DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 270538
SWODY1
SPC AC 270536

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 AM CDT FRI APR 27 2012

VALID 271200Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL PLAINS TO
MO...

...SYNOPSIS...
PROGRESSIVE UPPER-AIR PATTERN FCST THROUGH PERIOD...FEATURING TWO
PRINCIPAL SHORTWAVE TROUGHS NOW OVER WRN CONUS...
1. HIGH-AMPLITUDE TROUGH NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
FROM NRN NV NWWD ACROSS COASTAL BC. EMBEDDED VORTICITY MAXIMA ARE
EXPECTED TO PHASE TOGETHER IN SUPPORT OF CLOSED 500-MB CYCLONE
DEVELOPMENT DURING AFTERNOON...OVER NRN ROCKIES. CYCLONE CENTER
SHOULD REACH SERN MT/NERN WY/WRN SD BORDER REGION BY END OF PERIOD.
MEANWHILE...
2. COMPACT SHORTWAVE TROUGH -- INITIALLY OVER NRN NM/ERN CO BORDER
-- SHOULD MOVE ENEWD ACROSS CENTRAL HIGH PLAINS...REACHING ERN
PORTIONS KS/NEB BORDER REGION BY 28/00Z. THIS FEATURE WILL
DEAMPLIFY SUBSTANTIALLY FROM ABOUT 27/21Z ONWARD...REACHING NRN/ERN
IA AS WEAK VORTICITY LOBE BY END OF PERIOD.

MEANWHILE...STG MID-UPPER LEVEL SHORTWAVE TROUGH -- NOW MOVING SEWD
ACROSS INTERIOR MID-ATLANTIC REGION -- IS EXPECTED TO PIVOT EWD OVER
NEW ENGLAND EARLY IN PERIOD. ASSOCIATED SFC CYCLOGENESIS WILL
AFFECT CANADIAN MARITIMES. TRAILING COLD FRONT WILL DECELERATE
THROUGH AFTERNOON THEN BECOME QUASISTATIONARY OVER CAROLINAS. WRN
LIMB OF BAROCLINIC ZONE WILL MOVE NWD ACROSS SRN PLAINS AND
AR...LOCATED OVER OZARKS AND ERN KS AND CONNECTING TO SFC LOW OVER
E-CENTRAL KS BY 28/00Z. OCCLUDED FRONT WILL EXTEND NWWD FROM LOW
ACROSS NEB/SD TO SFC CYCLONE OVER ERN MT...PRECEDING NRN-STREAM
PERTURBATION. COLD FRONT TRAILING KS LOW WILL EXTEND WSWWD TO NWRN
OK AND NRN TX PANHANDLE BY 28/00Z...WITH DRYLINE EXTENDING SWD TO
N-CENTRAL/NERN OK THEN SSWWD OVER CENTRAL TX. LOW SHOULD MOVE NEWD
ACROSS NRN MO AND WEAKEN OVERNIGHT...WITH COLD FRONT SWWD ACROSS
CENTRAL OK AND NW TX BY 28/12Z.

...CENTRAL PLAINS TO MO...
--- EARLY ---
SCATTERED TSTMS MAY BE ONGOING AT START OF PERIOD...IN PLUME FROM
NEB PANHANDLE AND NERN CO SSEWD ACROSS PORTIONS WRN KS. THIS WILL
REPRESENT NEWD SHIFT OF STG DEEP-LAYER ASCENT PLUME AND ACCOMPANYING
CONVECTIVE REGIME NOW COVERING MUCH OF ERN CO AND EXTENDING INTO WRN
OK PANHANDLE. SVR THREAT BY START OF PERIOD TIME WILL BE MRGL AT
BEST...GIVEN WEAK NEAR-SFC THETAE EXPECTED OVER SWRN NEB AND WRN KS.
ISOLATED HAIL/GUSTS NEAR SVR LEVELS CANNOT BE RULED OUT. THIS
ACTIVITY WILL MOVE NEWD OVER NEB AND WEAKEN BY MIDDAY.

--- AFTERNOON/EVENING ---
RELATIVELY COMPACT CORRIDOR OF SUPERCELL/TORNADO POTENTIAL MAY
DEVELOP AND SHIFT EWD TODAY ACROSS MAINLY KS. LARGE/DAMAGING HAIL
ALSO IS POSSIBLE. SOME UNCERTAINTIES REMAIN REGARDING
TIMING/DURATION OF FAVORABLE SFC HEATING/DESTABILIZATION OVER
PORTIONS CENTRAL-ERN KS...OTHERWISE NARROW CORRIDOR OF EVEN GREATER
SVR PROBABILITIES MAY BECOME APPARENT.

