SWODY1
SPC AC 041950
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0250 PM CDT FRI SEP 04 2009
VALID 042000Z - 051200Z
...NO SVR TSTM AREAS FORECAST...
...SRN GREAT BASIN SWD THROUGH THE MOGOLLON RIM...
WIDELY SCATTERED TSTMS ARE BEGINNING TO DEVELOP THIS AFTERNOON
WITHIN ZONE OF INCREASING DEEP ASCENT IN ADVANCE OF WELL-DEFINED
SHORT WAVE TROUGH MOVING THROUGH THE SIERRA NEVADA RANGE. GOES
SOUNDER PW IMAGERY INDICATES THE PRESENCE OF A LOW-LEVEL MOISTURE
AXIS /I.E. PW VALUES RANGING FROM 0.75-1.25 INCHES/ DEVELOPING NWD
IN ADVANCE OF THIS SYSTEM. WHEN COUPLED WITH STEEP LOW TO MIDLEVEL
LAPSE RATES...ENVIRONMENT HAS BECOME WEAKLY TO MODERATELY UNSTABLE
WITH MLCAPE OF 500-1000 J/KG.
WHILE VERTICAL SHEAR SHOULD REMAIN RELATIVELY WEAK THROUGH THE
REMAINDER OF THE DIURNAL HEATING CYCLE...THE PRESENCE OF THE STEEP
LAPSE RATES AND INCREASED FORCING FOR ASCENT MAY SUPPORT ISOLATED
STRONG TO MARGINALLY SEVERE STORMS CAPABLE OF LOCALLY STRONG WIND
GUSTS.
FOR ADDITIONAL NEAR-TERM GUIDANCE ON THIS REGION...SEE MCD 1994.
...SRN PLAINS INTO OZARK PLATEAU...
MID/HIGH-LEVEL WIND FIELD ATTENDANT TO VORTICITY MAXIMUM OVER ERN
KS/WRN MO HAS DIMINISHED OVER THE PAST 24 HOURS WITH GENERALLY 20-25
KT 6 KM FLOW PRESENT TO THE S OF SYSTEM PER AREA PROFILER AND VWP
DATA. NONETHELESS...BREAKS IN THE CLOUDS HAVE ALLOWED FOR INCREASED
DIABATIC HEATING TO OCCUR INVOF WEAK SURFACE FRONT FROM NRN OK/SRN
KS ESEWD INTO AR/SERN MO. HERE...BOUNDARY LAYER REMAINS RELATIVELY
MOIST WITH DEWPOINTS IN THE 60S...CONTRIBUTING TO MLCAPE OF
1000-2000 J/KG.
INFLUENCE OF MIDLEVEL VORTICITY MAXIMUM ON DESTABILIZING AIR MASS
SHOULD SUPPORT AN INCREASE IN STORM COVERAGE THIS AFTERNOON...
PARTICULARLY ACROSS PARTS OF ERN OK...SRN MO AND NRN AR. LOCALLY
STRONG STORMS ARE POSSIBLE...BUT THE WEAK VERTICAL SHEAR SHOULD TEND
TO LIMIT A MORE ORGANIZED SEVERE THREAT.
FARTHER S...SCATTERED TSTMS HAVE DEVELOPED ALONG A DIFFERENTIAL
HEATING BOUNDARY FROM THE PERMIAN BASIN INTO THE BIG COUNTRY WHERE
AIR MASS HAS BECOME MODERATELY UNSTABLE WITH MLCAPE OF 1000-1500
J/KG. HERE TOO...STORMS SHOULD CONTINUE TO INCREASE IN COVERAGE
THROUGH THE AFTERNOON...PERHAPS DEVELOPING ESEWD TOWARD THE HILL
COUNTRY. GUSTY WINDS AND SOME HAIL MAY ACCOMPANY THE STRONGER
STORMS...THOUGH ANY SEVERE WEATHER THREAT SHOULD REMAIN QUITE SMALL.
..MEAD/COOK.. 09/04/2009
.PREV DISCUSSION... /ISSUED 1116 AM CDT FRI SEP 04 2009/
...SRN PLAINS...
WEAK DEEP-LAYER CYCLONIC VORTEX/SHORT WAVE TROUGH ROTATING AROUND
LARGER SCALE TROUGH CENTERED ACROSS THE MIDWEST HAS PRODUCED 20-30M
500MB HEIGHT FALLS ACROSS THE PLAINS LAST 12H. THIS FEATURE HAS
SEVERAL WEAKLY CONFLUENT SFC TROUGHS/OUTFLOW BOUNDARIES ASSOCIATED
WITH IT FROM KS INTO NRN TX THIS MORNING. LIFT ACCOMPANYING THESE
FEATURES WILL COMBINE WITH POCKETS OF STRONGER DIURNAL
DESTABILIZATION AND RESULT IN SCATTERED TSTM DEVELOPMENT THROUGH
THIS FORECAST PERIOD.
CYCLONIC MID LEVEL FLOW AOB 30KT ACCOMPANYING THE SHORT WAVE
TROUGH...AND POTENTIAL FOR GREATEST SURFACE HEATING ACROSS THE
OZARKS...SUGGEST THAT SOME INCREASE IN MARGINALLY ORGANIZED
MULTICELL STORM CLUSTERS IN THIS AREA THROUGH LATE AFTERNOON.
GENERALLY WEAK SHEAR AND MARGINAL LAPSE RATES SUGGEST THAT THESE
STORMS WILL ONLY A LOW PROBABILITY OF PRODUCING SEVERE HAIL/WIND.
FARTHER S ACROSS WEST TX...DIFFERENTIAL HEATING BOUNDARY WAS
PERSISTING FROM SOUTH PLAINS ESEWD ACROSS THE CAPROCK. IT IS
POSSIBLE THAT ANOTHER BAND OF MORE VIGOROUS CONVECTION COULD DEVELOP
ALONG AND SOUTH OF THIS ZONE GIVEN SUPPORTIVE BACKGROUND ASCENT ON
THE SWRN FLANK OF THE SHORT WAVE TROUGH. MOIST LOW LEVEL ESELY FLOW
TOPPED BY WEAK WLY FLOW ALOFT MAY CONTRIBUTE TO POCKETS OF GREATER
EFFECTIVE SHEAR AND SOME POTENTIAL FOR A FEW BETTER ORGANIZED
STORMS. A COUPLE OF THESE CELLS COULD PRODUCE SEVERE HAIL OR
DAMAGING OUTFLOW GUSTS BUT OVERALL FOCUS/POTENTIAL AND DURATION OF
THIS THREAT DOES NOT APPEAR TO WARRANT HIGHER PROBABILITIES AT THIS
TIME.
...SOUTHWEST/GREAT BASIN...
STORMS WILL AGAIN DEVELOP ACROSS THESE LARGER REGIONS TODAY DRIVEN
PRIMARILY BY HEATING AND TERRAIN. DRY ADIABATIC SUB-CLOUD LAPSE
RATES...AND PERHAPS MORE PERSISTENT ACTIVITY AHEAD OF WEST COAST
SHORT WAVE TROUGH DEVELOPING INLAND TOWARD THE LOWER CO RIVER
VALLEY...MIGHT SUPPORT A FEW ISOLATED DOWNBURST WIND EVENTS.
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