DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 070831
SWODY3
SPC AC 070830

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 AM CST FRI DEC 07 2012

VALID 091200Z - 101200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
THE SPREAD AMONG THE MODELS AND MODEL ENSEMBLES CONTINUES TO
INCREASE CONCERNING SHORT WAVE DEVELOPMENTS WITHIN LARGER SCALE
TROUGHING ENCOMPASSING MUCH OF THE INTERIOR OF NORTH AMERICA DURING
THIS FORECAST PERIOD. HOWEVER...MOST GUIDANCE DOES INDICATE THAT AT
LEAST SOME PHASING OF EMBEDDED IMPULSES WILL LEAD TO SHARPENING OF
THE UPPER TROUGH ALONG A POSITIVELY TILTED AXIS EXTENDING FROM
NORTHWEST ONTARIO THROUGH THE TEXAS BIG BEND/ADJACENT MEXICAN
PLATEAU REGION BY 12Z MONDAY. THIS IS FORECAST TO COINCIDE WITH THE
SOUTHEASTWARD ADVANCEMENT OF A COLD INTRUSION THROUGH MUCH OF THE
REMAINDER OF THE PLAINS/MISSISSIPPI VALLEY...INTO THE WESTERN GULF
COAST REGION...AND SIGNIFICANT SURFACE CYCLOGENESIS...MAINLY ACROSS
PARTS OF THE GREAT LAKES REGION INTO SOUTHERN ONTARIO LATE IN THE
PERIOD. AIDED BY THE NORTHWARD ADVECTION OF PRECIPITABLE WATER ON
THE ORDER OF 1.0 TO 1.25 INCHES ALONG AND JUST AHEAD OF THE
FRONT...LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION AND
DESTABILIZATION PROBABLY WILL SUPPORT CONSIDERABLE THUNDERSTORM
ACTIVITY FROM PORTIONS OF THE SOUTHERN PLAINS INTO THE LOWER OHIO
AND TENNESSEE VALLEYS.

...PARTS OF CNTRL/ERN TEXAS INTO LWR MS VALLEY...
SUBSTANTIVE DIFFERENCES EXIST AMONG THE MODELS CONCERNING SURFACE
CYCLOGENESIS...BUT PRIMARY STRENGTHENING OF THE ASSOCIATED 850 MB
JET APPEARS MOST PROBABLE ACROSS THE OHIO VALLEY INTO THE LOWER
GREAT LAKES REGION SUNDAY NIGHT. HOWEVER...DEEPER LAYER FLOW FIELDS
AND SHEAR WILL LIKELY STILL BE STRONG ALONG THE FRONT AS FAR SOUTH
AS THE RIO GRANDE VALLEY. AND SOME STRENGTHENING OF SOUTHWESTERLY
PRE-FRONTAL 850 FLOW /TO AROUND 30-40 KT/ APPEARS POSSIBLE ACROSS
THE SOUTHERN PLAINS THROUGH THE LOWER MISSISSIPPI VALLEY...AS A
SHORT WAVE IMPULSE WITHIN THE BASE OF THE LARGER SCALE TROUGH BEGINS
TO ACCELERATE EAST OF THE SOUTHERN ROCKIES.

VARIABILITY EXISTS AMONG THE MODELS AND MODEL ENSEMBLES WHEN AND HOW
THIS OCCURS...BUT IT DOES NOT APPEAR OUT OF THE QUESTION THAT
STRENGTHENING OF FORCING FOR UPWARD VERTICAL MOTION DOWNSTREAM
COULD CONTRIBUTE TO INITIATION OF STORMS TO THE WARM SIDE OF THE
FRONT BY SUNDAY EVENING. AT THE PRESENT TIME...THIS SEEMS MOST
PROBABLE ACROSS PARTS OF THE ARKLATEX AND SOUTHERN/EASTERN ARKANSAS.
IN THE PRESENCE OF MOIST LOW-LEVELS WITH MODEST MIXED LAYER CAPE OF
500 TO PERHAPS 1000+ J/KG...IT DOES NOT APPEAR OUT OF THE QUESTION
THAT FORCING AND STRONG GENERALLY UNIDIRECTIONAL SHEAR COULD SUPPORT
THE EVOLUTION OF A SOUTHEASTWARD ADVANCING SQUALL LINE OVERNIGHT.
THIS WILL INCLUDE POTENTIAL FOR SEVERE WIND/HAIL...PERHAPS AN
ISOLATED TORNADO OR TWO...BUT LINGERING UNCERTAINTIES REMAIN TOO
LARGE TO INCLUDE AN OUTLOOK OF SLIGHT RISK PROBABILITIES.

..KERR.. 12/07/2012

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