SWODY3
SPC AC 310727
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0227 AM CDT MON AUG 31 2009
VALID 021200Z - 031200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
AS A STRONG ZONAL MID/UPPER JET STREAK CONTINUES TO NOSE ACROSS THE
MID LATITUDE PACIFIC...TOWARD THE PACIFIC NORTHWEST COAST... MODELS
INDICATE THAT THE DOWNSTREAM CUT-OFF LOW WILL FINALLY LIFT INLAND
ACROSS COASTAL AREAS...INTO BRITISH COLUMBIA AND WESTERN WASHINGTON
STATE BY LATE WEDNESDAY NIGHT. AS THIS OCCURS...A TROUGH FURTHER
DOWNSTREAM MAY GRADUALLY AMPLIFY OVER THE EASTERN CANADIAN
PROVINCES...BUT THE MAIN POLAR JET SHOULD REMAIN NORTH OF THE
CANADIAN/U.S. BORDER THROUGH THIS PERIOD. WITHIN THE WEAKER FLOW
OVER THE U.S...MID/UPPER RIDGING LIKELY WILL PERSIST ACROSS THE
INTERMOUNTAIN WEST AND ROCKIES...WHILE A CYCLONIC REGIME LINGERS IN
THE EAST. AS A RESULT HIGH MOISTURE CONTENT AIR...AND HIGHEST
THUNDERSTORM PROBABILITIES...ARE EXPECTED TO REMAIN CONFINED TO THE
FLORIDA PENINSULA. HOWEVER...ENOUGH MOISTURE WILL EXIST FOR
SCATTERED THUNDERSTORM ACTIVITY IN STRONGER HEATING ACROSS THE
INTERMOUNTAIN WEST/ROCKIES AND HIGH PLAINS...AND IN A FAVORABLE WARM
ADVECTION REGIME ACROSS THE LOWER PLAINS.
...PLAINS...
MODELS INDICATE THAT A MODEST STRENGTHENING OF NORTHWESTERLY
MID-LEVEL FLOW /30+ KT AT AROUND 500 MB/ WILL OCCUR WEDNESDAY ACROSS
MUCH OF THE CENTRAL PLAINS...ON THE SOUTHERN/WESTERN PERIPHERY OF A
WEAKENING CLOSED LOW ADVANCING SOUTHEASTWARD INTO THE MID MISSOURI
VALLEY. ABOVE LIGHT SOUTHEASTERLY LOW-LEVEL FLOW TO THE EAST OF A
LEE SURFACE TROUGH/DIFFUSE DRY LINE...THIS WILL CONTRIBUTE TO
SUFFICIENT DEEP LAYER SHEAR FOR SEVERE STORMS...POSSIBLY SUPERCELLS.
MID-LEVEL LAPSE RATES ARE PROGGED TO BE STEEP AND LARGE-SCALE
FORCING ASSOCIATED WITH LOWER/MID TROPOSPHERIC WARM ADVECTION WILL
BE FAVORABLE FOR CONVECTIVE DEVELOPMENT. BUT...SEASONABLY MODEST
LOW-LEVEL MOISTURE COUPLED WITH RATHER WARM LOWER/MID-LEVELS WILL
PROBABLY RESULT IN ONLY WEAK TO MODERATE DESTABILIZATION...WITH
CONSIDERABLE INHIBITION. THUS...MARGINAL SEVERE HAIL/WIND GUSTS MAY
BE THE PRIMARY THREATS FROM THE MORE VIGOROUS BOUNDARY LAYER BASED
STORMS...WHICH MAY REMAIN FAIRLY SPARSE IN COVERAGE AT THEIR PEAK
DURING THE LATE AFTERNOON OR EARLY EVENING.
...SOUTHERN PLATEAU...
IT IS UNCERTAIN WHETHER WIND PROFILES WILL REMAIN SUPPORTIVE OF
ORGANIZED PROPAGATION OFF THE HIGHER TERRAIN INTO WEDNESDAY.
HOWEVER...MODELS SUGGEST AN INCREASINGLY MOIST ENVIRONMENT COULD
CONTRIBUTE TO MODERATE POTENTIAL INSTABILITY WITH STRONG SURFACE
HEATING. SOME HAIL IS POSSIBLE...BUT FORECAST THERMODYNAMIC
PROFILES APPEAR MORE FAVORABLE FOR LOCALIZED DOWNBURSTS WITH STRONG
SURFACE GUSTS...MAINLY DURING THE LATE AFTERNOON AND EVENING HOURS.
..KERR.. 08/31/2009
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