SWODY2
SPC AC 270540
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1240 AM CDT SAT SEP 27 2008
VALID 281200Z - 291200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
THE CLOSED LOW TO THE EAST OF THE SOUTHERN APPALACHIANS IS CURRENTLY
CUT-OFF FROM THE STRONGER WESTERLIES. BUT...MODELS CONTINUE TO
SUGGEST THAT THIS FEATURE WILL BEGIN TO ACCELERATE NORTHEASTWARD
TODAY...AS A SHORT WAVE IMPULSE WITHIN THE WESTERLIES PROGRESSES
ACROSS THE UPPER GREAT LAKES REGION... FOLLOWED BY ANOTHER STRONGER
IMPULSE...NOW PROGRESSING INTO/THROUGH THE CANADIAN ROCKIES. AS THE
INCREASINGLY SHEARED LEAD POLAR IMPULSE CONTINUES EAST THROUGH THE
ST. LAWRENCE VALLEY ON SUNDAY...GUIDANCE INDICATES THAT THE SOUTHERN
CIRCULATION WILL MOVE OFF NORTHERN MID ATLANTIC COASTAL AREAS.
SOUTH/ SOUTHWESTERLY FLOW TO THE EAST OF BOTH THESE FEATURES APPEARS
LIKELY TO STEER KYLE EAST OF CAPE COD AND DOWNEAST MAINE BY LATE
SUNDAY NIGHT/EARLY MONDAY.
MEANWHILE...UPSTREAM...AMPLIFICATION WITHIN THE LARGE-SCALE UPPER
PATTERN IS STILL PROGGED FROM THE EASTERN PACIFIC INTO THE WESTERN
U.S...WITH AN UPPER RIDGE BUILDING NORTHWARD FROM THE INTERMOUNTAIN
WEST INTO THE WESTERN CANADIAN PROVINCES...AS A VIGOROUS SHORT WAVE
TROUGH/CLOSED LOW DIGS WELL WEST OF THE PACIFIC COAST. AS THIS
OCCURS...THE AFOREMENTIONED STRONG SHORT WAVE TROUGH PROGRESSING
EAST OF THE CANADIAN ROCKIES IS FORECAST TO BEGIN DIGGING SOUTHWARD
INTO THE UPPER MISSISSIPPI VALLEY.
...PARTS OF THE NORTHERN PLAINS INTO UPPER MS VLY...
THE LARGE-SCALE PATTERN WILL REMAIN UNSUPPORTIVE OF A STRONG
SOUTHERLY RETURN FLOW OF MOISTURE OFF THE GULF OF MEXICO. BUT...
MODEST MOISTURE LEVELS CURRENTLY EXIST ACROSS THE REGION...AHEAD OF
AN INITIAL COLD FRONT WHICH IS EXPECTED TO STALL ACROSS PARTS OF THE
MIDDLE MISSISSIPPI/MID MISSOURI VALLEY BEFORE WEAKENING/ RETURNING
NORTHWARD SUNDAY. THIS MOISTURE...GENERALLY CHARACTERIZED BY 55-60F
SURFACE DEW POINTS...LIKELY WILL RETURN NORTHWARD THROUGH PARTS OF
THE MID MISSOURI/UPPER MISSISSIPPI VALLEY...CONTRIBUTING TO WEAK TO
MODERATE DESTABILIZATION IN THE PRESENCE OF STEEP THERMAL LAPSE
RATES.
WITH ELEVATED MIXED LAYERS CAPPING ANYTHING BEYOND VERY ISOLATED
CONVECTIVE DEVELOPMENT THROUGH MUCH OF THE DAY...TIMING OF STRONGER
FORCING ASSOCIATED WITH THE APPROACHING UPPER TROUGH IS STILL A
CONCERN. THIS MAY NOT BEGIN TO DEVELOP ACROSS OR OVERSPREAD THE
REGION UNTIL SUNDAY EVENING. BUT...IT APPEARS THERMODYNAMIC
PROFILES WILL REMAIN SUPPORTIVE OF VIGOROUS STORM DEVELOPMENT
CAPABLE OF PRODUCING MARGINALLY SEVERE HAIL/LOCALIZED DAMAGING WIND
GUSTS EVEN AFTER THE ONSET OF BOUNDARY LAYER COOLING. AND...A
BROKEN LINE OF STORMS SEEMS POSSIBLE FROM PARTS OF NORTH CENTRAL
NEBRASKA/SOUTHEASTERN SOUTH DAKOTA INTO SOUTHERN MINNESOTA...BEFORE
SPREADING SOUTHEASTWARD SUNDAY NIGHT.
..KERR.. 09/27/2008
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