SWODY3
SPC AC 300730
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 AM CDT WED APR 30 2008
VALID 021200Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS LOWER MS VALLEY REGION TO LOWER
MI AND SRN WI...
...SYNOPSIS...
LARGE MID/UPPER LEVEL CYCLONE -- NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY AND RAOB ANALYSES OVER BC AND PACIFIC NW -- IS FCST TO
REDEVELOP SEWD TO NEB DAY-2. CYCLONE THEN SHOULD OCCLUDE IN
LOW-MIDDLE LEVELS...FOLLOWED BY AT LEAST PARTIAL MERGER/PHASING WITH
TROUGH EXTENDING SWD FROM UPPER LOW OVER HUDSON BAY. LATER PROCESS
IS HANDLED WITH GREAT INCONSISTENCY BOTH BETWEEN OPERATIONAL MODELS
AND AMONG INDIVIDUAL SREF MEMBERS...WITH 500 MB LOW PROGGED ANYWHERE
BETWEEN WRN MO AND SWRN LS IN THOSE PROGS THAT MAINTAIN CLOSED
CYCLONE. SEVERAL ENSEMBLE MEMBERS -- INCLUDING AT LEAST ONE FROM
EACH MODEL TYPE -- PROG MORE COMPLETE PHASING WITH NRN SYSTEM...I.E.
NO MORE CLOSED LOW...AND VARYING POSITIONS/TILTS TO RESULTANT
OPEN-WAVE TROUGHING OVER MID/UPPER MS VALLEY REGION BY 3/12Z.
PROGGED DISCREPANCIES IN SFC FEATURES ARE LESS PRONOUNCED...SUCH
THAT BY 3/00Z...WARM/COLD FRONTAL TRIPLE-POINT LOW SHOULD BE LOCATED
BETWEEN ERN IA-ERN WI...E OR SE OF OLDER/OCCLUDED CYCLONE. COLD
FRONT SHOULD EXTEND SSWWD ACROSS IL...ARKLATEX REGION AND S-CENTRAL
TX.
...LOWER MS VALLEY REGION TO LOWER MI AND SRN WI...
TREMENDOUS SPREAD IN PROGS REGARDING PHASING OF CANADIAN AND CENTRAL
CONUS UPPER SYSTEMS RESULTS IN CORRESPONDINGLY LARGE VARIETY OF
POSSIBLE MASS FIELD ADJUSTMENTS AND KINEMATIC GEOMETRIES ALOFT.
THIS CREATES CONSIDERABLE UNCERTAINTIES IN FCST OF CONVECTIVE
TIMING/EVOLUTION...EVEN GIVEN TIGHTER CLUSTERING OF SFC GUIDANCE.
IN GENERAL...PRIND BAND OF TSTMS SHOULD EXIST AT BEGINNING OF PERIOD
ALONG OR JUST AHEAD OF SFC COLD FRONT FROM UPPER MS VALLEY REGION
SWWD AT LEAST INTO AR...WITH DAMAGING WIND...OCCASIONAL HAIL AND
PERHAPS A FEW TORNADOES POSSIBLE. SVR POTENTIAL EARLY IN PERIOD MAY
EXTEND AS FAR SW AS CENTRAL TX...BUT SEVERAL CONCERNS PRECLUDE
CATEGORICAL OUTLOOK FOR THAT PORTION OF FRONTAL ZONE ATTM. ALTHOUGH
MOISTURE WILL BE RICHEST FROM ARKLATEX REGION SWD...OFFSETTING
FACTORS MAY INCLUDE CAPPING...WEAK UPPER LEVEL SUPPORT...AND LACK OF
STRONGER CONVERGENCE BECAUSE OF SOMEWHAT VEERED/WEAKER WINDS IN
ADJACENT WARM SECTOR. THIS SUGGESTS LESSER EARLY-PERIOD CONVECTIVE
COVERAGE AND MORE CONDITIONAL SVR POTENTIAL.
ADDITIONAL DEVELOPMENT IS POSSIBLE ALONG/AHEAD OF SFC COLD FRONT
DURING DAY...FROM IL/INDIANA AND PERHAPS SRN LM AREA SWWD ACROSS
LOWER MS VALLEY. STRONGER DEEP-LAYER WINDS SHOULD EXIST OVER NRN
PARTS OF OUTLOOK AREA...WITH LAPSE RATES...LOW LEVEL MOISTURE AND
BUOYANCY INCREASING SWD. DEEP-LAYER SHEAR PROFILES WILL SUPPORT
SUPERCELL/TORNADO THREAT WITH ANY RELATIVELY DISCRETE/SUSTAINED
CONVECTION...AND DAMAGING WIND THREAT WOULD DOMINATE WITH MORE
LINEAR ACTIVITY. ONE OR TWO RELATIVELY SMALL AREAS OF CONCENTRATED
AND/OR SIGNIFICANT SVR POTENTIAL ARE QUITE POSSIBLE WITHIN CURRENT
BROAD-BRUSHED CATEGORICAL AREA. HOWEVER...AFOREMENTIONED
UNCERTAINTIES PRECLUDE FOCUSING SUCH PROBABILITIES ON ANY PARTICULAR
AREA WITHIN SLGT RISK THIS FAR IN ADVANCE.
..EDWARDS.. 04/30/2008
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