DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 080817
SWODY3
SPC AC 080816

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0216 AM CST SAT DEC 08 2012

VALID 101200Z - 111200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
ANY PHASING OF A PAIR OF SHORT WAVE IMPULSES DIGGING INTO LARGER
SCALE UPPER TROUGHING ENCOMPASSING MUCH OF NORTH AMERICA APPEARS
LIKELY TO BE SHORT-LIVED. THE SPREAD AMONG THE MODELS AND MODEL
ENSEMBLES CONTINUES TO INCREASE DURING THIS PERIOD CONCERNING SHORT
WAVE DEVELOPMENTS. BUT GUIDANCE GENERALLY SUGGESTS THAT THE
LARGE-SCALE TROUGH WILL BROADEN...AS THE NORTHERN IMPULSE LIFTS
NORTHEAST OF THE GREAT LAKES REGION THROUGH EASTERN CANADA. THE
PRIMARY ASSOCIATED SURFACE CYCLONE MAY CONTINUE TO DEEPEN AS IT
MIGRATES FROM THE LOWER GREAT LAKES REGION THROUGH THE CANADIAN
MARITIMES. AND DEEP LAYER WEST SOUTHWESTERLY MEAN FLOW MAY CONTINUE
TO STRENGTHEN ACROSS THE COLD FRONT...APPROACHING THE APPALACHIANS
AND LOWER MISSISSIPPI VALLEY/WESTERN GULF COAST EARLY IN THE
PERIOD...EASTWARD THROUGH THE ATLANTIC SEABOARD. HOWEVER...THE
SURFACE FRONT IS EXPECTED TO OUTPACE COOLING ALOFT...AND SECONDARY
FRONTAL WAVE DEVELOPMENT IS FORECAST TO REMAIN WEAK...AS THE
SOUTHERN SHORT WAVE IMPULSE LIFTS NORTHEAST OF THE SOUTHERN PLAINS
AND BECOMES INCREASINGLY SHEARED AS IT PROGRESSES ACROSS THE OHIO
VALLEY INTO THE NORTHEAST.

POTENTIAL FOR THUNDERSTORM ACTIVITY MAY PERSIST AHEAD OF THE
EASTWARD ADVANCING COLD FRONT ACROSS A LARGE PORTION OF THE EASTERN
U.S. ON MONDAY. HOWEVER..PROBABILITIES APPEAR GENERALLY LOW...AND
MOSTLY NEAR THE MINIMUM 10 PERCENT THRESHOLD FOR A CATEGORICAL
THUNDERSTORM LINE...AS WEAK LAPSE RATES LIMIT CAPE... AND
LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION GENERALLY WEAKENS.

...PARTS OF THE NRN GULF STATES INTO THE CUMBERLAND PLATEAU...
IT DOES NOT APPEAR OUT OF THE QUESTION THAT FORCING ASSOCIATED WITH
THE SOUTHERN IMPULSE COULD CONTRIBUTE TO STRONG ENOUGH LIFT IN A
PRE-FRONTAL CORRIDOR SPREADING ACROSS THE REGION DURING THE LATE
MORNING/AFTERNOON TO SUPPORT CONVECTIVE DEVELOPMENT. AND FORECAST
SOUNDINGS SUGGEST THAT...WHILE WEAK...CAPE MAY EXTEND THROUGH THE
FAVORABLE MIXED PHASE LAYER FOR CHARGE SEPARATION AND LIGHTNING.
EMBEDDED WITHIN A 40-50+ KT WEST SOUTHWESTERLY DEEP LAYER MEAN
FLOW...ACTIVITY COULD BECOME VIGOROUS ENOUGH TO ENHANCE THE DOWNWARD
TRANSFER OF HIGHER MOMENTUM TO THE SURFACE WITH POTENTIALLY DAMAGING
WIND GUSTS.

..KERR.. 12/08/2012

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