SWODY1
SPC AC 160543
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1143 PM CST FRI FEB 15 2008
VALID 161200Z - 171200Z
..THERE IS A MDT RISK OF SVR TSTMS PORTIONS S-CENTRAL
TX...MID/UPPER TX COASTAL PLAIN...TO E-CENTRAL TX...
..THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM PORTIONS
W-CENTRAL/SW TX TO LOWER TX COAST...ARKLATEX REGION...MUCH OF
LA...AND WRN MS....
OUTBREAK OF SVR TSTMS -- PERHAPS INCLUDING SUPERCELLS WITH
SIGNIFICANT TORNADOES -- APPEARS MOST PROBABLE FROM S-CENTRAL TX
ACROSS COASTAL PLAIN INTO E TX DURING AFTERNOON AND EVENING.
DAMAGING CONVECTIVE WINDS SHOULD BE COMMON WITH THIS SYSTEM...AND
NUMEROUS REPORTS OF LARGE HAIL ALSO MAY OCCUR.
..SYNOPSIS...
MAIN UPPER AIR FEATURE FOR THIS FCST PERIOD WILL BE UPPER LOW -- NOW
EVIDENT IN MOISTURE CHANNEL IMAGERY OVER EXTREME SERN AZ. THIS
CYCLONE IS FCST TO MOVE EWD ACROSS LOWER PECOS VALLEY BEFORE TURNING
NEWD OVER ERN OK LATE IN PERIOD..IN RESPONSE TO APPROACH OF
SHORTWAVE TROUGH NOW DIGGING SEWD ACROSS PACIFIC NW.
AT SFC...COMPLEX PATTERN SHOWS THREE MAIN FEATURES ATTM...
1. ARCTIC FRONTAL ZONE -- ANALYZED INITIALLY FROM ARKLATEX REGION
SWWD ACROSS CLL/SAT AREAS TO FRONTAL-WAVE CYCLONE BETWEEN
COT-DRT...THEN SWWD INTO MOUNTAINS OF CENTRAL COAHUILA. THIS FRONT
IS FCST TO PIVOT CYCLONICALLY EARLY IN PERIOD...MOVING SEWD ACROSS
RIO GRANDE VALLEY WHILE RETREATING SLIGHTLY NWWD OVER CENTRAL/N TX.
THIS WILL OCCUR AS LEESIDE LOW -- INITIALLY OVER NERN
MEX...MOVES/REFORMS NEWD OVER N-CENTRAL TX. BY 17/00-03Z TIME
FRAME...WELL-DEFINED SFC LOW SHOULD BE OVER SERN OK WITH FRONT
MOVING EWD/SEWD OVER E-CENTRAL TX AND COASTAL BEND REGION. BY
17/12Z...EXPECT OCCLUDED/STACKED CYCLONE FROM SFC-500 MB OVER MO
OZARKS...COLD FRONT SWD ACROSS LA AND NWRN GULF.
2. DRYLINE...DIFFICULT TO LOCATE PRECISELY ATTM BUT EVIDENT OVER
PIEDMONT REGION BETWEEN MEX SERRANIAS DEL BURRO RANGE AND RIO
GRANDE. THIS FEATURE MAY MOVE E OF RIO GRANDE THROUGH EARLY-MID
AFTERNOON...OVER PORTIONS DEEP S TX...BEFORE BEING OVERTAKEN BY COLD
FRONT.
3. MARINE WARM FRONT...ANALYZED INITIALLY FROM ABOUT 125 SSW
MSY...JUST S OF GLS...TO FAYETTE COUNTY TX...INTERSECTING ARCTIC
BOUNDARY ABOUT 40 NNE VCT. THIS DENOTES NRN EDGE OF HIGH THETAE
GULF AIR WITH DEW POINTS UPPER 60S TO LOW 70S F. WARM FRONT SHOULD
LIFT NWD ACROSS CENTRAL AND SE TX FASTER THAN OVER SWRN LA. THIS
WILL CAUSE TRIANGULAR WEDGE OF RICHEST WARM SECTOR AIR TO LIFT NWD
ACROSS E TX BEFORE COLD FROPA. WARM SECTOR EXPANSION FARTHER NE
OVER LA AND ARKLATEX REGION PROBABLY WILL BE IMPEDED/PREVENTED BY
CLOUDS AND PRECIP.
..S-CENTRAL TX TO SWRN LA...WARM SECTOR...