BY EARLY AFTERNOON...CORRIDOR OF FAVORABLE DESTABILIZATION IS
POSSIBLE BEHIND MORNING ACTIVITY AND AHEAD OF SURGING DRYLINE. MOST
PROBABLE LOCATION ATTM APPEARS TO BE ACROSS PORTIONS WRN/CENTRAL
KS...IN ARC FROM N THROUGH ESE OF NEARBY SFC LOW. MODIFIED
RUC/ETA-KF FCST SOUNDINGS SUGGEST MID-UPPER 60S F SFC
TEMPS...CERTAINLY ATTAINABLE WITH EVEN BRIEF SLOT OF PRE-DRYLINE SFC
INSOLATION...WILL BE SUFFICIENT TO YIELD SFC-BASED EFFECTIVE INFLOW
PARCELS AND MLCAPE 500-1500 J/KG. STG VEERING OF WINDS WITH HEIGHT
AND LOW-LEVEL SPEED SHEAR...COMBINED WITH LOW-LEVEL VORTICITY INVOF
SFC LOW AND NEARBY WARM FRONTAL ZONE...SUPPORT RISK FOR SUPERCELLS
WITH LARGE HAIL AND TORNADOES.

EWD-SHIFTING WARM SECTOR SLOT WILL WIDEN AND BECOME MORE BUOYANT
WITH TIME AND EWD EXTENT ACROSS KS DURING MID-LATE AFTERNOON. ARC
OF SVR TSTMS SHOULD DEVELOP....WHETHER SEPARATELY FROM EARLIER
ACTIVITY FARTHER W OR AS SEWD-BUILDING EXTENSION. ACTIVITY
EVENTUALLY MAY MERGE INTO SVR WIND-PRODUCING AND NEARLY CONTINUOUS
ARC. HOWEVER...FOR MUCH OF AFTERNOON INTO EARLY EVENING...PRESENCE
OF SIGNIFICANT ORTHOGONAL COMPONENT OF FLOW ALOFT SUGGESTS DISCRETE
SUPERCELLS WILL REMAIN OVER ERN KS INTO THAT PART OF SWRN MO ALONG
AND SW OF WARM FRONT. PRECONVECTIVE MLCAPE MAY REACH 2500 J/KG IN
E-CENTRAL/SERN KS...WITH 0-1 KM SRH 200-300 J/KG AND EFFECTIVE SHEAR
MAGNITUDES NEAR 50 KT.

EXTENSION OF THREAT INTO N-CENTRAL/NERN OK IS CONDITIONAL DUE TO
SUBSTANTIALLY STRENGTHENED CAPPING LIKELY OVER OK...ALONG WITH
WEAKER LOW-LEVEL CONVERGENCE. SVR PROBABILITIES THEREFORE DIMINISH
WITH SWD EXTENT OVER OK. SVR POTENTIAL SHOULD DIMINISH WITH EWD
EXTENT OVERNIGHT ACROSS S-CENTRAL MO TO MS RIVER AREA.

...SERN CONUS...
SCATTERED TSTMS ARE EXPECTED TO DEVELOP INVOF SFC FRONTAL
ZONE...FROM ERN SC AT LEAST AS FAR WNWWD AS NERN AL...BECOMING
WIDELY SCATTERED TO ISOLATED FARTHER NW WHERE LOW-LEVEL FRONTAL
FORCING WILL BE WEAK. SFC DEW POINTS 60S F...STG HEATING...AND
FRONTAL LIFT WILL BE SUFFICIENT TO REMOVE MLCINH AMIDST 1000-2000
J/KG MLCAPE. LOW-LEVEL FLOW AND SHEAR WILL BE WEAK...BENEATH
GENERALLY 25-35 KT EFFECTIVE SHEAR MAGNITUDE. PRIMARY MODE SHOULD
BE MULTICELLULAR...WITH SPORADIC STG-SVR DOWNDRAFTS AND HAIL
POSSIBLE. CONVECTIVE COVERAGE AND SVR POTENTIAL SHOULD DIMINISH
MARKEDLY AFTER 00Z...DUE TO STABILIZING EFFECTS OF BOTH SFC DIABATIC
COOLING AND CONVECTIVE OUTFLOWS.

..EDWARDS/GARNER.. 04/27/2012

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