BIFURCATED
FURTHER INTO NRN APPALACHIAN/LOWER GREAT LAKES AND OZARKS REGIMES
DEPENDING ON STABILIZING EFFECTS OF CLOUDS/PRECIP FROM MORNING
ACTIVITY IN BETWEEN. NERN AREA WILL BE CHARACTERIZED BY STG
DEEP-LAYER SHEAR...BUT WEAKNESS OF BOTH INSTABILITY AND LOW-LEVEL
LIFT NEAR FRONTAL ZONE. OZARKS/AR/OK REGIME WILL HAVE DEEPLY MIXED
SUBCLOUD LAYERS...BUT ALSO...WEAK VERTICAL SHEAR AND LIMITED CAPE
DUE TO LACK OF MOISTURE. THIS BOUNDARY SHOULD ACCELERATE SEWD
ACROSS SRN PLAINS DURING PERIOD...THEN SWD OVER OZARKS AND NRN
MID-SOUTH REGION LATE IN PERIOD AS FRONTAL WAVE MOVES ENEWD ACROSS
REGION.

...UPPER GREAT LAKES REGION...
ISOLATED TO WIDELY SCATTERED...LOW-TOPPED TSTMS ARE POSSIBLE
PRIMARILY DURING AFTERNOON/EARLY EVENING HOURS. A FEW CELLS MAY
PRODUCE STG GUSTS OR HAIL NEAR SVR LIMITS...HOWEVER BUOYANCY APPEARS
TOO WEAK TO SUPPORT ORGANIZED SVR POTENTIAL. FCST SOUNDINGS SUGGEST
PATCHES OF DIURNAL HEATING...WITH TEMPS REACHING 60S F...WILL
SUFFICIENT TO REMOVE CINH. SPECIFIC BOUNDARIES/FOCI FOR DEVELOPMENT
APPEAR NEBULOUS...THOUGH WEAKLY BAROCLINIC SFC TROUGH SHOULD CROSS
WI/LM/LOWER MI DURING DAY. MLCAPE SHOULD REMAIN BELOW 500
J/KG...WITH SOME REACHING INTO THERMAL LAYER SUITABLE FOR LTG
PRODUCTION.

...SERN CONUS...
RESIDUAL FRONTAL ZONE...NOW ALIGNED SW-NE ACROSS CENTRAL GULF AND
NRN FL...SHOULD REMAIN OVER SAME GENERAL AREA THROUGH DAY-2...WITH
ONLY MESOSCALE PERTURBATIONS/MOVEMENTS. RICH LOW-LEVEL MOISTURE
NEAR FRONT...AND ALONG SEA BREEZE BOUNDARIES TO ITS S...WILL
CONTRIBUTE TO TSTM POTENTIAL. HOWEVER...WITH SVR THREAT VERY
LIMITED BY WEAKNESS OF BOTH SHEAR AND LAPSE RATES.

..EDWARDS.. 09/20/2012

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