GREATEST COVERAGE OF TSTMS IS FCST INVOF COLD FRONT WHERE LINEAR
EVOLUTION SHOULD TAKE PLACE...CHARACTERIZED BY SWWD BACKBUILDING
WITH TIME. EMBEDDED SUPERCELLS/BOWS WILL POSE RISK OF BOTH DAMAGING
WIND AND TORNADOES...ALONG WITH HAIL. TRANSITION OF INFLOW PARCELS
FROM SFC-BASED TO ELEVATED MAY BE GRADUAL AND NEBULOUS ACROSS
DIFFUSE WARM FRONTAL ZONE...SO TORNADO/WIND PROBABILITIES ARE DRAWN
TO ALLOW CONSIDERABLE NWD TOLERANCE FOR WARM SECTOR EXPANSION OVER E
TX.
POTENTIAL FOR RELATIVELY DISCRETE/ROTATING TSTMS WILL BE GREATEST
ALONG SWRN/TAIL END OF CONVECTIVE BAND...WHERE BOUNDARY LAYER INFLOW
IS MOST UNDISTURBED AND AVAILABLE BUOYANCY RELATIVELY MAXIMIZED.
SUCH TSTMS...AS WELL AS ANY RELATIVELY DISCRETE WARM SECTOR
CONVECTION...MAY PRODUCE STRONG TORNADOES. EXPECT INFLOW
ENVIRONMENT OF RICH MOISTURE...LOW LCL...50-60 KT EFFECTIVE
SHEAR...AND VERY LARGE HODOGRAPHS WITH 0-1 KM SRH COMMONLY ABOVE 350
J/KG.
MAIN UNCERTAINTIES ATTM INVOLVE INITIATION AND COVERAGE OF ANY
SUSTAINED CONVECTION S OF FRONT...AND ALONG OR E OF POSSIBLE
DRYLINE. PLUME OF ELEVATED MIXED-LAYER AIR WILL REMAIN OVER MUCH OF
THIS REGION THROUGHOUT DAYLIGHT HOURS...ENHANCING LAPSE RATES AND
CAPE...BUT ALSO SUPPORTING POTENTIAL FOR CAPPING TO SUPPRESS
PREFRONTAL DEVELOPMENT. LATE IN PERIOD...GREATEST SVR POTENTIAL
SHOULD SHRINK SEWD IN AREAL EXTENT ACROSS LA...AND DIMINISH SOMEWHAT
IN MAGNITUDE...DURING OVERNIGHT HOURS. HOWEVER...DEEP-LAYER SHEAR
PROFILES STILL WILL SUPPORT SOME SUPERCELL/BOW POTENTIAL OVER WARM
SECTOR.
..W-CENTRAL/NW TX...NW OF ARCTIC FRONT...
SCATTERED TSTMS WITH POTENTIAL FOR ISOLATED HAIL SHOULD BE ONGOING
AT BEGINNING OF PERIOD ACROSS PORTIONS W-CENTRAL/NW TX. FARTHER
W...LEADING EDGE OF STRONGEST MID/UPPER LEVEL ASCENT SHOULD MOVE
INTO W-CENTRAL TX AROUND BEGINNING OF PERIOD...BECOMING INCREASINGLY
JUXTAPOSED WITH WRN PORTIONS OF ELEVATED WAA AND MOIST ADVECTION
REGIME IN LOW LEVELS. THIS SHOULD RESULT IN ADDITIONAL TSTMS IN
GENERALLY N-S ALIGNED BAND...SHIFTING EWD ACROSS THIS REGION.
FAVORABLE LAPSE RATES AND LOW LEVEL THETAE WILL EXIST TO SUPPORT
SOME MUCAPE VALUES 500-1000 J/KG...AMIDST FAVORABLE EFFECTIVE SHEAR
FOR ORGANIZED CONVECTION. ALTHOUGH LINEAR MODE SHOULD
PREDOMINATE...HAIL MAY OCCUR FROM SOME OF THIS ACTIVITY.
..ARKLATEX REGION...
NRN SEGMENT OF FRONTAL CONVECTIVE BAND -- N OF MARINE BOUNDARY --
MAY PRODUCE LARGE HAIL AND STG GUSTS AS IT MOVES INTO SLIGHTLY
ELEVATED PLUME OF FAVORABLE BUOYANCY OVER SERN OK...SRN
AR...PORTIONS NRN/NERN LA AND EXTREME NE TX. ALTHOUGH LAPSE RATES
ALOFT MAY BE WEAKER THAN FARTHER W...RICH LOW LEVEL MOISTURE SHOULD
CONTRIBUTE TO MUCAPES UP TO 1000 J/KG...WITH 45-55 KT EFFECTIVE
SHEAR.
.EDWARDS/HURLBUT.. 02/16/2008
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