SWODY3
SPC AC 030705
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0205 AM CDT THU SEP 03 2009
VALID 051200Z - 061200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS INDICATE THAT A LARGE COLD MID/UPPER TROUGH AND EMBEDDED
CLOSED LOW WILL GRADUALLY PROGRESS INLAND ACROSS THE PACIFIC
NORTHWEST COAST INTO BRITISH COLUMBIA AND THE NORTHERN INTERMOUNTAIN
REGION DURING THIS PERIOD. THIS LIKELY WILL BE ACCOMPANIED BY A
SIGNIFICANT COLD FRONT...AND STRENGTHENING FLOW FIELDS IN THE
VICINITY OF A SEASONABLY STRONG CYCLONIC MID/UPPER JET...ON THE
ORDER OF 50-70+ KT AROUND 500 MB. OTHERWISE... SUBTROPICAL RIDGING
MAY CONTINUE TO BUILD NORTHWESTWARD THROUGH THE GULF COAST STATES
AND MUCH OF THE SOUTHEAST...WHILE A WEAK MID-LEVEL CIRCULATION
REMAINS TRAPPED ACROSS THE OZARK PLATEAU/MIDDLE MISSISSIPPI
VALLEY...ON THE SOUTHWESTERN FLANK OF A LINGERING CYCLONIC SHEAR
AXIS WITHIN GENERALLY WEAK FLOW ENCOMPASSING MUCH OF THE INTERIOR
U.S.
GIVEN LITTLE CHANGE TO THE LARGE-SCALE PATTERN THROUGH MUCH OF THE
NATION...WITH THE POSSIBLE EXCEPTION OF PARTS OF WESTERN/CENTRAL
MONTANA...POTENTIAL FOR ORGANIZED STRONG/SEVERE STORM DEVELOPMENT
SEEMS LIKELY TO REMAIN NEARLY NEGLIGIBLE SATURDAY. HOWEVER...THE
DEVELOPMENT OF WEAK TO MODERATE POTENTIAL INSTABILITY WILL PROBABLY
SUPPORT SCATTERED THUNDERSTORMS ONCE AGAIN ACROSS A LARGE PORTION OF
THE INTERMOUNTAIN WEST/ROCKIES...SOUTHERN PLAINS/OZARK PLATEAU INTO
THE LOWER MISSISSIPPI VALLEY...AND THE FLORIDA PENINSULA.
...MONTANA...
LOW MOISTURE VALUES ACROSS AND TO THE LEE OF THE NORTHERN ROCKIES
LIKELY WILL BE PRIMARY LIMITING FACTOR WITH REGARD TO THE RISK FOR
SEVERE STORMS SATURDAY. LAPSE RATES ARE EXPECTED TO BECOME VERY
STEEP...AND OROGRAPHIC FORCING...COUPLED WITH LARGE-SCALE ASCENT
AHEAD OF THE APPROACHING TROUGH...SHOULD AID THUNDERSTORM FORMATION
IN THE PRESENCE OF STRENGTHENING FLOW/SHEAR ACROSS THE MOUNTAINS OF
WESTERN MONTANA BY LATE AFTERNOON. AS THIS ACTIVITY SPREADS TO THE
EAST OF THE HIGHER TERRAIN...A STRENGTHENING LOW-LEVEL WARM
ADVECTION REGIME ASSOCIATED WITH A DEEPENING SURFACE LOW/LEE TROUGH
MAY CONTRIBUTE TO THE CONSOLIDATION OF CONVECTION INTO AN EVOLVING
STORM CLUSTER. IF THIS OCCURS...EVEN IF WEAK CAPE MINIMIZES THE
RISK FOR LARGE HAIL...THE REMNANTS OF A DEEPLY MIXED BOUNDARY LAYER
WITH LARGE TEMPERATURE/DEW POINT SPREADS WILL BE CONDUCIVE TO
DOWNBURSTS WITH POTENTIALLY STRONG OR DAMAGING WIND GUSTS AROUND THE
GREAT FALLS AREA DURING THE EVENING HOURS.
..KERR.. 09/03/2009
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