[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 121956
SWODY1
SPC AC 121954

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0154 PM CST TUE DEC 12 2006

VALID 122000Z - 131200Z

...NO SVR TSTM AREAS FORECAST...

AMPLIFIED TROUGH...WITH SEVERAL EMBEDDED SMALLER SCALE IMPULSES...
IS ALREADY BEGINNING TO LIFT OUT OF THE MISSISSIPPI VALLEY...AS
STRONG HIGH-LEVEL JET NOSES TOWARD THE PACIFIC NORTHWEST.  LACK OF
SIGNIFICANT SURFACE CYCLOGENESIS AND WEAK RETURN FLOW...OFF A SLOWLY
MODIFYING BOUNDARY LAYER OVER THE GULF OF MEXICO... CONTINUES TO
MINIMIZE CONVECTIVE POTENTIAL.  AND...THIS IS GENERALLY EXPECTED TO
REMAIN THE CASE THROUGH THE REMAINDER OF THIS FORECAST PERIOD.

...LOWER MISSISSIPPI VALLEY/CENTRAL GULF COAST...
THE MOST SIGNIFICANT ONGOING CONVECTION...INCLUDING SCATTERED
THUNDERSTORMS...IS SHIFTING EASTWARD THROUGH THE CENTRAL GULF
STATES...IN SOUTHERN PORTION OF ELONGATED ZONE OF LOW-LEVEL WARM
ADVECTION/ISENTROPIC ASCENT AHEAD OF UPPER TROUGH AXIS.  THIS IS
WHERE MOISTURE RETURN HAS BEEN MAXIMIZED ALONG PRE-FRONTAL SOUTHERLY
LOW-LEVEL JET AXIS...CONTRIBUTING TO WEAK CAPE.  MID-LEVEL LAPSE
RATES ARE GENERALLY WEAK...HOWEVER...AND LOW-LEVEL FLOW EAST OF THE
LOWER MISSISSIPPI VALLEY IS BEGINNING TO WEAKEN AS  70-90 KT
MID-LEVEL JET STREAK LIFTS OUT OF THE LOWER MISSISSIPPI VALLEY INTO
THE LOWER OHIO VALLEY.  THUNDERSTORM ACTIVITY IS EXPECTED TO
DIMINISH ACROSS MISSISSIPPI/ALABAMA LATE THIS AFTERNOON AS
LARGE-SCALE ASCENT DECREASES.

...MIDDLE MISSISSIPPI/LOWER OHIO VALLEYS...
AN IMPULSE ASSOCIATED WITH THE JET STREAK IS LIFTING NORTHEAST OF
THE OZARK PLATEAU.  STRONGER FORCING WITH THIS FEATURE IS BEGINNING
TO OVERSPREAD NARROW LOW-LEVEL THERMAL RIDGE ACROSS EASTERN MISSOURI
INTO SOUTHERN/CENTRAL ILLINOIS...WHERE HEATING OF BOUNDARY LAYER
WITH LOWER/MID 50S SURFACE DEW POINTS HAS OCCURRED BENEATH DRY SLOT.
 MIXED LAYER CAPE OF 250-500 J/KG IS WEAK...BUT LAPSE RATES ARE
FAIRLY STEEP...AND CONVECTIVE INSTABILITY PRESENT IN SOUNDINGS WILL
PROBABLY BE SUPPORTIVE OF A FEW STORMS WHICH MAY PRODUCE HAIL/WIND
GUSTS APPROACHING OR BRIEFLY EXCEED SEVERE LIMITS.  A BROKEN LINE OF
STORMS APPEARS POSSIBLE ALONG/AHEAD OF THE COLD FRONT LATE THIS
AFTERNOON AND EARLY EVENING...BEFORE THE FRONT PROGRESSES THROUGH
THE REMAINDER OF THE MORE STRONGLY HEATED BOUNDARY LAYER. 
THEREAFTER...POTENTIAL WILL DIMINISH DEEPER INTO THE LOWER OHIO
VALLEY.

...UPPER MISSISSIPPI VALLEY/GREAT LAKES...
PRE-FRONTAL DESTABILIZATION HAS BEEN EVEN WEAKER NORTHWARD INTO
PARTS OF THE UPPER MISSISSIPPI VALLEY/UPPER GREAT LAKES.  BUT...IT
MAY STILL BE SUFFICIENT FOR SCATTERED THUNDERSTORM ACTIVITY...
PRIMARILY AS MID-LEVEL TROUGH AXIS SHIFTS ACROSS WISCONSIN LATE THIS
AFTERNOON INTO THE EVENING HOURS.  AS FORCING CONTINUES EASTWARD
ACROSS THE GREAT LAKES OVERNIGHT...COOLER LOW-LEVEL ENVIRONMENT WITH
WEAKER LOW-LEVEL LAPSE RATES ARE EXPECTED TO RESULT IN DIMINISHING
CONVECTIVE POTENTIAL.

..KERR.. 12/12/2006