SWODY1
SPC AC 210530
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 AM CDT SAT APR 21 2007
VALID 211200Z - 221200Z
..THERE IS A MDT RISK OF SVR TSTMS PORTIONS NWRN TX...CENTRAL/ERN
TX PANHANDLE...CENTRAL/ERN OK PANHANDLE...SWRN KS...
..THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM MN/ND BORDER
REGION TO WRN NEB TO PORTIONS W-CENTRAL TX...
..SYNOPSIS...
MAIN UPPER AIR FEATURE FOR THIS PERIOD WILL BE WELL-DEFINED LOW --
NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER SRN CA -- AND
ASSOCIATED SHORTWAVE TROUGH. THIS PERTURBATION WILL MOVE NEWD TO
CENTRAL PLAINS VICINITY KS/NEB BORDER BY 22/12Z. ASSOCIATED SFC
CYCLONE SHOULD DEVELOP WITHIN LEE TROUGHING OVER ERN CO...THEN MOVE
EWD OVER KS/NEB BORDER REGION OVERNIGHT. BAROCLINIC ZONE WILL
EXTEND NEWD FROM THIS LOW ACROSS WRN NEB...CENTRAL SD AND ERN ND
DURING AFTERNOON...BEFORE SHIFTING EWD TOWARD 22/12Z POSITION FROM
NWRN MN...ERN SD TO E-CENTRAL NEB. LATE AFTERNOON DRYLINE SHOULD
INTERSECT FRONTAL ZONE NE OF SFC LOW -- INVOF SWRN NEB OR EXTREME
NERN CO -- AND EXTEND SWD ACROSS OK/TX PANHANDLES.
..CENTRAL/SRN HIGH PLAINS NEAR DRYLINE...
BY MID-LATE AFTERNOON...SCATTERED-NUMEROUS TSTMS ARE EXPECTED TO
DEVELOP QUICKLY ALONG OR JUST E OF DRYLINE...WHICH WILL MARK SHARP
WRN GRADIENT OF BOTH CONVECTIVE AND SVR POTENTIAL. TORNADOES AND
DAMAGING GUSTS ARE POSSIBLE...ALONG WITH NUMEROUS REPORTS OF LARGE
HAIL. VERY LARGE/DAMAGING HAIL IS LIKELY WITH ANY DISCRETE
SUPERCELL.
DEEP-TROPOSPHERIC KINEMATIC PROFILES WILL STRENGTHEN THROUGHOUT
AFTERNOON/EVENING IN WARM SECTOR. BY 21-00Z...BOTH LOW LEVEL
HODOGRAPHS AND DEEP-LAYER BULK SHEAR WILL BECOME QUITE FAVORABLE FOR
SUPERCELLS...AS WELL FOR BOW/LEWP MODES IN ANY QUASI-LINEAR
CONVECTION THAT MAY EVOLVE SUBSEQUENTLY. WHILE TIMING OF THIS
TRANSITION REMAINS UNCERTAIN ATTM...DISCRETE STORMS SHOULD EVOLVE
INTO ONE OR MORE LINEAR BANDS AND SHIFT EWD OVER PORTIONS SWRN
NEB...WRN KS...ERN TX PANHANDLE...WRN OK AND PERHAPS W-CENTRAL TX.
EXPECT STRENGTHENING CAP WITH SWD EXTENT...SUCH THAT SVR
PROBABILITIES DIMINISH AND BECOME MORE CONDITIONAL OVER PERMIAN
BASIN REGION AND LOWER PECOS VALLEY. MEAN WIND VECTORS WILL BE LESS
PARALLEL TO DRYLINE S OF ROUGHLY I-40 THAN FARTHER N...INDICATING
SOMEWHAT GREATER AND LONGER LASTING POTENTIAL FOR DISCRETE
STRUCTURES. 45-55 KT EFFECTIVE SHEAR SHOULD BE COMMON.
A FEW POTENTIAL LIMITING FACTORS REMAIN APPARENT. LACK OF MORE
ROBUST PW IN GPS AND RAOB DATA UPSTREAM SUGGESTS FAVORABLE MID
50S-LOW 60S SFC DEW POINTS PRESENT DURING MORNING AND EARLY
AFTERNOON MAY AGAIN MIX OUT IN LARGE POCKETS...REDUCING THETAE IN
INFLOW LAYER FOR SOME TSTMS OVER THIS REGION. ALSO...CURRENT
SATELLITE TRENDS...AND PROGGED AND FCST MID/UPPER RH FIELDS SUGGEST
BAND OF THICK HIGH CLOUD COVER WILL OVERSPREAD MUCH OF THIS REGION
DURING AFTERNOON AND SLOW SFC HEATING. BACK EDGE OF THIS PLUME MAY
CLEAR DRYLINE AREA PRIOR TO 22/00Z. ALTHOUGH STRENGTH OF DEEP-LAYER
FORCING SUGGESTS CAP WILL WEAKEN AND TSTMS WILL DEVELOP ANYWAY
BEFORE 00Z...ACTIVITY MAY EXPAND IN COVERAGE QUITE RAPIDLY ONCE
INITIAL DEVELOPMENT DOES OCCUR. SVR POTENTIAL WILL TREND TOWARD
WIND/HAIL WITH EWD EXTENT AND SHOULD BECOME MORE MRGL THROUGH
OVERNIGHT HOURS.
..CENTRAL/NRN PLAINS NEAR FRONTAL ZONE...
SCATTERED-NUMEROUS TSTMS SHOULD DEVELOP INVOF SFC LOW OVER NERN CO
AND NEWD ALONG FRONTAL ZONE...WITH GREATEST POTENTIAL COVERAGE INVOF
THAT PORTION OF FRONT BETWEEN DRYLINE INTERSECTION AND SERN ND.
FCST VERTICAL SHEAR PROFILES FAVOR SUPERCELLS IN THIS REGION ALSO
WITH ENLARGED LOW LEVEL HODOGRAPHS...E.G. 0-3 KM SRH 200-300 J/KG.
DEEP-LAYER MEAN WINDS WILL BE NEARLY PARALLEL TO PRIMARY FORCING
BOUNDARY...SO EXPECT QUICK TRANSITION TO CLUSTERED/BANDED CONVECTIVE
ARRANGEMENT WITH TRAINING OF TSTMS POSSIBLE. BEFORE THAT
OCCURS...MAIN THREAT WILL BE LARGE/DAMAGING HAIL...WITH DAMAGING
GUSTS ALSO POSSIBLE. A FEW TORNADOES MAY OCCUR...ESPECIALLY IN
REGION OF RELATIVELY BACKED LOW LEVEL WINDS NEAR DRYLINE/FRONT
INTERSECTION. ONE OR MORE MCS MAY DEVELOP AND MOVE NEWD ACROSS THIS
REGION FROM LATE EVENING THROUGH OVERNIGHT HOURS AS WELL...AIDED BY
FAVORABLE WAA... MOISTURE TRANSPORT AND STORM-RELATIVE INFLOW ALONG
WRN PERIPHERY OF 45-55 KT LLJ. LARGE HAIL WOULD BE MAIN
THREAT...WITH OCNL DAMAGING WIND.
.EDWARDS/JEWELL.. 04/21/2007
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