SWODY2
SPC AC 210538
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1238 AM CDT SAT MAR 21 2009
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODEL GUIDANCE REMAINS IN GENERALLY GOOD AGREEMENT IN THE EWD
PROGRESSION OF A POWERFUL MIDLEVEL LOW AND ACCOMPANYING 90+ KT JET
STREAK THROUGH THE GREAT BASIN INTO THE CNTRL/SRN HIGH PLAINS BY
MONDAY MORNING. A WEAKER...LEAD IMPULSE NOW EVIDENT IN WATER VAPOR
IMAGERY NEAR 29N/123W WILL PRECEDE THE PRIMARY UPPER
SYSTEM...LIFTING NEWD THROUGH THE GREAT PLAINS TOWARD THE MS VALLEY.
AT THE SURFACE...LOW PRESSURE INITIALLY OVER CNTRL/ERN MT WILL
GRADUALLY REFORM SWD ALONG HIGH PLAINS LEE TROUGH...EVENTUALLY
ANCHORING OVER ERN CO WHERE IT WILL UNDERGO NOTABLE DEEPENING SUNDAY
NIGHT. PACIFIC FRONT ATTENDANT TO THE UPPER SYSTEM WILL PROGRESS
EWD THROUGH THE GREAT BASIN AND ROCKIES BEFORE REACHING THE HIGH
PLAINS BY THE END OF THE FORECAST PERIOD. MEANWHILE...A LEE TROUGH
SITUATED OVER THE HIGH PLAINS WILL GRADUALLY TRANSITION TO MORE OF A
DRYLINE OVER THE CNTRL/SRN HIGH PLAINS PRIOR TO BEING OVERTAKEN BY
PACIFIC COLD FRONT MONDAY MORNING. ELSEWHERE...A WARM FRONT WILL
REMAIN POSITIONED FROM THE CNTRL/ERN DAKOTAS INTO THE MID MS VALLEY.
...GREAT PLAINS...
DESPITE THE MAINTENANCE OF A 30-40+ KT SLY LLJ THROUGH THE
PERIOD...BOUNDARY LAYER MOISTURE WILL REMAIN QUITE MARGINAL ACROSS
SYSTEM WARM SECTOR WITH DEWPOINTS LINGERING IN THE 40S TO LOWER 50S.
MOREOVER...MODEL GUIDANCE SUGGESTS THAT CONSIDERABLE MID AND
HIGH-LEVEL CLOUDINESS WILL ACCOMPANY THE LEAD SHORT WAVE
TROUGH...EFFECTIVELY LIMITING AFTERNOON HEATING. THE NET RESULT IS
THAT AIR MASS IS FORECAST TO BECOME ONLY MARGINALLY UNSTABLE WITH
MLCAPE AOB 500-1000 J/KG.
FORCING ASSOCIATED WITH LEAD SHORT WAVE TROUGH IS EXPECTED TO
CONTRIBUTE TO DIURNAL TSTM DEVELOPMENT BY AFTERNOON FROM PORTIONS OF
CNTRL/ERN SD SWD THROUGH CNTRL NEB/WRN KS INTO THE TX PNHDL...NEAR
OR TO THE E OF SURFACE LEE TROUGH/DRYLINE. VERTICAL SHEAR /BOTH IN
THE LOW LEVELS AND THROUGH A DEEP LAYER/ WILL STEADILY STRENGTHEN
THROUGH THE DAY WITH KINEMATIC ENVIRONMENT BECOMING INCREASINGLY
FAVORABLE FOR ORGANIZED/ROTATING UPDRAFTS. WHILE SOME HAIL AND
GUSTY WINDS WILL ACCOMPANY THE STRONGER STORMS...THE MARGINAL
INSTABILITY WILL LIMIT A MORE SUBSTANTIAL SEVERE WEATHER THREAT.
CLUSTERS OF ELEVATED TSTMS /SOME CAPABLE OF HAIL/ WILL PERSIST
SUNDAY NIGHT FROM THE MID MO INTO UPPER MS VALLEYS ALONG LLJ WHERE
ASCENT/DESTABILIZATION WILL BE FOCUSED. ADDITIONAL STORMS /SOME
STRONG/ WILL BE POSSIBLE MONDAY MORNING ALONG PACIFIC FRONT OVER THE
CNTRL HIGH PLAINS AS MORE INTENSE DYNAMIC FORCING ASSOCIATED WITH
PRIMARY UPPER SYSTEM BEGINS TO OVERSPREAD WRN EDGE OF INSTABILITY
AXIS.
CURRENTLY...IT APPEARS THAT THE MARGINAL INSTABILITY WILL LIMIT A
MORE ORGANIZED SEVERE WEATHER THREAT THROUGH THE DAY TWO PERIOD.
THEREFORE...ONLY LOW SEVERE PROBABILITIES HAVE BEEN INCLUDED. AN
UPGRADE TO SLIGHT RISK MAY BE REQUIRED IN SUBSEQUENT OUTLOOKS ONCE
FINER-SCALE DETAILS IN THE FORECAST BECOME MORE CLEAR.
..MEAD.. 03/21/2009
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