SWODY1
SPC AC 201249
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT TUE SEP 20 2011
VALID 201300Z - 211200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
PROGRESSIVE UPR FLOW REGIME WILL CONTINUE TODAY WITH THE UPR TROUGH
FROM NY TO THE CNTRL GULF COAST MOVING TO THE ATLC SEABOARD BY
TONIGHT. IMPULSE EMBEDDED ALONG SRN EXTENT OF THE LARGER SCALE
TROUGH WILL TRAVEL FROM THE CNTRL GULF COAST REGION TO THE CAROLINAS
TDY WHILE WEAKENING. A WEAK SFC LOW/TRIPLE POINT WILL ADVANCE
INLAND ACROSS PORTIONS OF THE ERN GULF COAST REGION...PERHAPS AS FAR
N AS SRN GA THIS AFTN.
MEANWHILE...TO THE W...A COMPACT UPR LOW OVER THE DAKOTAS WILL MOVE
INTO THE UPR GRTLKS REGION THIS EVENING. SFC CYCLONE WILL MOVE TO
LK SUP WHILE A CDFNT SWEEPS E AND SE INTO THE CNTRL GRTLKS REGION
AND SRN PLAINS BY 12Z WED.
...UPR GRTLKS/UPR MS RVR VLY...
LEADING BANDS OF ASCENT EMANATING FROM THE STRONG PV-MAX OVER THE
DAKOTAS WILL BE RESPONSIBLE FOR PRE-FRONTAL CONVECTION OVER THE
REGION THIS MORNING. GUSTY WINDS MAY ACCOMPANY THIS ACTIVITY.
CONCERN WILL THEN FOCUS ON PSBL DEVELOPMENT OF SFC-BASED STORMS THIS
AFTN...ARCING FROM NRN MN SSEWD INTO THE UPR MS RVR VLY ALONG THE
PRIMARY CDFNT/SFC LOW. LEADING EDGE OF STRONG ASCENT TIED TO THE
UPR LOW WILL SPREAD ACROSS THE WARM SECTOR BY EARLY AFTN/ONSET OF
PEAK HEATING. PREFRONTAL AIR MASS WILL BE CHARACTERIZED BY WEAK
THERMAL BUOYANCY/MEAGER LLVL MOISTURE AND MLCAPES SHOULD REMAIN LESS
THAN 500 J/KG. HOWEVER...STEEPENING MID-LVL LAPSE RATES AND STRONG
DYNAMICS WILL LIKELY FORCE A LINE OF LOW-TOPPED STORMS WITH PSBL
EMBEDDED SUPERCELLS GIVEN 50+ KTS OF WLY EFFECTIVE SHEAR. IN
FACT...IF SUFFICIENT 0-3KM CAPE CAN MATERIALIZE NEAR THE TRACK OF
THE SFC LOW...FCST HODOGRAPHS EXHIBIT STRONG 0-1KM SHEAR AND A BRIEF
TORNADO CANNOT BE RULED OUT OVER FAR NE MN AND NWRN WI.
OTHERWISE...DMGG WIND GUSTS AND SVR HAIL WILL BE PSBL. ACTIVITY
WILL LIKELY BACKBUILD SWWD ALONG THE CDFNT INTO THE UPR MS VLY
OVERNIGHT WITH FAST MOVING CONVECTION SHIFTING DOWNSTREAM INTO THE
CNTRL GRTLKS REGION OVERNIGHT. THE SVR THREATS SHOULD DIMINISH
HOWEVER...OWING TO WANING INSTABILITY.
...ERN GULF COASTAL REGION...
SWRN FRINGE OF A LLVL STABLE WEDGE WILL MODIFY AS THE WRMFNT FROM
CNTRL AL TO THE FL PNHDL RETREATS NEWD AHEAD OF THE AFOREMENTIONED
WEAK UPR IMPULSE. MAINTENANCE OF MODEST WARM ADVECTION PROFILES
AHEAD OF THE EJECTING SYSTEM WILL ENCOURAGE CONVECTION TO DEVELOP
ALONG/N OF THE FRONT THROUGH THE DAY...BUT POCKETS OF WEAK
INSOLATION TO THE SW WILL LOCALLY STEEPEN LAPSE RATES AND BOOST
BUOYANCY. RELATIVELY RICH MOIST LLVL AIR MASS AND WEAK ESELY WINDS
BELOW 1-2KM NEAR THE WRMFNT WILL FAVOR A LOW-END POTENTIAL FOR
SFC-BASED STORMS THAT MAY PRODUCE LOCAL DMGG WINDS/ISOLD TORNADO
FROM SERN AL INTO SRN GA AND NRN FL THIS AFTN.
..RACY/COHEN.. 09/20/2011
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