SWODY1
SPC AC 240559
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT FRI APR 24 2009
VALID 241200Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS WI/MI BORDER REGION TO NRN
KS...
...SYNOPSIS...
PRIMARY AND HIGHLY AMPLIFIED SHORTWAVE TROUGH IS EVIDENT ATTM FROM
HUDSON MAY REGION SWWD ACROSS SRN SASK...NRN ID AND ORE...THEN
OFFSHORE NRN CA. STG CONSENSUS OF OPERATIONAL GUIDANCE AND SREF
MEMBERS IS THAT SRN LOBE OF THIS PERTURBATION WILL DEVELOP CLOSED
500 MB LOW BY EARLY IN PERIOD OVER NRN CA...WHICH SHOULD MOVE SEWD
TO SWRN NV BY 25/12Z. ATTACHED SHORTWAVE TROUGH WILL MAINTAIN
PRONOUNCED POSITIVE TILT. SRN STREAM SHORTWAVE TROUGH -- NOW
EVIDENT IN MOISTURE CHANNEL IMAGERY AND VWP/PROFILER DATA OVER W TX
-- IS FCST TO MOVE EWD OVER E TX AND AR LATE IN PERIOD...WHILE
WEAKENING. AT SFC...COLD FRONT IS FCST TO SAG SWD ACROSS UPPER MS
VALLEY AND CENTRAL PLAINS.
...WI/MI BORDER REGION TO NRN KS...
SCATTERED TSTMS SHOULD DEVELOP INVOF SFC FRONT DURING AFTERNOON AND
EVENING...PERHAPS IN A FEW LOOSELY SEGMENTED NODES AT FIRST...THEN
CONGEALING INTO MORE CONTINUOUS BAND OF ACTIVITY WITH EMBEDDED
STG-SVR TSTMS BY EARLY EVENING. EVENTUAL QUASI-LINEAR MODE IS
EXPECTED TO EVOLVE...GIVEN KINEMATIC GEOMETRY RELATIVE TO FRONTAL
ZONE. LONG FETCH OF SWLY FLOW ALOFT IS FCST DOWNSTREAM FROM
MID-UPPER LOW OVER CA/NV...AND SHOULD BLOW NEARLY PARALLEL TO SFC
FRONTAL ZONE BETWEEN UPPER GREAT LAKES AND CENTRAL PLAINS. EXPECT
SFC DEW POINTS GENERALLY MID 50S TO LOW 60S F -- BELOW MID 60S
UNREASONABLY PROGGED BY NAM-BKF -- WILL CONTRIBUTE TO MLCAPE
2000-2500 J/KG OVER MUCH OF THIS CORRIDOR.
CONVECTIVE COVERAGE SHOULD BECOME SMALLER ACROSS KS...WHERE STRONGER
CAP BUT ALSO STRONGER HEATING AND STEEPER LOW-MIDLEVEL LAPSE RATES
WILL RESULT IN MORE SPORADIC/CONDITIONAL SVR THREAT...BUT RISK OF
SIGNIFICANT SEVERE HAIL WITH ANY SUPERCELLS. VERTICAL SHEAR PROFILES
WILL BE FAVORABLE FOR STORM ROTATION -- WITH ATTENDANT RISK OF LARGE
AND DAMAGING WIND -- THROUGHOUT CATEGORICAL OUTLOOK AREA.
SUPERCELLS ARE MOST LIKELY WITH ANY RELATIVELY SUSTAINED/DISCRETE
STORMS WHOSE INFLOW AND PRECIP DISTRIBUTION IS NOT DISRUPTED BY
OTHER CONVECTION IN CLOSE PROXIMITY. SVR POTENTIAL SHOULD DIMINISH
AFTER APPROXIMATELY 06Z AS NOCTURNALLY COOLED BOUNDARY LAYER
DEEPENS...AND AS PREFRONTAL LLJ BECOMES MORE PARALLEL WITH FRONTAL
ZONE.
...CENTRAL/E TX...
SEVERAL CLUSTERS OF TSTMS SHOULD DEVELOP THROUGHOUT PERIOD IN ZONE
OF CYCLONIC MID-UPPER FLOW...LARGE-SCALE ASCENT/DESTABILIZATION
ALOFT...AND FAVORABLE LOW LEVEL MOISTURE SURROUNDING UPPER TROUGH.
POCKETS OF STG SFC HEATING...DIFFERENTIAL HEATING ZONES AND/OR
OUTFLOW BOUNDARIES APPEAR TO BE LIKELIEST SOURCES OF SUFFICIENT LOW
LEVEL LIFT. HOWEVER...STRENGTH/POSITION OF SUCH BOUNDARIES REMAINS
STRONGLY DEPENDENT ON MESOBETA SCALE FACTORS AND THUS VERY UNCERTAIN
ATTM.
DURING AFTERNOON...WHEN CONVECTION SHOULD BE STRONGEST
OVERALL...ENHANCED DEEP-LAYER SHEAR MAY EXIST BENEATH BELT OF
STRONGEST 700-500 MB WINDS...FROM BASE OF TROUGH OVER S-CENTRAL TX
NEWD ACROSS COASTAL PLAIN TO SE TX. GREATER CAPPING OVER THIS
AREA...AND LACK OF EVIDENT BOUNDARIES AS INITIATING FOCI...LEND
UNCERTAINTY TO COVERAGE OF CONVECTION. FARTHER N TOWARD ARKLATEX
AND N-CENTRAL TX...FLOW SHOULD BE MORE UNIDIRECTIONAL...WITH WEAKER
CAPPING BUT ALSO CONCERNS OVER CLOUD COVER AND PRECIP LIMITING
BOUNDARY LAYER DESTABILIZATION. GIVEN THESE OFFSETTING
FACTORS....WILL MAINTAIN BROAD-BRUSH AREA OF MRGL SVR PROBABILITIES
ATTM...AWAITING BETTER DEFINED/JUXTAPOSED MESOSCALE FOCI BEFORE
PERFORMING ANY CATEGORICAL UPGRADE.
...CAROLINAS TO ERN GA...
WIDELY SCATTERED TO SCATTERED TSTMS MAY DEVELOP DURING AFTERNOON IN
ZONE OF STG SFC HEATING AND PROGRESSIVELY WEAKER CINH...PERHAPS
REGULATED OVER SRN PORTION OF OUTLOOK BY BOUNDARY LEFT BEHIND FROM
PRIOR GA ACTIVITY. SFC DEW POINTS MID 50S TO LOW 60S F BENEATH 7-8
DEG C/KM LOW-MIDLEVEL LAPSE RATES WILL CONTRIBUTE TO MLCAPE
1500-2500 J/KG ATOP WELL-MIXED/SUBCLOUD LAYER. POTENTIALLY DAMAGING
GUSTS APCHG 50 KT SVR CRITERIA...AS WELL AS ISOLATED MRGL SVR
HAIL...ARE POSSIBLE. GIVEN POSITION OF THIS REGION ALMOST DIRECTLY
BENEATH MID-UPPER LEVEL HIGH...FLOW WILL BE WEAK AT ALL LEVELS...AS
WILL VERTICAL SHEAR. THIS WILL LIMIT STORM MODE TO MULTICELLULAR
AND PULSE IN CHARACTER...AND DAMPEN OVERALL ORGANIZATION OF SVR
THREAT.
..EDWARDS.. 04/24/2009
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