SWODY2
SPC AC 290559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT TUE APR 29 2008
VALID 301200Z - 011200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
STG SHORTWAVE TROUGH -- NOW OVER PORTIONS KY/OH/INDIANA -- IS FCST
TO PIVOT CYCLONICALLY AROUND DIGGING UPPER CYCLONE DAY-1...BEFORE
WEAKENING AND LIFTING NWD FROM NEW ENGLAND THIS PERIOD. ASSOCIATED
SFC COLD FRONT -- NOW MOVING OFFSHORE MUCH OF ATLANTIC COAST -- WILL
MOVE THROUGH MOST OF GULF OF MEXICO...CUBA AND BAHAMAS BY BEGINNING
OF PERIOD. LARGE POSTFRONTAL ANTICYCLONE AND AREA OF OFFSHORE FLOW
OVER MUCH OF ERN GULF WILL LEAD TO VERY LIMITED MARINE MODIFICATION
THROUGH THIS PERIOD. RESULT WILL BE IN NARROW/WEAK CORRIDOR OF
PARTIALLY MOISTENED CONTINENTAL AIR RETURNING NWD...AS PART OF
SRN/CENTRAL PLAINS WAA REGIME INDUCED BY NEXT MAJOR SYSTEM ALOFT.
LARGE AND COMPLEX UPPER LEVEL CYCLONE APCHG COASTAL PACIFIC NW AND
BC ATTM SHOULD MOVE ESEWD WITH MEAN CYCLONE CENTER REACHING NWRN MT
BY ABOUT 1/00Z. SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY OFFSHORE ORE -- IS FCST TO MOVE EWD TO VICINITY NWRN WY BY
30/12Z...WITH SFC LOW INVOF WY/SD BORDER...AND OCCLUDED FRONT NWWD
ACROSS ERN MT TO SWRN SASK. WARM FRONTOGENESIS IS FCST BY THAT TIME
FROM BLACK HILLS SEWD ACROSS NERN KS. AS BAND OF LARGE SCALE ASCENT
IMMEDIATELY PRECEDING FIRST SHORTWAVE PIVOTS/EJECTS NEWD ACROSS ERN
MT EARLY IN PERIOD...ISOLATED TSTMS MAY FORM INVOF OCCLUDED
FRONT...BUT LIMITED MOISTURE/INSTABILITY WILL PRECLUDE ORGANIZED SVR
THREAT.
STRONGER LEE-SIDE CYCLONE IS FCST TO DEVELOP INVOF KS/CO BORDER BY
1/00Z...SW OF WARM/COLD FRONTAL OCCLUSION POINT THAT SHOULD BE
LOCATED AROUND S-CENTRAL SD. DEVELOPING DRYLINE IS FCST PARALLEL TO
AND 100-200 NM E OF LEE TROUGHING...FROM SFC LOW SWD ACROSS SRN HIGH
PLAINS. PROGS BEGIN TO DIFFER SUBSTANTIALLY IN POSITION OF SFC LOW
BY END OF PERIOD...RELATED TO INCONSISTENCIES IN PROGGED PHASE SPEED
OF SECOND SHORTWAVE TROUGH MOVING OVER NRN GREAT BASIN TOWARD
CENTRAL ROCKIES. HOWEVER...COLD FRONTAL ZONE BY 1/12Z SHOULD ARC
FROM ERN NEB SWD/SWWD THROUGH LOW TO SERN CO.
...CENTRAL HIGH PLAINS...MOSTLY AFTER DARK...
DIURNAL/DRYLINE DEVELOPMENT S OF SFC LOW STILL APPEARS UNLIKELY
BECAUSE OF STG CAPPING UNDER WELL-DEVELOPED ELEVATED MIXED
LAYER...COMBINED WITH IMMATURITY OF MOISTURE RETURN.
ISOLATED TO WIDELY SCATTERED...HIGH-BASED TSTMS ARE POSSIBLE LATE
AFTERNOON INTO EARLY EVENING INVOF SFC LOW AND ADJACENT PORTIONS
FRONTAL ZONE. THAT AREA WILL BE CHARACTERIZED BY RELATIVELY
MAXIMIZED COMBINATION OF SFC HEATING ON HIGH PLAINS...WEAKEST
CINH...AND LOW LEVEL MASS CONVERGENCE AROUND SFC CYCLONE. ANY SUCH
ACTIVITY WOULD POSE RISK FOR HAIL AND STG-SVR GUSTS.
HOWEVER...THREAT APPEARS TOO CONDITIONAL WITHIN ENVIRONMENT OF MRGL
MOISTURE TO PLACE UNDER CATEGORICAL OUTLOOK ATTM. SREF CONSENSUS
INDICATES DAYTIME SFC DEW POINTS INVOF SFC LOW -- WHERE LOW LEVEL
FORCING WILL BE STRONGEST -- WILL ONLY REACH LOW-MID 50S AT BEST.
THIS DISREGARDS A FEW RSM ENSEMBLE MEMBERS THAT INEXPLICABLY AND
ALMOST SPONTANEOUSLY GENERATE AREA OF 60-65 F DEW POINTS ALONG/AHEAD
OF NEB FRONTAL SEGMENT.
TSTM DEVELOPMENT IS MORE PROBABLE FROM EARLY EVENING ONWARD...INVOF
LOW LEVEL FRONTAL ZONE. EXPECT ENVIRONMENT OF STRONG FRONTOGENETIC
FORCING...FAVORABLE LOW-MIDLEVEL LAPSE RATES ABOVE STABLE SFC
LAYER...MAXIMIZED LOW LEVEL LIFT...WAA JUST ABOVE SFC...AND MRGL BUT
INCREASING MOISTURE. FCST SOUNDINGS INDICATE PARCELS BECOMING MORE
NEARLY SATURATED WITH TIME WHILE ISENTROPICALLY LIFTED TO EVENTUAL
LFC...WITH ELEVATED MUCAPES TO AROUND 500 J/KG AND AROUND 50 KT
EFFECTIVE SHEAR. THEREFORE POTENTIAL EXISTS FOR ISOLATED HAIL.
SOME GUSTS TO NEAR SVR LIMITS ALSO ARE POSSIBLE WHERE MOST INTENSE
DOWNDRAFTS PENETRATE COOL BUT RELATIVELY DRY BOUNDARY LAYER.
..EDWARDS.. 04/29/2008
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