SWODY1
SPC AC 040600
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT THU OCT 04 2007
VALID 041200Z - 051200Z
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NERN NEB...ERN
SD...SWRN MN...NWRN IA...
..SYNOPSIS...
UPPER AIR PATTERN FCST TO AMPLIFY ACROSS MUCH OF CONUS THIS
PERIOD...RELATED LARGELY TO STRENGTHENING OF MEAN TROUGH ACROSS WRN
STATES. SPEED MAX ALOFT -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
OFFSHORE ORE -- SHOULD DIG SWD IN CONCURRENCE WITH STRONG HEIGHT
FALLS DOWNSTREAM OVER PACIFIC COAST STATES. SEVERAL PROGS INDICATE
THAT RESULTANT CLOSED LOW -- FCST OVER NRN CA AND ORE BY 5/12Z --
WILL HAVE AT LEAST TWO VORTICITY/CIRCULATION CENTERS...WITH AT LEAST
150 KT 250 MB JET MAX STILL OFFSHORE AND W OF TROUGH BY END OF
PERIOD. DOWNSTREAM...BROAD FETCH OF SWLY FLOW WILL COVER MUCH OF
ROCKIES AND GREAT PLAINS...GENERALLY STRENGTHENING WITH NWD EXTENT
ACROSS NEB/DAKOTAS. BY 5/00Z...EXPECT 140-160 KT 250 MB FLOW CORE
ACROSS SRN SASK/MB...AND SECONDARY/WEAKER MAX OF 70-90 KT FROM SWRN
AZ TO NWRN KS. SRN STREAM PERTURBATION INITIALLY OFFSHORE NRN BAJA
IS EXPECTED TO EJECT NEWD ACROSS WRN/CENTRAL AZ THIS AFTERNOON AS
POSITIVELY TILTED SHORTWAVE TROUGH.
SFC BAROCLINIC ZONE NOW ANALYZED FROM W-CENTRAL TX TO CENTRAL OK AND
WRN OZARKS WILL MOVE NWD AND BECOME PROGRESSIVELY MORE DIFFUSE
THROUGH PERIOD. MEANWHILE...LEESIDE CYCLOGENESIS IS FCST OVER NERN
WY/SERN MT...WITH WARM FRONTOGENESIS EWD ACROSS NERN NEB/SRN SD.
RESULTING WARM FRONT SHOULD LIFT NWD OVER SD...WHILE LEE TROUGH
EXTENDS FROM N-CENTRAL NEB/S-CENTRAL SD SSWWD ACROSS ERN KS AND W
TX. DRYLINE SHOULD BE NEARLY COLOCATED WITH LEE TROUGH...AND SHOULD
BECOME BETTER DEFINED FROM S-N THROUGH AFTERNOON/EVENING AS MOISTURE
ADVECTS NWD ACROSS CENTRAL PLAINS.
..NRN PLAINS/UPPER MIDWEST...
CONDITIONAL POTENTIAL FOR DIURNAL/SFC-BASED CONVECTIVE DEVELOPMENT
EXISTS INVOF SFC WARM FRONT AND ALONG/AHEAD OF LEE TROUGH/DRYLINE.
VERTICAL SHEAR PROFILES...PARTICULARLY ALONG WARM FRONT WHERE SFC
FLOW WILL BE BACKED -- WILL BE FAVORABLE FOR SUPERCELLS WITH HAIL
AND WIND DAMAGE POTENTIAL. ETA-KF AND WRF FCST HODOGRAPHS YIELD
100--150 J/KG OF 0-1 KM SRH...ALTHOUGH LACK OF MORE INTENSE MIDLEVEL
WINDS RESULTS IN ONLY 30-35 KT EFFECTIVE BULK SHEAR VALUES. MAIN
QUESTION IS TIMING/VIGOR OF ARRIVAL OF MOST FAVORABLE MOISTURE
RETURN. SRN PLAINS FRONTOLYSIS WILL LEAD TO MERIDIONAL DEFORMATION
AND NWD MOVEMENT OF PLUME OF MOIST LOW LEVEL AIR NOW CHARACTERIZED
BY 70S F SFC DEW POINTS OVER SRN/ERN OK AND MID/UPPER 60S OVER SWRN
OK...N TX AND AR. ARRIVAL OF NRN PORTION OF THIS AIR MASS INVOF
WARM FRONT BEFORE 5/00Z MAY COMBINE WITH WEAK WARM FRONTAL LIFT AND
SFC HEATING TO WEAKEN CAP ENOUGH FOR INITIATION.
