DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 280557
SWODY1
SPC AC 280555

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 AM CDT SAT APR 28 2012

VALID 281200Z - 291200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SRN PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS ERN MO TO OH VALLEY
REGION...

...SYNOPSIS...
KEY UPPER-AIR FEATURE FOR THIS FCST WILL BE STG SHORTWAVE TROUGH AND
EMBEDDED CYCLONE NOW OVER MT/WY. 500-MB CYCLONE CENTER SHOULD BE
LOCATED INVOF BLACK HILLS AT 28/12Z...WITH CONSENSUS AMONG VARIOUS
OPERATIONAL/SREF PROGS FOR GEN NWD DRIFT OVER WRN DAKOTAS THROUGH
PERIOD. BROADLY CYCLONIC FLOW WILL COVER MUCH OF ROCKIES AND GREAT
PLAINS STATES AROUND THIS SYSTEM. PRECEDING/LOWER-AMPLITUDE
PERTURBATION -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY AND
VWP/PROFILER DATA OVER NEB/IA BORDER REGION -- WILL WEAKEN FURTHER
AND MOVE THROUGH IA MEAN RIDGE POSITION EARLY IN PERIOD. SEGMENT OF
ASSOCIATED VORTICITY BANNER WILL BREAK EWD ACROSS WI/SRN LM/LOWER MI
REGION DURING AFTERNOON/EVENING.

AT SFC...CYCLONE NOW OVER NERN KS/SERN NEB REGION IS FCST TO MOVE
EWD ACROSS NRN MO EARLY IN PERIOD AND WEAKEN...WITH REMNANT FRONTAL
WAVE STILL POSSIBLE OVER PORTIONS SRN IL OR ERN MO THIS AFTERNOON.
BY 29/00Z...QUASISTATIONARY FRONT SHOULD EXTEND FROM THAT WAVE EWD
ACROSS OH VALLEY TO NERN KY. COLD FRONT NOW SW OF THAT LOW WILL
SETTLE SEWD ACROSS WRN/NRN OK EARLY IN PERIOD...THEN BY
29/00Z...BECOME QUASISTATIONARY FROM S-CENTRAL MO TO SWRN OK AND NW
TX...THEN WWD ACROSS TX SOUTH-PLAINS REGION. DRYLINE SHOULD EXTEND
FROM FRONTAL INTERSECTION OVER NW TX...SSWWD TO NRN COAHUILA/BIG
BEND AREA.

...SRN PLAINS...
SVR POTENTIAL ACROSS THIS REGION APPEARS IN TWO PRIMARY MODES...EACH
WITH SOME CONDITIONALITIES INVOLVED...

1. NEAR-SFC FRONTAL ZONE...CENTRAL OK TO W-CENTRAL TX...LATE
AFTERNOON INTO EVENING. IT NOW APPEARS THAT AT LEAST ISOLATED TO
WIDELY SCATTERED TSTMS WILL FORM ALONG FRONTAL ZONE DURING LATE
AFTERNOON INTO EARLY EVENING...TAKING ADVANTAGE OF LIFT ALONG
BOUNDARY...SFC DEW POINTS UPPER 50S TO MID 60S F...MLCAPE NEAR 3000
J/KG IN SOME AREAS...AND 45-50 KT EFFECTIVE SHEAR. SUPERCELLS WITH
DAMAGING HAIL AND STG-SVR GUSTS ARE POSSIBLE...THOUGH STORM MERGERS
AND OUTFLOW MAY MAKE MODES MESSY LOCALLY.

TORNADO THREAT WILL DEPEND STRONGLY ON STATUS OF CONVECTIVE MODE BY
ABOUT 00Z-01Z...WHEN LOW-LEVEL HODOGRAPHS ARE FCST TO ENLARGE AND
BECOME FAVORABLE. ANY DISCRETE SUPERCELLS STILL PRESENT AT THIS
TIME MAY ENCOUNTER RELATIVELY BACKED FLOW ALONG SFC FRONT AND
STRENGTHENING LLJ WINDS ABOVE THAT RESULT IN ENHANCED EFFECTIVE SRH.
OTHERWISE...BAND OF FRONTAL TSTMS SHOULD AGGREGATE DURING
EVENING...THEN DIMINISH IN INTENSITY BY ABOUT 06Z AS MLCINH BECOMES
PROGRESSIVELY LESS FAVORABLE.

2. ELEVATED HAIL RISK FROM TX PANHANDLE AND PERHAPS EXTREME NERN NM
ACROSS NWRN OK AND SRN KS OVERNIGHT. MODELS DIFFER ON MESOSCALE
DETAILS OF TIMING/LOCATION. HOWEVER...CONSENSUS FAVORS FORMATION OF
STG/ISOLATED SVR TSTMS WITH HAIL POSSIBLE DURING 29/06Z-29/12Z TIME
FRAME BETWEEN TX PANHANDLE/NM BORDER REGION AND NRN OK/SRN KS.
INCREASING MOISTURE...STEEP MIDLEVEL LAPSE RATES...AND ISENTROPIC
ASCENT TO LFC SHOULD SUPPORT THIS RISK...WITH CORRIDOR OF 1000-2000
J/KG ELEVATED MUCAPE. 55-65 KT EFFECTIVE SHEAR IS FCST...LENDING
SOME CONCERN FOR SIGNIFICANT HAIL OR GREATER COVERAGE THAN OUTLOOK
INDICATES OVER SOME PORTION OF THIS AREA. HOWEVER...SPATIAL/TIMING
UNCERTAINTIES PRECLUDE MORE THAN 5% UNCONDITIONAL FCST ATTM.

...ERN MO TO OH VALLEY REGION...
SCATTERED TSTMS ARE EXPECTED TO DEVELOP INVOF SFC FRONT THIS
AFTERNOON...WITH DAMAGING WIND AND OCNL LARGE HAIL POSSIBLE.
PRIMARY MODE SHOULD BE MULTICELLULAR...THOUGH TRANSIENT SUPERCELL
EVOLUTIONS CANNOT BE RULED OUT...GIVEN PRESENCE OF AT LEAST MRGL
DEEP-LAYER SPEED SHEAR. SVR THREAT SHOULD BE STRONGLY TIED TO
COMBINATION OF DIURNAL CAPE MAX ALONG AND S OF FRONT...AS WELL AS
RELATIVELY MAXIMIZED ASCENT ALONG BOUNDARY NEAR AND E OF FRONTAL
WAVE. ANTECEDENT MOIST ADVECTION SHOULD BOOST SFC DEW POINTS INTO
MID-50S/MID-60S F RANGE OVER THIS CORRIDOR...JUXTAPOSED WITH LAPSE
RATES THAT INCREASE GRADUALLY FROM E-W. RESULT SHOULD BE
PRECONVECTIVE MLCAPE IN 1500-2500 J/KG RANGE...AMIDST 35-45 KT
EFFECTIVE SHEAR MAGNITUDE. TSTMS SHOULD DIMINISH MARKEDLY AFTER
DARK...WITH STABILIZATION RESULTING FROM COMBINATION OF SFC DIABATIC
COOLING AND OUTFLOW POOLS.

..EDWARDS/GARNER.. 04/28/2012

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