SWODY2
SPC AC 260553
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1253 AM CDT FRI SEP 26 2008
VALID 271200Z - 281200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS INDICATE THAT THE STRONGER POLAR WESTERLIES WILL REMAIN
MOSTLY NORTH OF THE CANADIAN/U.S. BORDER THROUGH THIS FORECAST
PERIOD. WITHIN THIS REGIME...A STRONG SHORT WAVE TROUGH...NOW OVER
THE NORTHEAST PACIFIC...IS PROGGED TO ADVANCE INLAND ACROSS THE
CANADIAN ROCKIES...THROUGH MUCH OF SASKATCHEWAN BY 12Z SUNDAY. AS
THIS OCCURS...A SIGNIFICANT DOWNSTREAM IMPULSE APPEARS LIKELY TO
CONTINUE TO TRACK EASTWARD NEAR THE CENTRAL CANADIAN/U.S. BORDER
AREA...APPROACHING THE UPPER GREAT LAKES REGION BY 12Z
SATURDAY...BEFORE CONTINUING EASTWARD ACROSS PARTS OF SOUTHERN
ONTARIO AND QUEBEC BY 12Z SUNDAY. IN RESPONSE TO THESE
DEVELOPMENTS...A CLOSED LOW IS EXPECTED TO BEGIN LIFTING NORTH
NORTHEASTWARD OUT OF THE SOUTH ATLANTIC COAST STATES...WHILE KYLE
ACCELERATES NORTHWARD TO ITS EAST...WEST THROUGH NORTH NORTHWEST OF
BERMUDA. WHILE UNCERTAINTY IS STILL FAIRLY LARGE WITH RESPECT TO
THE TRACK OF THE TROPICAL CYCLONE...IT CURRENTLY APPEARS MOST LIKELY
TO PASS EAST OF CAPE COD SOMETIME EARLY TO MID DAY SUNDAY.
SEVERAL AREAS OF SCATTERED THUNDERSTORM ACTIVITY APPEAR POSSIBLE
SATURDAY/SATURDAY NIGHT IN ASSOCIATION WITH THE DEVELOPING
LARGE-SCALE PATTERN. HOWEVER...THE RISK FOR SEVERE STORMS APPEARS
GENERALLY NEGLIGIBLE DUE TO WEAKNESSES IN FLOW/DEEP LAYER
SHEAR...MOISTURE/INSTABILITY...FORCING FOR UPWARD VERTICAL
MOTION...OR SOME COMBINATION THEREOF. AN EXCEPTION COULD DEVELOP
ACROSS PARTS OF THE UPPER MISSISSIPPI VALLEY...WHERE MODELS ARE
SUGGESTIVE THAT STRONGEST DESTABILIZATION WILL OCCUR ASSOCIATED WITH
AN ELEVATED MIXED LAYER ADVECTING EAST OF THE CENTRAL ROCKIES/NORTH
CENTRAL HIGH PLAINS REGION...ON THE SOUTHERN FRINGE OF THE
WESTERLIES.
...UPPER MISSISSIPPI VALLEY...
BENEATH FAIRLY STEEP MID-LEVEL LAPSE RATES...SUFFICIENT MOISTENING
AND HEATING IS EXPECTED TO OCCUR AHEAD OF A WEAK SURFACE COLD FRONT
TO SUPPORT MIXED LAYER CAPE OF 1000-2000 J/KG ACROSS PARTS OF
SOUTHERN/EASTERN IOWA INTO CENTRAL WISCONSIN BY SATURDAY AFTERNOON.
THE FRONT IS EXPECTED IN ASSOCIATION WITH THE SHORT WAVE IMPULSE
PROGRESSING INTO/THROUGH THE UPPER GREAT LAKES. ALTHOUGH IT APPEARS
THAT STRONGER MID-LEVEL FORCING FOR UPWARD VERTICAL MOTION MAY SHIFT
EAST OF THE REGION...WEAKNESS IN INHIBITION BENEATH AN ASSOCIATED
MID-LEVEL THERMAL TROUGH... COUPLED WITH BROADLY DIFLUENT UPPER
FLOW...SHOULD BE SUFFICIENT FOR AT LEAST SCATTERED THUNDERSTORM
ACTIVITY. DEEP LAYER SHEAR IS EXPECTED TO BE RATHER MODEST...BUT
THERMODYNAMIC PROFILES COULD BECOME SUPPORTIVE OF MARGINALLY SEVERE
HAIL AND LOCALIZED DOWNBURSTS BEFORE ACTIVITY WEAKENS SATURDAY
EVENING.
..KERR.. 09/26/2008
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