MORE CONFIDENCE EXISTS IN EVENING/OVERNIGHT INITIATION ALONG AND N
OF WARM FRONT FROM SIOUX-LAND AREA NEWD INTO SRN MN...ALONG AND W OF
NOSE OF INCREASINGLY MOIST/30-40 KT SSWLY LLJ. ACTIVITY SHOULD
SPREAD/SHIFTING OVER ERN MN AND WRN WI BEFORE END OF PERIOD...WITH
LARGE HAIL AND OCCASIONAL STG/DAMAGING GUSTS POSSIBLE.
..CENTRAL/SRN HIGH PLAINS...
ISOLATED TO WIDELY SCATTERED TSTMS MAY DEVELOP DURING MID-LATE
AFTERNOON AND PERSIST INTO EARLY EVENING BEFORE DIABATIC SFC COOLING
REMOVES BOUNDARY LAYER BUOYANCY. MOST INTENSE TSTMS MAY PRODUCE
STG/DAMAGING GUSTS AND ISOLATED LARGE HAIL. DEEP-LAYER VERTICAL
SHEAR GENERALLY SHOULD BE WEAK ACROSS THIS CORRIDOR...ALTHOUGH SOME
LOW LEVEL VEERING/STRENGTHENING OF FLOW WITH HEIGHT WILL PRODUCE
ENLARGED 0-3 KM AGL HODOGRAPHS. SOMEWHAT ENHANCED ANVIL LEVEL WINDS
ACROSS WRN/NRN KS AND SRN NEB ALSO MAY ENHANCE VENTING ALOFT AND
OVERALL STORM ORGANIZATION. COVERAGE WILL BE LIMITED BY CAPPING AND
BY LACK OF MORE ROBUST CONVERGENCE INVOF LEE TROUGH/DRYLINE.
..SWRN CONUS...
TSTMS MAY DEVELOP GRADUALLY THROUGH AFTERNOON HOURS AS STG SFC
HEATING WEAKENS CAP...AND AS AMBIENT WIND FIELDS ALOFT INTENSIFY
AHEAD OF AMPLIFYING PACIFIC COAST TROUGH. FCST SOUNDINGS SUGGEST
FAVORABLE SFC DEW POINTS OF 40S AND 50S F ACROSS MUCH OF CENTRAL/SRN
AZ...WITH MOIST ADVECTION OFFSETTING BOUNDARY LAYER MIXING ENOUGH TO
MAINTAIN FAVORABLE MOISTURE DURING DIURNAL HEATING CYCLE. NEARLY
UNIDIRECTIONAL DEEP-LAYER WINDS ARE EXPECTED EXCEPT FOR
LOCALIZED/OROGRAPHIC EFFECTS...AND PRIMARY CONCERN WITH ANY
SUSTAINED TSTMS THAT DO DEVELOP WILL BE STG/DAMAGING GUSTS.
POTENTIAL LIMITING FACTORS INCLUDE LACK OF MORE ROBUST BOUNDARY
LAYER LIFT...GIVEN ABSENCE OF SUBSTANTIAL BAROCLINICITY OVER
REGION...AND MRGL MIDLEVEL LAPSE RATES LIKELY TO CONTINUE S OF
MID/UPPER JET MAX...LIMITING MLCAPES TO AOB 500 J/KG IN MANY AREAS.
HOWEVER...WEAK LARGE SCALE ASCENT AHEAD OF EJECTING SRN STREAM
PERTURBATION MAY BE ENOUGH TO PRESERVE CAPE OVER THIS AREA AND
SUPPORT CONVECTIVE POTENTIAL.
.EDWARDS/CROSBIE.. 10/04/2007
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