SWODY2
SPC AC 310506
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1206 AM CDT MON AUG 31 2009
VALID 011200Z - 021200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS CONTINUE TO INDICATE LITTLE CHANGE TO THE LARGE-SCALE PATTERN
ACROSS THE U.S. FROM MONDAY INTO TUESDAY. WITH THE STRONGER
WESTERLIES CONFINED TO THE HIGHER LATITUDES...WELL NORTH OF THE
CANADIAN/U.S. BORDER...WEAK GENERALLY ANTICYCLONIC UPPER FLOW IS
EXPECTED TO PERSIST ACROSS THE WEST...WHILE A CYCLONIC REGIME
LINGERS IN THE EAST. THE CLOSED LOW OVER THE NORTHEAST PACIFIC MAY
BEGIN TO SHIFT EASTWARD TOWARD THE BRITISH COLUMBIA/ PACIFIC
NORTHWEST COAST LATE IN THE PERIOD...AS A STRONG ZONAL JET NOSES
ACROSS THE MID LATITUDE PACIFIC. AND THIS COULD CONTRIBUTE TO SOME
SHARPENING OR AMPLIFICATION OF THE WESTERN RIDGE ALONG AN AXIS
ACROSS THE INTERMOUNTAIN WEST THROUGH THE CANADIAN ROCKIES...AS A
SMALL CLOSED LOW FINALLY PROGRESSES TO THE LEE OF THE NORTHERN
ROCKIES. THE LATTER CIRCULATION APPEARS LIKELY TO GRADUALLY TURN
SOUTHEASTWARD THROUGH THE NORTHERN PLAINS LATE TUESDAY AFTERNOON
INTO TUESDAY NIGHT.
...SOUTHEAST...
THUNDERSTORM PROBABILITIES ARE EXPECTED TO REMAIN HIGHEST ACROSS
PARTS OF NORTHERN FLORIDA AND THE PENINSULA...WHERE THE ENVIRONMENT
WILL LIKELY NOT HAVE BECOME SIGNIFICANTLY IMPACTED BY LOW-LEVEL
COOLING AND DRYING ACCOMPANYING THE EASTERN UPPER TROUGH.
LARGE-SCALE FORCING WITHIN THE BASE OF THE TROUGH...AND AHEAD OF THE
TROUGH AXIS...IS EXPECTED TO SUPPORT STORM DEVELOPMENT...AS THE
BOUNDARY DESTABILIZES WITH DAYTIME HEATING. WHILE CAPE MAY BECOME
SIZABLE...ON THE ORDER OF 2000 J/KG... FORECAST SOUNDINGS SUGGEST
THAT THIS WILL BE SPREAD OUT OVER A DEEP TROPOSPHERIC LAYER. GIVEN
WARM THERMODYNAMIC PROFILES WITH MODEST TO WEAK LOW/MID LEVEL LAPSE
RATES...IN THE PRESENCE OF WEAK SHEAR...FREQUENT CLOUD TO GROUND
LIGHTNING AND LOCALLY HEAVY RAINFALL APPEAR TO BE MORE OF A CONCERN
THAN THE POTENTIAL FOR STRONG WIND GUSTS.
...PARTS OF THE NORTHERN/CENTRAL HIGH PLAINS...
CONVECTIVE DEVELOPMENT WILL PROBABLY ACCOMPANY THE DIGGING UPPER
LOW/TROUGH INTO PARTS OF THE NORTHERN AND CENTRAL PLAINS TUESDAY/
TUESDAY NIGHT. HOWEVER...WITH GULF MOISTURE RETURN REMAINING CUT
OFF...DESTABILIZATION IS EXPECTED TO BE LIMITED EVEN FOR BOUNDARY
LAYER BASED PARCELS NEAR THE LEE SURFACE TROUGH. EVEN SO...THE
PRESENCE OF STEEP LAPSE RATES AND SHEAR...ASSOCIATED WITH A MODEST
NORTHWESTERLY MID-LEVEL JET STREAK DEVELOPING ON THE SOUTHERN
PERIPHERY OF THE LOW...MAY BE SUFFICIENT FOR A FEW WIDELY SCATTERED
STRONG/SEVERE STORMS NEAR THE SURFACE TROUGH DURING THE LATE
AFTERNOON/EVENING HOURS.
...SOUTHERN PLATEAU...
WIND FIELDS ARE EXPECTED TO REMAIN RATHER WEAK...BUT PROFILES TO THE
SOUTH AND WEST OF A HIGH CENTER ARE EXPECTED TO BE FAVORABLE FOR
STORM PROPAGATION OFF THE HIGHER TERRAIN OF SOUTHEAST ARIZONA INTO
THE LOWER DESERTS. CONVECTIVE ACTIVITY IS EXPECTED TO DEVELOP IN
RESPONSE TO DAYTIME HEATING WITHIN A STEADILY MOISTENING AIR MASS
SUPPORTIVE OF WEAK TO MODERATE POTENTIAL INSTABILITY BY TUESDAY
AFTERNOON. THE RISK FOR LARGE HAIL SEEMS LOW...BUT A VERY WARM AND
DEEPLY MIXED BOUNDARY LAYER WITH SIZABLE TEMPERATURE/DEW POINT
SPREADS SHOULD BE FAVORABLE FOR ISOLATED STRONG DOWNBURSTS.
..KERR.. 08/31/2009
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