SWODY1
SPC AC 122000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT MON MAR 12 2012
VALID 122000Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS CNTRL/SRN LOWER MI...FAR NERN
IL...NRN IND/OH...
...MIDWEST/GREAT LAKES AREA THROUGH TONIGHT...
CORRIDOR OF STRONGER SURFACE HEATING HAS RESULTED IN 19Z
TEMPERATURES HAVING REACHED THE MIDDLE 60S TO LOWER 70S FROM SWRN
LOWER MI SWWD. INITIAL LOBE OF FORCED ASCENT AND SMALL MCS OVER
W-CNTRL LOWER MI SHOULD PROPAGATE E/ENEWD ON THE FRINGE OF THE
GREATER HEATING. MORNING CONVECTION-ALLOWING AND OPERATIONAL MODEL
GUIDANCE CONTINUE TO SUPPORT THE SCENARIO FOR CONVECTION
BACKBUILDING SWWD AS WEAK COLD FRONT SWEEPS ACROSS THE WARM SECTOR.
IT APPEARS PROBABLE A SW/NE-ORIENTED BAND OF TSTMS WOULD FORM BY
EARLY EVENING FROM SRN LOWER MI INTO NRN IND. DEEP-LAYER FLOW WOULD
BE NEARLY PARALLEL TO THIS TYPE OF ORIENTATION AND MAY MITIGATE A
MORE ROBUST DAMAGING WIND THREAT. STILL...DID EXPAND SLIGHT RISK
SLIGHTLY SEWD WITH POTENTIAL FOR AN ORGANIZED /BUT WEAKENING/ LINE
PROGRESSING INTO NRN OH/LK ERIE VICINITY TONIGHT.
...LOWER MS VALLEY TO THE MID-SOUTH THROUGH EARLY TONIGHT...
TSTM CLUSTERS HAVE PERSISTED THROUGH THE DAY ALONG REMNANT
CONVECTIVE OUTFLOW ACROSS SRN LA WITH ATTENDANT MARGINAL SEVERE
RISK. FARTHER N...THE LIKELIHOOD FOR A FOCUSED AREA OF TSTM
DEVELOPMENT APPEARS TO HAVE DIMINISHED...AND WILL ONLY MAINTAIN LOW
SEVERE PROBABILITIES FOR ANY ISOLATED TSTMS THAT MAY FORM.
..GRAMS.. 03/12/2012
.PREV DISCUSSION... /ISSUED 1130 AM CDT MON MAR 12 2012/
...SRN LAKE MI/LOWER MI AREA THROUGH EARLY TONIGHT...
A PRONOUNCED MIDLEVEL LOW OVER THE UPPER MS VALLEY WILL CONTINUE TO
EJECT NEWD WHILE GRADUALLY EVOLVING INTO AN OPEN WAVE BY EARLY
TONIGHT. THE STRONGEST MIDLEVEL JET CORE WILL TRAVERSE NRN IL THIS
AFTERNOON AND LOWER MI THIS EVENING IN TANDEM WITH A DIFFUSE SURFACE
TROUGH/COLD FRONTAL SEGMENT AND AN ASSOCIATED BAND OF ASCENT. IN
ADVANCE OF THE SURFACE BOUNDARIES...BOUNDARY LAYER DEWPOINTS IN THE
MID 50S WILL SPREAD NWD/NEWD FROM IL/INDIANA INTO SRN LOWER MI THIS
AFTERNOON...WHILE A FEW CLOUD BREAKS WILL ALLOW SURFACE TEMPERATURES
TO WARM INTO THE LOW-MID 60S AS FAR N AS SRN LOWER MI. THE NET
RESULT WILL BE AN INCREASE IN MLCAPE TO 500-1000 J/KG BY MID-LATE
AFTERNOON FROM CENTRAL/NRN IL AND INDIANA INTO SRN LOWER MI.
IT APPEARS THAT THE STRONGEST FORCING FOR ASCENT WILL SPREAD NEWD
FROM WI TO UPPER MI AND NRN LOWER MI THIS AFTERNOON. HOWEVER...THE
SERN EXTENT OF THIS ASCENT WILL BRUSH THE NW EDGE OF THE
DESTABILIZING WARM SECTOR...AS EVIDENCED BY THE GRADUAL INCREASE IN
CONVECTION ACROSS NRN IL SINCE 15Z. PRESENT INDICATIONS ARE THAT
SOME FORM OF THIS IL CONVECTION WILL PERSIST INTO THE AFTERNOON
WHILE DEVELOPING NEWD TO EXTREME SE WI/SRN LAKE MI...AND EWD TOWARD
SRN LOWER MI. THE MODEST INSTABILITY WILL COMBINE WITH STRONG
DEEP-LAYER SHEAR /EFFECTIVE BULK SHEAR AOA 50 KT/ AND EFFECTIVE SRH
OF 150-250 M2/S2 TO SUPPORT A RISK FOR BOTH SUPERCELLS AND BOWING
SEGMENTS...WITH AN ATTENDANT RISK FOR DAMAGING WINDS AND A COUPLE OF
TORNADOES. THE PRIMARY SEVERE RISK IS EXPECTED TO BEGIN BY 21Z AND
PERSIST UNTIL ROUGHLY 03Z.
...MID SOUTH AND LOWER MS VALLEY AREA THROUGH EARLY TONIGHT...
SOMEWHAT NEBULOUS FLOW REGIME IS IN PLACE ACROSS THE LOWER MS VALLEY
AND MID SOUTH THIS MORNING...WITH WEAK-MODERATE SW FLOW ALOFT IN THE
WAKE OF THE DEPARTING UPPER MS VALLEY/GREAT LAKES TROUGH. A SUBTLE
EMBEDDED SPEED MAX IS PROGRESSING EWD OVER SE OK...AND WILL LIKELY
REACH THE MID SOUTH OVERNIGHT. FARTHER S...A WEAK SPEED MAX IS ALSO
MOVING OVER SRN LA.
A PERSISTENT CLUSTER OF STORMS NEAR LFT IS BEING MAINTAINED BY THE
WEAK SPEED MAX ALOFT...AS WELL AS LOW-LEVEL WAA ABOVE AN OUTFLOW
BOUNDARY TRAILING WWD FROM THE WEAKENING STORMS OVER THE WRN FL
PANHANDLE. A MARGINAL SEVERE RISK WILL CONTINUE WITH THIS
CONVECTION...CONSISTING PRIMARILY OF ISOLATED DAMAGING
WINDS/HAIL...BUT LOCALLY HEAVY RAINFALL SHOULD BE THE MORE
SIGNIFICANT CONCERN. FARTHER N...THE PATTERN IS MUDDLED BY OUTFLOW
FROM THE ONGOING STORMS ALONG THE I-10 CORRIDOR...WITH ONLY A
DIFFUSE CONFLUENCE ZONE TO FOCUS ADDITIONAL STORM DEVELOPMENT LATER
TODAY FROM NRN MS INTO WRN TN. MLCAPE COULD REACH 1500 J/KG IN AN
ENVIRONMENT WITH EFFECTIVE BULK SHEAR OF 25-30 KT...SUPPORTING SOME
RISK FOR LARGE HAIL AND/OR DAMAGING WINDS. WILL MAINTAIN A
CATEGORICAL OUTLOOK AREA TO COVER THESE THREATS...BUT THE OVERALL
SEVERE RISK APPEARS TO BE ON THE LOWER MARGINS FOR SLIGHT RISK.
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