SWODY1
SPC AC 051955
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0255 PM CDT SAT SEP 05 2009
VALID 052000Z - 061200Z
...NO SVR TSTM AREAS FORECAST...
...NRN INTERMOUNTAIN REGION...
CURRENT FORECAST APPEARS ON TRACK.
STRONG SHORT WAVE TROUGH CURRENTLY MOVING ONTO THE WA/ORE COASTS IS
FORECAST TO WEAKEN SLIGHTLY WHILE PROGRESSING NEWD THROUGH THE NRN
ROCKIES. NONETHELESS...THIS SYSTEM WILL BE PRECEEDED BY A ZONE OF
ENHANCED FORCING FOR ASCENT WHICH SHOULD SERVE TO FOCUS INCREASINGLY
DEEP CONVECTION THIS AFTERNOON INTO TONIGHT ALONG ASSOCIATED SURFACE
FRONT. AIR MASS IS RELATIVELY DRY WITH PW VALUES AOB .75 INCH.
HOWEVER...STEEPENING LAPSE RATES AND STRENGTHENING VERTICAL SHEAR
MAY PROMOTE A FEW STRONGER STORMS CAPABLE OF LOCALLY STRONG WIND
GUSTS AND PERHAPS SOME HAIL.
...AZ...
THE ONLY CHANGE TO REGION IS THE ADDITION OF A 5% HAIL AREA.
TSTMS HAVE BECOME FAIRLY NUMEROUS TODAY FROM THE HIGHER TERRAIN OF
CNTRL AZ SWD INTO THE LOWER CO VALLEY. MORE RECENT...VIGOROUS TSTM
DEVELOPMENT HAS OCCURRED ALONG THE WRN EDGE OF THICKER CLOUDS OVER
LA PAZ AND YUMA COUNTIES. HERE...AIR MASS HAS BECOME HOT AND IS
QUITE MOIST WITH MLCAPE OF 1500-2500 J/KG. BACKGROUND ASCENT SHOULD
CONTINUE TO BE AIDED BY SRN FRINGE OF MIDLEVEL IMPULSE MOVING EWD
THROUGH THE REGION...AND THIS SUGGESTS THAT TSTM ACTIVITY WILL
PERSIST INTO TONIGHT. WHILE VERTICAL SHEAR WILL REMAIN RELATIVELY
WEAK...WATER LOADING EFFECTS AND MERGING STORM-SCALE OUTFLOWS WILL
PRESENT SOME WIND THREAT. HAIL MAY ACCOMPANY THE STRONGER CORES AS
WELL.
..MEAD.. 09/05/2009
.PREV DISCUSSION... /ISSUED 1129 AM CDT SAT SEP 05 2009/
...SOUTHWEST TO INTERMOUNTAIN WEST...
ABUNDANT MOISTURE AND BACKGROUND ASCENT ASSOCIATED WITH THE PASSAGE
OF SEVERAL SHORT WAVE PERTURBATIONS WILL CONTINUE TO CONTRIBUTE TO
FAIRLY EXTENSIVE CONVECTION FROM LOWER CO RIVER VALLEY NWD/NEWD
ACROSS THE GREAT BASIN/INTERMOUNTAIN REGIONS TODAY. LIMITED
INHIBITION INDICATED IN MORNING SOUNDINGS ALSO SUPPORTS A GRADUAL
INCREASE IN STORM COVERAGE WITH DIURNAL HEATING CYCLE. UNLIKE RECENT
DAYS...MORNING SOUNDINGS SHOW GREATER LOW LEVEL MOISTURE AND THERE
ARE MORE ONGOING STORMS EARLY TODAY. THUS...ANY MICROBURST/WIND
DAMAGE POTENTIAL WILL LIKELY OCCUR WITH MORE PERSISTENT STORM
ACTIVITY MOVING INTO AREAS EXPERIENCING GREATER HEATING THROUGH THIS
AFTERNOON. GIVEN WEAK FLOW REGIME AND EXTENT OF ONGOING CONVECTION
AND CONVECTIVE DEBRIS...SEVERE POTENTIAL FROM WIND/HAIL APPEARS
LIMITED. HOWEVER...SLOW/ERRATIC CELL MOTIONS COULD RESULT IN LOCALLY
EXCESSIVE RAINFALL.
...ID/MT BORDER AREA...
STRONG DYNAMIC FORCING FOR ASCENT/HEIGHT FALLS WILL ACCOMPANY THE
APPROACH OF A PAC NW UPPER TROUGH ACROSS THE INTERIOR NW TODAY.
STEEPENING LAPSE RATES AND SOME MOISTENING ASSOCIATED WITH THE
APPROACH OF THIS SYSTEM COULD BOOST TSTM POTENTIAL ACROSS THE
BITTERROOT MOUNTAINS BY LATE AFTERNOON. DESPITE LACK OF GREATER LOW
LEVEL MOISTURE...IT DOES APPEAR THAT RELATIVELY HIGH-BASED
CONVECTION WILL OCCUR AMIDST INCREASING SHEAR. THIS ACTIVITY WILL BE
FURTHER FOCUSED WITHIN SURFACE PRE-FRONTAL TROUGH AND COULD POSE
SOME THREAT OF ISOLATED DAMAGING WINDS AND PERHAPS SOME HAIL.
...ELSEWHERE...
PERSISTENT WEAK ASCENT ASSOCIATED WITH SMALL-SCALE VORTEX WILL
CONTINUE TO ACT ON MOIST AND DIURNALLY WARMED AIR MASS TO PROVOKE
SHOWERS AND TSTMS FROM AR/MO EWD ACROSS THE MIDDLE MS VALLEY. WEAK
FLOW AND MARGINAL LAPSE RATES SHOULD PRECLUDE SEVERE.
THERE IS A SIGNAL IN SOME GUIDANCE INDICATING AN INCREASE IN OVERALL
STORM COVERAGE AND PERHAPS INTENSITY ACROSS THE MS DELTA REGION
THROUGH THE DAY. FORCING/FOCUS FOR THIS DEVELOPMENT APPEARS
AMBIGUOUS OTHER THAN PERHAPS AN INCREASE IN LOW LEVEL MOISTURE FLUX
INTO THE REGION AND GULF BREEZE DEVELOPMENT. WEAK FLOW BUT MORE THAN
SUFFICIENT MOISTURE AND WEAK CAP COULD LEAD TO AN INCREASING CHANCE
FOR WET MICROBURSTS THIS AFTERNOON. LIMITED FOCUS ATTM PRELUDES
TRYING TO DELINEATE A GREATER PROBABILITY AREA.
A SIMILAR ENVIRONMENT EXISTS ACROSS SRN FL. HERE...
OUTFLOW/DIFFERENTIAL HEATING FROM A PERSISTENT CLUSTER OF STORMS
OVER THE KEYS MAY INTERACT WITH GULF BREEZE BOUNDARIES TO SUPPORT AN
ISOLATED DOWNBURST WIND EVENT OVER THE NEXT SEVERAL HOURS. AGAIN THE
PROBABILITY OF THIS EVENT BASED ON DURATION/COVERAGE APPEARS QUITE
LOW BUT IS ALSO NON-ZERO.
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