DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 031251
SWODY1
SPC AC 031249

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT MON SEP 03 2012

VALID 031300Z - 041200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER
MIDWEST...

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF MS/AL...

...SYNOPSIS...
WATER VAPOR SATELLITE IMAGERY AND OBJECTIVE UPPER AIR DATA REVEAL A
COMPLEX FLOW FIELD ACROSS THE CONTINENT AND NEAR SHORE WATERS THIS
MORNING. FASTER W-SWLY FLOW ACROSS THE NORTHWEST/NRN PLAINS/UPPER MS
VALLEY IS COMPRISED OF A SHORTWAVE TROUGH CROSSING LS AND WI ATTM
AND ANOTHER UPSTREAM IMPULSE SPREADING EAST FROM MT. WEAKER
DISTURBANCES ALSO EXIST AMIDST A PLUME OF MONSOON MOISTURE EXTENDING
ALONG THE NRN FLANK OF THE SUBTROPICAL RIDGE FROM THE SW/FOUR
CORNERS ENEWD ACROSS THE CNTRL PLAINS. THE RESIDUAL TROPICAL
CIRCULATION THAT WAS ISAAC REMAINS CUTOFF FROM THE FASTER WLYS TO
THE NORTH AND DEEP LAYER ELY FLOW ACROSS THE GULF AND FL. A COLD
CORE MID/UPPER LEVEL LOW EMBEDDED WITHIN THE ELYS WAS TRACKING WWD
TOWARD SRN FL.

AT THE SFC...A STATIONARY FRONT SEPARATES COOLER/DRIER AIR OVER THE
NORTHEAST FROM WARM AND VERY MOIST AIR FROM DELMARVA SOUTH AND WEST.
FORMER ISAAC LOW ACROSS THE LOWER OH VALLEY IS FORECAST TO MOVE
LITTLE THIS PERIOD. CONVECTION ASSOCIATED WITH THE REMNANTS OF ISAAC
CONTINUES AS A DECAYING MCS OVER AL THIS MORNING. FARTHER NORTH...A
WEAK COLD FRONT EXTENDS FROM A LOW IN CANADA SWWD ACROSS LS/MN
BEFORE TRANSITIONING INTO A WARM FRONT ORIENTED SE-NW ACROSS THE
DAKOTAS. ANOTHER WEAK COLD FRONT WAS TAKING FORM ACROSS ERN MT AND
WAS PRECEDED BY SFC TROUGH OVER ND. MOST OF THESE SFC FEATURES...IN
CONCERT WITH SOME UPPER AIR SUPPORT...WILL PLAY A ROLE IN TSTM
DEVELOPMENT TODAY.

...UPPER MIDWEST...
DEVELOPMENT OF A BROKEN SQLN OVER LS THIS MORNING WAS AIDED BY
DEEP-LAYER ASCENT ACCOMPANYING THE SHORTWAVE TROUGH AND WEAK COLD
FRONT SPREADING EAST ACROSS THE REGION. LOW LEVEL MOISTURE TRANSPORT
INTO AND AHEAD OF THE SLOWLY ADVANCING WEAK FRONTAL ZONE...AND AHEAD
OF TRAILING SHORTWAVE DISTURBANCES OVER MN AND NEB ATTM...WILL
PROMOTE MODEST DESTABILIZATION ACROSS THE REGION THROUGH THE MORNING
AND INTO THIS AFTERNOON. MLCAPE FROM ERN NEB AND IA/SERN MN INTO WI
SHOULD CLIMB TO AROUND 1500 J/KG AMIDST MODEST CAPPING/INHIBITION.
WEAK BUT PERSISTENT HEIGHT FALLS ACROSS THE REGION WILL MAINTAIN
ASCENT BOTH ALONG THE FRONT AND ACROSS WARM SECTOR WITH THE
LIKELIHOOD OF ADDITIONAL STORMS DEVELOPING THROUGH THE DAY. WEAK LOW
LEVEL FLOW TOPPED BY 25-35KT WLY FLOW AT 500MB SHOULD SUPPORT SOME
STORM UPDRAFT PERSISTENCE/ROTATION WITH A FEW STORMS CAPABLE OF
PRODUCING HAIL AND HIGH WINDS. A SMALL MCS OR TWO MAY EVOLVE FROM
STORM MERGERS INTO THE EVENING WITH STORM SCALE ENSEMBLE GUIDANCE
INDICATING A GREATER CHANCE FOR THIS TO OCCUR ACROSS THE MID MO
RIVER VALLEY INTO LATE TONIGHT.

