SWODY2
SPC AC 041639
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1139 AM CDT FRI SEP 04 2009
VALID 051200Z - 061200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
DYNAMIC MIDLEVEL TROUGH OVER THE ERN PACIFIC WILL BEGIN TO MOVE ONTO
THE BRITISH COLUMBIA/PACIFIC NW COASTS THIS PERIOD AS UPPER JET
STREAK ROTATES THROUGH THE BASE OF SYSTEM AND INTO THE NRN ROCKIES.
THIS EVOLUTION WILL SERVE TO AMPLIFY DOWNSTREAM RIDGE IN PLACE OVER
THE NRN PLAINS...WHILE FARTHER E...POSITIVELY-TILTED MIDLEVEL TROUGH
REMAINS QUASI-STATIONARY FROM THE GREAT LAKES INTO LOWER ELEVATIONS
OF THE SRN PLAINS.
AT THE SURFACE...COLD FRONT ATTENDANT TO NWRN U.S. SYSTEM WILL
PROGRESS EWD THROUGH THE NRN ROCKIES AND GREAT BASIN. ELSEWHERE...A
WEAK BAROCLINIC ZONE WILL PERSIST FROM THE SRN PLAINS INTO OZARKS.
...CNTRL/SRN AZ...
TRENDS IN SURFACE OBSERVATIONS AND GOES PW IMAGERY SHOW THAT A SURGE
OF LOW-LEVEL MOISTURE HAS OCCURRED FROM THE GULF OF CA INTO THE
LOWER CO VALLEY...WHICH SHOULD PERSIST INTO SAT. THIS MOISTURE
COUPLED WITH DAYTIME HEATING ARE EXPECTED TO CONTRIBUTE TO A
MODERATELY UNSTABLE AIR MASS...PARTICULARLY OVER THE LOWER
DESERTS...WITH MLCAPE OF 1000-1500 J/KG.
THE COMBINATION OF OROGRAPHIC ASCENT /DUE TO LOW-LEVEL SLY FLOW/ AND
GLANCING INFLUENCE OF MIDLEVEL SHORT WAVE TROUGH TRANSLATING ENEWD
THROUGH NV/UT SHOULD BE SUFFICIENT TO INITIATE SCATTERED DIURNAL
STORMS OVER THE HIGHER TERRAIN OF NRN/CNTRL/SERN AZ. WHILE VERTICAL
SHEAR WILL REMAIN WEAK...STRONGER STORM CLUSTERS WILL BE CAPABLE OF
LOCALLY DAMAGING WINDS AS THEY MOVE OFF THE HIGHER TERRAIN INTO MORE
UNSTABLE AIR MASS.
...WRN MT...
ISOLATED STRONG STORMS WILL BE POSSIBLE AHEAD OF COLD FRONT SAT
AFTERNOON/EVENING AS DEEP ASCENT ASSOCIATED WITH MIDLEVEL TROUGH
OVERSPREADS REGION FROM THE W. AIR MASS WILL REMAIN RELATIVELY
DRY...BUT THE PRESENCE OF STEEP LOW TO MIDLEVEL LAPSE RATES AND
STRENGTHENING WIND FIELDS MAY SUPPORT SOME STORM ORGANIZATION WITH
THE THREAT FOR GUSTY WINDS AND PERHAPS SOME HAIL. SITUATION APPEARS
TOO MARGINAL TO WARRANT INCLUSION OF SEVERE PROBABILITIES ATTM.
...OK/N TX INTO THE OZARK PLATEAU...
SCATTERED DIURNAL STORMS WILL BE POSSIBLE INVOF WEAK SURFACE
BOUNDARY WITHIN MOIST AND MODERATELY UNSTABLE AIR MASS WITH MLCAPE
OF 1000-1500 J/KG. LOCALLY STRONG STORMS ARE POSSIBLE...THOUGH VERY
WEAK VERTICAL SHEAR AND POOR MIDLEVEL LAPSE RATES WILL LIMIT THE
POTENTIAL FOR ANY ORGANIZED SEVERE WEATHER.
..MEAD.. 09/04/2009
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