SWODY1
SPC AC 020059
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 PM CDT WED SEP 01 2010
VALID 020100Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL-NRN PLAINS...
...SYNOPSIS...
UPPER AIR PATTERN ACROSS CONUS REMAINS DOMINATED BY RIDGING JUST
OFFSHORE W COAST...AND TROUGHING FROM CENTRAL HIGH PLAINS NWD OVER
SK. STG SHORTWAVE TROUGH NOW INDICATED OVER NRN MT...IS FCST TO
AMPLIFY FURTHER AND MOVE ESEWD ACROSS NRN PLAINS. THIS TROUGH
SHOULD EXTEND FROM N-CENTRAL ND TO ERN WY BY 12Z.
MEANWHILE...WEAKER/PRECURSORY TROUGH IS MOVING NEWD ACROSS SRN
MB...ERN ND...AND CENTRAL SD. TAIL END OF THIS TROUGH --
CORRESPONDING TO VEERING FLOW AT NRN CO PROFILER BETWEEN 18-19Z AND
PLUME OF UPPER MOISTURE EVIDENT IN MOISTURE CHANNEL IMAGERY -- HAS
REACHED ERN CO/NEB BORDER REGION. LEADING TROUGH -- CONSIDERABLY
WEAKER THAN MT PERTURBATION -- IS FCST TO CONTINUE LOSING DEFINITION
AS IT EJECTS AWAY FROM SYNOPTIC TROUGH POSITION THROUGH REST OF
PERIOD.
AT SFC...OCCLUDED CYCLONE OVER CENTRAL ND IS FCST TO WEAKEN AS
TRIPLE-POINT LOW NOW OVER N-CENTRAL SD BECOMES PRIMARY SYNOPTIC
CYCLONE. AS THIS LOW MOVES NEWD TO NWRN MN...ATTACHED WARM FRONT
SHOULD MOVE NEWD FROM CURRENT POSITION OVER SERN SD AND NRN
IA...REACHING W-CENTRAL/SERN MN BY 12Z. COLD FRONT EXTENDS FROM
TRIPLE POINT SWD ACROSS SWRN SD AND E-CENTRAL WY...AND SHOULD REACH
SWRN MN...SERN SD...AND SWRN NEB BY END OF PERIOD. THIS FRONT WILL
OVERTAKE RETREATING DRYLINE NOW ANALYZED FROM NEB SANDHILLS SSWWD
ACROSS EXTREME ERN CO AND WRN PANHANDLE OF TX.
...PORTIONS NORTHERN-CENTRAL PLAINS...
PRE COLD-FRONTAL BAND OF CONVECTION -- INCLUDING A FEW STG-SVR TSTMS
-- HAS DEVELOPED FROM SERN ND SSWWD ACROSS E-CENTRAL SD...WITH
POTENTIAL FOR BACKBUILDING INTO RELATIVELY MOIST LLJ THIS EVENING.
REF WW 640 AND RELATED MESOSCALE DISCUSSIONS FOR NEAR-TERM THREAT.
ADDITIONAL DEVELOPMENT MAY OCCUR INVOF COLD FRONT AS WELL...AS
FORCED ASCENT ALONG THAT BOUNDARY OVERCOMES CAPPING EVIDENT IN 00Z
ABR RAOB. FAVORABLE LOW-LEVEL SHEAR WAS EVIDENT IN ABR RAOB AND
CONTINUES IN MODIFIED RUC SOUNDINGS FROM ERN SD TO E-CENTRAL/NERN
NEB...WITH 40-50 KT EFFECTIVE SHEAR MAGNITUDES. LOW-LEVEL SHEAR
WILL REMAIN ENHANCED INVOF WARM FRONTAL ZONE WHERE NEAR-SFC WINDS
ARE BACKED...YIELDING CORRIDOR OF EFFECTIVE SRH ABOVE 250 J/KG IN
SUPPORT OF SUPERCELL POTENTIAL WITH ANY RELATIVELY
DISCRETE/SUSTAINED ACTIVITY.
...CENTRAL-SRN PLAINS...
SWD EXTENT OF ADDITIONAL SFC-BASED CONVECTION AND OF SVR POTENTIAL
ALONG/AHEAD OF COLD FRONT IS UNCERTAIN GIVEN PRESENCE OF GENERALLY
WEAKER LOW-LEVEL WINDS/SHEAR...AND ALSO...STRONGER MLCINH WITH BOTH
EWD AND SWD EXTENT. SCATTERED TSTMS THAT HAVE DEVELOPED OVER ERN
NEB MAY PERSIST IN SOMEWHAT DISORGANIZED MULTICELLULAR FORM...GIVEN
WEAKER EFFECTIVE SHEAR OVER THIS REGION...BUT VERY RICH LOW-LEVEL
MOISTURE AND 2000-2500 J/KG MLCAPE BASED ON 00Z OAX RAOB. AIR MASS
BECOMES CONSIDERABLY MORE STABLE SWD INTO NERN KS...PER TOP
SOUNDING. POTENTIAL FOR OCCASIONAL HAIL AND ISOLATED DAMAGING GUSTS
EXISTS WITH THIS ACTIVITY...BUT WITH MRGL ORGANIZATION AND SEVERITY.
MEANWHILE MORE ISOLATED ACTIVITY OVER CENTRAL KS COULD PERSIST FOR A
FEW MORE HOURS ALONG WRN RIM OF STG CAPPING...IN NARROW CORRIDOR OF
FAVORABLE MOISTURE/BUOYANCY AND ENHANCED LOW-LEVEL CONVERGENCE NE OF
MESOLOW. ADVECTION OF RELATIVELY STABLE BOUNDARY LAYER AIR FROM
FARTHER E AND SE...AS WELL AS DIABATIC SFC COOLING...IS EXPECTED TO
STRENGTHEN MLCINH AND REDUCE MLCAPE WITH TIME. SVR POTENTIAL OVER
SRN PLAINS IS EXPECTED TO CONTINUE DIMINISHING WITH TIME AS BOUNDARY
LAYER AIR MASS STABILIZES FROM COMBINATION OF EXPANDING OUTFLOW
POOLS AND DIABATIC COOLING NEAR SFC. ISOLATED STG-SVR GUSTS WILL
REMAIN POSSIBLE FOR ANOTHER COUPLE HOURS.
..EDWARDS.. 09/02/2010
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