SWODY1
SPC AC 220059
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 PM CDT THU APR 21 2011
VALID 220100Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SW TX TO SWRN OK...
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NERN OK/KS/AR/MO...
...SYNOPSIS...
BROAD AREA OF CYCLONIC FLOW OVER NWRN CONUS IS ASSOCIATED WITH TWO
SHORTWAVE TROUGHS...
1. STRONGER PERTURBATION MOVING SLOWLY EWD ACROSS ERN PORTIONS
WA/ORE TOWARD ID...AND
2. LEADING/SRN TROUGH NOW APPARENT IN MOISTURE CHANNEL IMAGERY AND
VWP/RAOB DATA OVER UT.
AS HEIGHTS FALL TO ITS NW...LEADING TROUGH WILL MOVE EWD ACROSS
CENTRAL ROCKIES TO ERN WY...BLACK HILLS AND NEB PANHANDLE REGION.
BY 12Z...LOW-AMPLITUDE TROUGHING...WITHOUT SIGNIFICANT VORTICITY
CONCENTRATIONS...SHOULD EXTEND SWD ACROSS NM AND FAR W TX.
AT SFC...QUASISTATIONARY FRONT WAS ANALYZED AT 23Z FROM SEA BREEZE
INTERSECTION OVER SERN GA WWD OVER SRN AL...BECOMING DIFFUSED BY
OUTFLOW FROM EARLIER CONVECTION OVER SRN PORTIONS MS/AL. BOUNDARY
THEN BECAME BETTER-DEFINED AGAIN AS WARM FRONT ACROSS EXTREME NRN
LA...NE TX...JUST N OF DFW METROPLEX...THEN WSWWD TO JUST N ABI.
FRONT MERGED WITH DRYLINE NEAR SERN LYNN COUNTY TX. BLENDED WARM
FRONT/DRYLINE EXTENDED NWD ACROSS WRN SOUTH-PLAINS OF TX AND WRN
PANHANDLE TO SFC LOW OVER SERN CO. SECONDARY/FRONTOGENETIC ZONE WAS
EVIDENT FROM NEAR ADM WNWWD NEAR LTS...THEN NWWD ACROSS N-CENTRAL
PORTIONS TX PANHANDLE. EXCEPT WHERE LOCALLY MODULATED BY
OUTFLOW...SRN BOUNDARY SHOULD WEAKEN OVERNIGHT BENEATH STG LOW-LEVEL
WAA...WHILE PRIMARY SYNOPTIC WARM FRONT DEVELOPS NWD INTO PORTIONS
SRN/CENTRAL KS. LOW SHOULD MOVE EWD ACROSS SWRN KS/NRN OK AREA.
DRYLINE...ANALYZED FROM NWRN COAHUILA NEAR FST THEN NNEWD TO
FRONT...SHOULD RETREAT SLIGHTLY NWWD ACROSS PORTIONS PERMIAN BASIN.
...NERN OK/KS/AR/MO...
LARGE COMPLEX OF MAINLY NON-SEVERE CONVECTION IS MOVING NEWD ACROSS
OZARKS REGION ATTM...ALTHOUGH OCNL SVR HAIL CANNOT BE RULED OUT FROM
CORES ALONG ITS SRN/WRN FRINGES WHERE ACCESS TO MOST
BUOYANT/ELEVATED INFLOW WILL REMAIN. REF SPC WW 175 AND
ACCOMPANYING MESOSCALE DISCUSSIONS FOR NEAR-TERM GUIDANCE.
OVERNIGHT...EXPECT COMBINATION OF HEIGHT FALLS...STRENGTHENING
DEEP-LAYER SHEAR...AND INCREASING WAA/MOISTURE TRANSPORT INTO NRN
PARTS OF THIS REGION...AHEAD OF APCHG SHORTWAVE TROUGH. AS THIS
OCCURS...ELEVATED WARM FRONTOGENETIC FORCING AND ISENTROPIC ASCENT
TO LFC EACH SHOULD STRENGTHEN AS WELL...WITH CORRESPONDING
DEVELOPMENT/INCREASE IN COVERAGE/INTENSITY OF TSTMS OVER LOWER MO
VALLEY REGION.
...SW TX TO SWRN OK...
SEVERAL STG-SVR TSTMS...INCLUDING A FEW SUPERCELLS CAPABLE OF VARY
LARGE/DAMAGING HAIL AND TRANSIENT TORNADOES...ARE APPARENT E OF
DRYLINE OVER WW 176. OPTIMAL COMBINATION OF BUOYANCY AND SHEAR
SHOULD REMAIN INVOF WARM-FRONTAL ZONE FROM SNK/ABI AREAS EWD TOWARD
SEP/MWL AREA...ALONG WITH EFFECTIVE SRH AND LOW-LEVEL VORTICITY IN
SUPPORT OF SUPERCELLS. INCREASING CAPPING WITH TIME...PER MODIFIED
00Z FWD/DRT RAOBS FOR SFC COOLING...CASTS SOME UNCERTAINTY ON HOW
FAR E ACTIVITY CAN PERSIST ACROSS/BEYOND WW AREA. SRN COMPLEX MAY
GROW UPSCALE SUFFICIENTLY TO ORGANIZE COLD POOL AND PERSIST ACROSS
PORTIONS EDWARDS PLATEAU/SWRN HILL COUNTRY. SEE WW AND ATTENDANT
MESOSCALE DISCUSSIONS FOR NOWCAST INFORMATION ON SVR THREAT IN THIS
REGION.
MODIFIED RAOBS AND FCST SOUNDINGS SUGGEST ENVIRONMENT SUPPORTING
ELEVATED SUPERCELLS AND LARGE HAIL POTENTIAL N OF SFC FRONT THROUGH
MUCH OF TONIGHT...MAIN UNCERTAINTIES INVOLVING INITIATION AND
COVERAGE. CONVECTION NEAR TRIPLE POINT MAY MOVE ALONG OR N OF FRONT
AS FRONT LIFTS NWD...AND/OR ADDITIONAL TSTMS MAY DEVELOP N OF FRONT.
HODOGRAPHS APPEAR RATHER LARGE AND CURVED FOR SUSTAINED
LEFT-SPLITS...AND ARE FCST TO GROW BIGGER OVERNIGHT AS LLJ
STRENGTHENS TO 40-50 KT RANGE. HOWEVER...PARCELS N OF WHAT NOW IS
PRIMARY WARM FRONT SHOULD REMAIN ROOTED ABOVE SFC...WITH LARGE HAIL
BEING MAIN THREAT FROM ANY TSTMS AFTER ABOUT 06Z.
...CENTRAL HIGH PLAINS...
ISOLATED STG-SVR GUSTS ARE STILL POSSIBLE FOR ANOTHER COUPLE OF
HOURS FROM HIGH-BASED CONVECTION MOVING OVER DEEPLY WELL-MIXED
BOUNDARY LAYER. HOWEVER...LARGE DEWPOINT DEPRESSIONS AT SFC WILL
CONTRIBUTE TO SHARP DIABATIC COOLING/STABILIZATION AND WEAKENING OF
WIND THREAT THIS EVENING.
..EDWARDS.. 04/22/2011
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