DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 201730
SWODY2
SPC AC 201729

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
ISSUED BY 15TH OWS SCOTT AIR FORCE BASE IL
1229 PM 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 JUST NORTH OF
MANITOBA...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 WRN
MI...ERN IA...NRN IL AND SRN WI REGION BY 22/12Z.

AT SFC...FRONTAL ZONE NOW ANALYZED ACROSS WRN MI...NRN IL...CNTRL MO
AND NRN OK...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--WITH ENERGY SPLIT BETWEEN
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 BE
SUFFICIENT TO REMOVE CINH. SPECIFIC BOUNDARIES 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.

..15_OWS.. 09/20/2012

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