SWODY1
SPC AC 260553
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1253 AM CDT SAT MAR 26 2011
VALID 261200Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS MID-SOUTH/LOWER MS
VALLEY REGIONS TO AL/GA...
...SYNOPSIS...
IN MID-UPPER LEVELS...SPLIT-FLOW PATTERN FCST TO CONTINUE ACROSS
CENTRAL/N-CENTRAL NORTH AMERICA...LEAVING MUCH OF CONUS IN BROAD
BELT OF NEARLY ZONAL FLOW. MID-UPPER LOW...NOW EVIDENT IN MOISTURE
CHANNEL IMAGERY OFFSHORE PAC NW -- IS FCST TO DEAMPLIFY TO OPEN-WAVE
TROUGH AND BECOME NEGATIVELY TILTED...WHILE MOVING INLAND WA/ORE.
SERN LOBE OF THIS PERTURBATION MAY REACH 4-CORNERS REGION BY END OF
PERIOD. MEANWHILE...SHORTWAVE TROUGH NOW CROSSING PORTIONS
CENTRAL/SRN ROCKIES IS FCST TO MOVE EWD ACROSS LOWER MO VALLEY
REGION TO LOWER OH VALLEY...AMPLIFYING AS IT ENTERS CONFLUENT FLOW
ASSOCIATED WITH CYCLONE OVER CANADIAN MARITIMES.
AT SFC...LOW NOW OVER SRN OK IS EXPECTED TO DEEPEN SOMEWHAT EARLY IN
PERIOD...AS SRN FRINGE OF MID-UPPER WAVE APCHS. FRONTAL ZONE -- NOW
EXTENDING FROM THAT LOW ESEWD ACROSS ARKLATEX REGION TO CENTRAL MS
-- IS FCST TO SHARPEN PARTIALLY FROM WEAK NONCONVECTIVE
FRONTOGENESIS...BUT MAINLY VIA REINFORCEMENT OF BAROCLINICITY BY
PRECIP TO ITS N. SFC LOW IS EXPECTED TO TRACK EWD ALONG FRONT TO
NERN LA/SERN AR/W-CENTRAL MS AREA BY 27/00Z...WHILE FRONT GENERALLY
LIFTS NWD ACROSS FOREGOING PORTIONS NRN MS AND CENTRAL/NRN AL.
TRAILING COLD FRONT BY THEN SHOULD EXTEND ACROSS NWRN LA...E TX AND
S-CENTRAL TX. BY END OF PERIOD...COLD FRONT SHOULD REACH
MIDDLE-UPPER TX COASTAL PLAIN AND CENTRAL MS...WITH LOW OVER
N-CENTRAL/NWRN GA.
...MID-SOUTH/LOWER MS VALLEY REGIONS TO AL/GA...
GREATEST POTENTIAL FOR SFC-BASED SVR TSTM DEVELOPMENT...INCLUDING
SUPERCELLS WITH TORNADOES...LARGE HAIL AND DAMAGING GUSTS...WILL BE
DURING MIDDAY THROUGH EARLY EVENING ACROSS CORRIDOR OF MAX
PROBABILITIES...ALONG AND S OF IMMEDIATE SFC FRONTAL ZONE. FRONT
SHOULD BE ALIGNED CLOSE TO MEAN WIND VECTOR...IN ENVIRONMENT
CHARACTERIZED BY INCREASING DIURNAL INSTABILITY...FAVORABLE
DEEP-LAYER SHEAR...AND ENHANCED HODOGRAPH SIZE/SRH ALONG BOUNDARY.
AS SUCH...ANY RELATIVELY DISCRETE STORMS THAT CAN INTERACT WITH
FRONT MAY SPEND A LONG TIME IN ITS VORTICITY-RICH ENVIRONMENT...WITH
ENHANCED TORNADO RISK.
MAIN UNCERTAINTY IS IN POSITION OF WARM/STATIONARY FRONT E OF LOW.
SOME LATITUDINAL MARGIN FOR ERROR IS NEEDED IN SVR PROBABILITIES
ATTM GIVEN WIDE VARIATION IN PROGGED TIMING/COVERAGE OF PRECIP N OF
FRONT...IN TURN INFLUENCING EFFECTIVE BOUNDARY LOCATION DURING PEAK
CONVECTIVE PERIOD. SCATTERED-NUMEROUS TSTMS IN CLUSTERS ARE
PROBABLE ACROSS PORTIONS AR AND MID-SOUTH DURING MORNING AND
AFTERNOON...CARRYING OVER FROM BEFORE 26/12Z. ADDITIONAL ACTIVITY
MAY FORM THROUGHOUT PERIOD N OF FRONT AS ELEVATED WAA/MOISTURE
TRANSPORT REGIME SHIFTS EWD ACROSS SRN APPALACHIANS.
S OF FRONTAL ZONE...IN ABSENCE OF APPRECIABLE MID-UPPER
PERTURBATIONS...CONVECTIVE INITIATION AND COVERAGE DEPEND ON
MESOSCALE SUBTLETIES AND CAPPING ISSUES NOT NECESSARILY WELL FCST BY
SYNOPTIC MODELS. VERTICAL SHEAR PROFILES CERTAINLY WILL BE
FAVORABLE FOR SUPERCELLS...HOWEVER...SO ANY CONVECTION THAT CAN
DEVELOP OVER CENTRAL/SRN PORTIONS AL...WRN GA AND MS S OF FRONT WILL
POSE TORNADO/HAIL/WIND THREAT AS WELL. CENTRAL/SRN AL MAY REPRESENT
RELATIVE MAX OF POTENTIAL S OF FRONT...SINCE IT WILL RESIDE E OF
STRONGEST ELEVATED MIXED LAYER AIR...WHERE CINH WILL BE WEAKENED
MOST READILY VIA AFTERNOON HEATING AND CONVECTIVE PROCESSES. SVR
PROBABILITIES SHOULD LESSEN WITH TIME AND EWD EXTENT ACROSS GA
OVERNIGHT AS INSTABILITY WEAKENS...BUT NOT DISAPPEAR ALTOGETHER.
UNCERTAINTIES REGARDING MORE PRECISE FRONTAL POSITION...BAND
COVERAGE S OF FRONT...PRECLUDE PROBABILITIES SUPPORTING CATEGORICAL
MDT RISK ATTM. HOWEVER...UPPER-END SLGT EASILY MAY BE UPGRADED ONCE
SOME OF THESE UNCERTAINTIES ARE BETTER RESOLVED.
...SERN KS/NERN OK TO WRN OZARK REGION...
ELEVATED CONVECTIVE REGIME AND RELATED HAIL POTENTIAL MAY CARRY OVER
FROM PREVIOUS DAY AND SHIFT EWD ACROSS THIS REGION...WITH HAIL BEING
POSSIBLE. LAPSE RATES AND BUOYANCY EACH SHOULD BE FAVORABLE DUE TO
COMBINATION OF RELATIVELY COLD AIR ALOFT AND NWRN LIMB OF LOW LEVEL
WARM/MOIST ADVECTION REGIME...CONTRIBUTING TO MUCAPE 1000-1500 J/KG.
WITH 50-60 KT EFFECTIVE SHEAR...TSTMS MAY BE SUFFICIENTLY ORGANIZED
FOR HAIL THREAT.
..EDWARDS/DEAN.. 03/26/2011
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