SWODY1
SPC AC 041221
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0721 AM CDT SAT SEP 04 2010
VALID 041300Z - 051200Z
...NO SVR TSTM AREAS FORECAST...
...NRN INTERMOUNTAIN REGION INTO NRN HIGH PLAINS...
LARGE-SCALE TROUGH CENTERED OVER BRITISH COLUMBIA EARLY THIS MORNING
WILL SHIFT EWD THROUGH THE PERIOD IN RESPONSE TO APPROACH OF NEXT
UPSTREAM SYSTEM THROUGH THE GULF OF AK. AS THIS OCCURS...AN
UPSTREAM VORTICITY MAXIMUM AND ATTENDANT MID TO UPPER-LEVEL STREAKS
ALONG THE BRITISH COLUMBIA COAST WILL PROPAGATE SEWD...CONTRIBUTING
TO A NET SEWD DEVELOPMENT/AMPLIFICATION OF BROADER-SCALE TROUGH
THROUGH THE PACIFIC NW AND NRN INTERMOUNTAIN REGION. AT THE
SURFACE...AN ASSOCIATED COLD FRONT WILL PROGRESS EWD ACROSS THE
REGION...SERVING AS THE FOCUS FOR STRONG TO MARGINALLY SEVERE STORMS
THIS AFTERNOON THROUGH EVENING.
SATELLITE-DERIVED PW IMAGERY SHOWS A SLIGHT INCREASE IN MOISTURE
FROM THE ERN PACIFIC THIS MORNING...THOUGH IN GENERAL...AIR MASS
WILL REMAIN RATHER DRY WITH DEW POINTS IN THE 40S AND PW VALUES LESS
THAN AN INCH. HOWEVER...REGION WILL RESIDE WITHIN A PLUME OF STEEP
MIDLEVEL LAPSE RATES...WHICH WHEN COUPLED WITH DAYTIME
HEATING...SHOULD YIELD AFTERNOON MLCAPE OF 250-500 J/KG. THIS
DESTABILIZATION COMBINED WITH INCREASED HEIGHT FALLS/DYNAMIC FORCING
FOR ASCENT IN ADVANCE OF MIDLEVEL TROUGH SHOULD FOSTER SCATTERED
STORM FORMATION ALONG THE FRONT THIS AFTERNOON OVER WRN AND CNTRL
MT. AMBIENT INFLOW AIR MASS WILL BE CHARACTERIZED BY A DEEPLY-MIXED
PBL WITH 40-50 KT OF WLY DEEP-LAYER SHEAR WHICH WILL BE SUPPORTIVE
OF HIGH-BASED STORMS /INCLUDING POSSIBLE SUPERCELLS/ WITH THE THREAT
FOR ISOLATED STRONG WIND GUSTS AND MARGINALLY SEVERE HAIL. TSTMS
SHOULD TEND TO WEAKEN BY MID TO LATE EVENING AS THE BOUNDARY LAYER
COOLS AND SURFACE-BASED CONVECTIVE INHIBITION RAPIDLY ACCUMULATES.
..MEAD/GRAMS.. 09/04/2010
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