SPC AC 120545
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1245 AM CDT SUN APR 12 2009
VALID 131200Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER OH VALLEY TO NRN
FL...
...SYNOPSIS...
LARGE SCALE PATTERN CONTINUES TO LOOK FAVORABLE FOR SEVERE
THUNDERSTORM DEVELOPMENT ACROSS A GOOD PORTION OF THE U.S. FROM THE
LOWER OH VALLEY...SEWD INTO NRN FL MONDAY. IN ALL LIKELIHOOD A
BI-MODAL SCENARIO WILL EVOLVE WITH AN AXIS OF CONCENTRATED
THUNDERSTORM ACTIVITY AND TORNADOES EXPECTED ACROSS THE SRN GULF
STATES...WITH SECONDARY DEVELOPMENT BENEATH THE UPPER LOW FROM SERN
MO/ERN AR INTO SRN IL/IND/KY/TN.
...GULF STATES...
STRONG MID LEVEL FLOW...90KT SPEED MAX AT 500 MB...WILL OVERSPREAD
MUCH OF THE CNTRL GULF STATES EARLY IN THE PERIOD AS UPPER LOW MOVES
ACROSS THE CNTRL PLAINS INTO THE MID MS VALLEY REGION. THIS SHOULD
ENHANCE LOW LEVEL WARM ADVECTION IMMEDIATELY DOWNSTREAM AS LLJ
INCREASES IN EXCESS OF 60KT OVER AL/GA. NEEDLESS TO SAY SHEAR
PROFILES WILL STRONGLY SUPPORT STORM ORGANIZATION. IF DISCRETE
UPDRAFTS CAN EVOLVE THEN SUPERCELL STRUCTURES CAN BE
EXPECTED...HOWEVER A LARGE MCS MAY BE ONGOING AT THE BEGINNING OF
THE PERIOD...AN EXTENSION FROM OVERNIGHT ACTIVITY THAT WILL HAVE
SPREAD ACROSS THE LOWER MS VALLEY REGION. IT/S NOT ENTIRELY CLEAR
HOW FAR INLAND THE HIGHEST QUALITY MOISTURE WILL SURGE BEFORE
CONVECTIVE DEVELOPMENT OCCURS...EFFECTIVELY LOCKING IN MORE STABLE
BOUNDARY LAYER. MUCH OF THE NRN GULF REGION MAY STRUGGLE TO
DESTABILIZE SIGNIFICANTLY WITH MORE BUOYANT AIRMASS HOLDING ACROSS
SRN MS/AL/GA AND NRN FL. STRONG ISENTROPIC ASCENT SHOULD BE THE
PREDOMINANT FORCING MECHANISM FOR EARLY-MID DAY MCS AS IT PROPAGATES
DOWNSTREAM. WITH TIME STRONG HEATING WILL DEVELOP ALONG WRN/SRN
FRINGE OF THIS CONVECTIVE COMPLEX. STRONG THUNDERSTORMS SHOULD
REDEVELOP ALONG SWRN FLANK OF MCS AS SWLY LLJ SHOULD BE MAINTAINED
ACROSS THE NERN GULF OF MEXICO INTO FL PANHANDLE DURING THE
EVENING/OVERNIGHT HOURS. FORECAST SOUNDINGS BECOME QUITE IMPRESSIVE
DURING THE LATTER HALF OF THE PERIOD OVER THE NERN GULF COAST AS
FLOW INCREASES AHEAD OF MAIN UPPER TROUGH AXIS. LATEST THINKING IS
TORNADO THREAT MAY ACTUALLY INCREASE DURING THE LATTER HALF OF THE
PERIOD. SHEAR/INSTABILITY ALL FAVOR THE POTENTIAL FOR STRONG
TORNADOES...ESPECIALLY GIVEN THE LARGE SCALE SUPPORT THAT WILL
OVERSPREAD THIS REGION. AN UPGRADE TO MODERATE RISK MAY BE REQUIRED
IN LATER OUTLOOKS IF THIS SCENARIO CONTINUES TO BE FAVORED.
...MO/AR INTO SRN IL/IND/KY/TN...
VERY COLD MID LEVEL TEMPERATURES WILL OVERSPREAD THE MID MS VALLEY
REGION EARLY IN THE PERIOD WITH H5 VALUES ON THE ORDER OF -22C
OVERSPREADING SFC FRONTAL BOUNDARY...AND AT LEAST -20C A GOOD
100-150 MI AHEAD OF WIND SHIFT ALONG THE OH RIVER. STRONG BOUNDARY
LAYER HEATING WILL COMMENCE DURING THE MID-LATE MORNING HOURS WHICH
WILL ALLOW AIRMASS TO DESTABILIZE RAPIDLY BY 18Z FROM ERN AR/WRN TN
INTO SRN IL. SEVERE THUNDERSTORMS WITH HAIL SHOULD EVOLVE
ALONG/AHEAD OF COLD FRONT THEN SPREAD ENEWD AT ROUGHLY 30-35KT.
FORECAST SOUNDINGS SUPPORT SUPERCELL DEVELOPMENT AS A NARROW AXIS OF
LOWER 50S DEW POINTS SHOULD EASILY BE IN PLACE BY THIS TIME.
ALTHOUGH HAIL SHOULD BE THE PRIMARY THREAT...A FEW TORNADOES MAY
ALSO DEVELOP...ESPECIALLY BEFORE DARK.
..DARROW.. 04/12/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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