SWODY1
SPC AC 180532
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1232 AM CDT FRI APR 18 2008
VALID 181200Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS MS DELTA AND MIDDLE
GULF COAST REGIONS...
...SYNOPSIS...
IN MID-UPPER LEVELS...WRN NORTH ATLANTIC BLOCKING PATTERN WILL BREAK
DOWN AT LEAST TEMPORARILY...WITH INITIALLY LARGE CYCLONE OVER WRN
NORTH ATLANTIC EXPECTED TO WEAKEN AND EJECT NEWD. AS THIS
OCCURS...UPSTREAM CYCLONE NOW OVER KS IS FCST TO MOVE EWD...REACHING
VICINITY EXTREME SRN IL BY 19/12Z. ACCOMPANYING SHORTWAVE TROUGH
WILL ASSUME MORE NEUTRAL OR PERHAPS SOMEWHAT NEGATIVE TILT...AS
VORTICITY LOBE NOW OVER SERN NM AND FAR W TX PIVOTS EWD THROUGH BASE
OF SYSTEM.
CYCLONE CENTER ALOFT WILL BECOME MORE VERTICALLY JUXTAPOSED WITH SFC
LOW -- INITIALLY ANALYZED OVER NWRN MO. TRAILING SFC COLD FRONT
SHOULD CONTINUE TO SWEEP SEWD ACROSS TX BY 18/18Z...AND EWD ACROSS
AR..LA...MS AND PORTIONS TN/AL BY END OF PERIOD. FRONTOLYSIS IS
FORECAST DURING LATTER HALF OF PERIOD AS DEEP-LAYER CYCLONE
OCCLUDES/FILLS ACROSS MO/SRN IL.
...WRN GULF COASTAL PLAIN...MORNING...
NEAR-FRONTAL SQUALL LINE -- ALREADY WELL DEVELOPED AS OF THIS
WRITING FROM NEAR PRX-AUS-HDO -- WILL PROCEED ESEWD ACROSS ERN AND
S-CENTRAL/SERN TX...REACHING VICINITY TX/LA BORDER AND MID/UPPER TX
COASTAL PLAIN BY BEGINNING OF PERIOD. BY THAT TIME...RELATIVE
MINIMUM IN BOUNDARY LAYER INSTABILITY IS EXPECTED...THOUGH FCST
SOUNDINGS SUGGEST PRESENCE OF SFC DEW POINTS MID-UPPER 60S WITHIN
ABOUT 100 NM OF COAST WILL KEEP EFFECTIVE INFLOW PARCELS ROOTED AT
OR VERY NEAR SFC. STRONG COMPONENT OF MEAN FLOW ALOFT PARALLEL TO
BAND OF FORCING SUGGEST CONVECTIVE MODE WILL REMAIN LINEAR...PERHAPS
WITH OCCASIONAL LEWP/BOW STRUCTURES...SO MAIN CONCERN EARLY IN
PERIOD PRIMARILY WOULD BE A FEW STG-SVR CONVECTIVE GUSTS NEAR COAST.
...LOWER MS VALLEY/DELTA REGION TO TN VALLEY...
SCATTERED-NUMEROUS TSTMS MAY PERSIST OR REDEVELOP INVOF SFC FRONT
DURING LATE MORNING THROUGH AFTERNOON HOURS. EXPECT FAVORABLE
VERTICAL SHEAR ENVIRONMENT FOR SVR...AS APCHG SHORTWAVE TROUGH
INTENSIFIES GRADIENT FLOW ALOFT OVER WARM SECTOR. PREFRONTAL MOIST
AIR MASS IS FCST TO BE DIABATICALLY HEATED OVER LOWER DELTA REGION
DURING DAY...BOOSTING MLCAPES TO 1000-1500 J/KG OVER SRN PORTIONS OF
CATEGORICAL SLGT RISK AREA AND 500-1000 J/KG IN REMAINDER. STRENGTH
OF DEEP-LAYER WIND FIELDS AT ALL LEVELS ABOVE SFC...AS WELL AS
KINEMATIC GEOMETRY ALOFT WITH RESPECT TO PRIMARY ZONE OF CONVECTIVE
FORCING...SUGGEST WIND DAMAGE WILL BE PRIMARY CONCERN. HAIL
POTENTIAL IS MORE MRGL BECAUSE OF WEAK LAPSE RATES AND LIKELY
LINEARITY TO PREDOMINANT CONVECTIVE MODE. HOWEVER...ANY TSTMS THAT
MAY DEVELOP AHEAD OF LINE COULD ACQUIRE SUPERCELL CHARACTERISTICS
QUICKLY...WITH POTENTIAL FOR A FEW TORNADOES. AFTER DARK...OVERALL
SVR THREAT SHOULD DIMINISH WITH TIME AND SHRINK SEWD TOWARD AL/FL
PANHANDLE COAST.
FARTHER N...DIURNAL BUOYANCY PATTERN SHOULD BECOME MORE
FRAGMENTED...NARROWER...AND WEAKER IN MAGNITUDE WITH NWD EXTENT
BECAUSE OF LIMITING EFFECTS OF CLOUD COVER...AND PRESENCE OF LOWER
BOUNDARY LAYER THETAE. STILL...SOME SVR GUSTS OR SMALL HAIL CANNOT
BE RULED OUT WITH MOST INTENSE/EMBEDDED CELLS...AND A BRIEF
QLCS-TYPE TORNADIC SPINUP MAY OCCUR.
..EDWARDS/SMITH.. 04/18/2008
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