SWODY2
SPC AC 200556
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT FRI APR 20 2007
VALID 211200Z - 221200Z
..THERE IS A MDT RISK OF SVR TSTMS SATURDAY AFTERNOON AND EVENING
OVER WRN KS INTO PORTIONS OF THE OK/TX PNHDLS...
..THERE IS A SLGT RISK OF SVR TSTMS FROM WRN TX NWD INTO PORTIONS
OF THE NRN PLAINS...
..SYNOPSIS...
PROGRESSIVE LARGE-SCALE PATTERN WILL EXIST DURING THE DAY TWO PERIOD
WITH THE PRIMARY FEATURE OF INTEREST BEING SHORT WAVE TROUGH WHICH
WILL TRANSLATE EWD FROM THE LOWER CO VALLEY THROUGH THE SRN
ROCKIES...EVENTUALLY EJECTING NEWD AS A NEGATIVELY TILTED TROUGH
INTO THE CNTRL PLAINS BY SUNDAY MORNING.
IN THE LOW-LEVELS...SURFACE LOW INITIALLY OVER WRN NEB WILL DEVELOP
NEWD INTO THE RED RIVER VALLEY OF THE N BY THE END OF THE PERIOD
WHILE SECONDARY CYCLOGENESIS OCCURS SATURDAY OVER NERN CO. COLD
FRONT TRAILING FROM LEAD SURFACE LOW WILL PUSH SEWD FROM THE NRN
HIGH PLAINS THROUGH THE DAKOTAS AND WRN NEB. MEANWHILE...DRYLINE
ATTENDANT TO NERN CO LEE CYCLONE WILL BECOME INCREASINGLY SHARP
THROUGH THE DAY NEAR THE CO-KS BORDER SWD INTO THE WRN OR CNTRL TX
PNHDL AND INTO WRN TX.
..CNTRL/SRN HIGH PLAINS...
POOR LOW-LEVEL TRAJECTORIES ARISING FROM RIDGING OVER THE ERN U.S.
INTO GULF BASIN ARE EXPECTED TO LIMIT THE QUALITY OF BOUNDARY LAYER
MOISTURE WITHIN WARM SECTOR AIR MASS WITH NOTABLE DIFFERENCES
BETWEEN 20/00Z NAM/WRF AND GFS GUIDANCE IN THE EVOLUTION OF THE
MOISTURE/INSTABILITY FIELDS. FORECAST SOUNDINGS ALSO SUGGEST THAT
MID AND HIGH-LEVEL CLOUDINESS MAY TEND TO INCREASE AHEAD OF EJECTING
UPPER TROUGH...WHICH COULD TEMPER DAYTIME HEATING. HOWEVER...IT
DOES APPEAR THAT LOW/MID 50S DEWPOINTS WILL BE SUSTAINABLE WITH
AFTERNOON MIXING...WHICH WHEN COUPLED WITH STEEP MID-LEVEL LAPSE
RATES WILL CONTRIBUTE TO THE DEVELOPMENT OF AN AXIS OF MODERATE
INSTABILITY WITH MLCAPES OF 1000-1500 J/KG.
TSTMS WILL BECOME INCREASINGLY LIKELY BY AFTERNOON FROM PORTIONS OF
WRN/CNTRL NEB SWD THROUGH WRN KS INTO THE TX/OK PNHDLS AND WRN TX AS
INCREASED LARGE-SCALE FORCING FOR ASCENT AHEAD OF UPPER TROUGH AND
DEEPENING DRYLINE CIRCULATION ACT ON DESTABILIZING AIR MASS. SSWLY
50-70 KT MID-LEVEL JET STREAK WILL CONCURRENTLY PROPAGATE EWD ACROSS
WRN EDGE OF INSTABILITY AXIS WITH DEEP LAYER VERTICAL SHEAR BECOMING
INCREASINGLY SUPPORTIVE OF SUPERCELLS. LARGE HAIL /SOME
SIGNIFICANT/ WILL BE THE PRIMARY SEVERE WEATHER THREAT. TORNADOES
WILL ALSO BE POSSIBLE WITH THE MORE INTENSE STORMS GIVEN THE MODEST
LOW-LEVEL SHEAR AND LCL HEIGHTS. THIS SEVERE WEATHER IS EXPECTED TO
BE FAIRLY CONCENTRATED IN A N-S ZONE IMMEDIATELY E OF DRYLINE LATE
SATURDAY AFTERNOON AND EVENING.
SEVERE POTENTIAL SHOULD TEND TO DIMINISH SATURDAY NIGHT AS STORMS
SHIFT E OF INSTABILITY AXIS OVER THE HIGH PLAINS...THOUGH ISOLATED
LARGE HAIL AND/OR LOCALLY DAMAGING WINDS WILL REMAIN POSSIBLE WITH
THE MOST INTENSE CONVECTIVE ELEMENTS.
..NRN PLAINS...
TSTMS /PERHAPS SLIGHTLY ELEVATED/ MAY BE ONGOING SATURDAY MORNING
ALONG LOW-LEVEL FRONTAL ZONE FROM THE RED RIVER VALLEY SWWD INTO WRN
SD...DRIVEN LARGELY BY RATHER STRONG ISENTROPIC ASCENT INVOF OF THIS
BOUNDARY ON NOSE OF LLJ. THESE STORMS MAY PERSIST THROUGH THE DAY
NEAR FRONTAL ZONE DOWNSTREAM FROM DEVELOPING SURFACE LOW WHERE
ISENTROPIC ASCENT AND WAA WILL BE MAINTAINED BY LLJ. OTHER MORE
VIGOROUS SURFACE-BASED STORMS ARE EXPECTED BY AFTERNOON OVER CNTRL
INTO NERN SD ALONG SURFACE LOW TRACK WHERE AIR MASS WILL BECOME
MODERATELY UNSTABLE WITH MLCAPES OF 1000-1500 J/KG.
FORECAST SOUNDINGS SUGGEST THAT VERTICAL SHEAR WILL BE SUPPORTIVE OF
SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND PERHAPS A
COUPLE OF TORNADOES. OTHER STORMS...MORE LINEAR...WILL LIKELY
DEVELOP ALONG TRAILING COLD FRONT WHERE SEVERE HAIL AND LOCALLY
DAMAGING WINDS WILL BE POSSIBLE.
.MEAD.. 04/20/2007
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