...MS/AL...
SWRN FLANK OF DECAYING MCS COLD POOL ACROSS THE MS/AL BORDER AREAS
WILL LIKELY SERVE TO FOCUS NEW CONVECTIVE DEVELOPMENT AS AIRMASS IN
THIS AREA BECOMES STRONGLY UNSTABLE /MLCAPE AOA 2000 J/KG/ THROUGH
THE AFTERNOON. LARGER SCALE FORCING FOR ASCENT ACROSS THIS AREA WILL
REMAIN SUBTLE/WEAK WHICH COULD DELAY MORE ROBUST/WIDESPREAD STORM
DEVELOPMENT UNTIL LATER IN THE DAY OR THIS EVENING. HOWEVER...WEAK
INHIBITION AND VEERING WIND PROFILES THROUGH A DEEP LAYER SUGGEST
THAT ROBUST/ORGANIZED STORMS WILL EVENTUALLY DEVELOP AND LIKELY
PERSIST. ANOTHER MCS MAY FORM BY LATE EVENING AND...IN ADDITION TO
LOCALLY HEAVY TO EXTREME RAINFALL...DAMAGING WINDS AND TORNADO
POTENTIAL WILL ALSO ACCOMPANY SOME OF THE STRONGER STORMS.

...CNTRL/NRN PLAINS...
AT LEAST ISOLATED HIGH-BASED STORMS APPEAR POSSIBLE NEAR WARM
FRONT/LEE TROUGH THIS AFTERNOON FROM THE CNTRL HIGH PLAINS TO
ND...AND EVENTUALLY INTO WRN MN LATER TONIGHT AS THE MT SHORTWAVE
TROUGH SPREADS EAST. WHILE THIS DEVELOPMENT WILL OCCUR AMIDST
GENERALLY WEAKER INSTABILITY THAN FARTHER EAST AND SOUTH...STEEP MID
LEVEL LAPSE RATES AND SUFFICIENT SHEAR COULD CONTRIBUTE TO A COUPLE
OF HAIL/WIND EVENTS.

...FL...
COLD CORE UPPER LOW WILL BOOST TSTM POTENTIAL ACROSS SRN FL WITH
SOME CHANCE FOR HAIL AND PERHAPS A WET DOWNBURST OR TWO.

...SOUTHEAST/MID ATLANTIC...
WEAK UPPER DIVERGENCE SPREADING EAST AHEAD OF REMNANT ISAAC TROUGH
WILL AID ASCENT AND SLOW-MOVING TSTM DEVELOPMENT ALONG STALLED
FRONTAL ZONE ACROSS THE MID ATLANTIC. IN ADDITION...WEAK UPSLOPE
FLOW INTO THE PIEDMONT AND APPALACHIAN FOOTHILLS WILL LIKELY
CONTRIBUTE TO SCATTERED/NUMEROUS STORMS FROM GA ACROSS THE CAROLINAS
THIS AFTERNOON. SHEAR WILL NOT BE PARTICULARLY STRONG SO POORLY
ORGANIZED MULTICELL STORMS ARE ANTICIPATED WITH SOME CHANCE FOR
ISOLATED WIND DAMAGE.

..CARBIN/ROGERS.. 09/03/2012

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