[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 180540
SWODY1
SPC AC 180539

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT FRI AUG 18 2006

VALID 181200Z - 191200Z

...NO SVR TSTM AREAS FORECAST...

SUBTROPICAL RIDGING WILL PERSIST ACROSS MUCH OF THE CENTRAL AND
SOUTHERN TIER OF THE U.S. THROUGH THIS FORECAST PERIOD. 
HOWEVER...MODELS INDICATE THAT THE OZARK PLATEAU/MID SOUTH HIGH
CENTER WILL GRADUALLY BEGIN TO BREAK DOWN/WEAKEN...IN RESPONSE TO
THE PROGRESSION OF SHORT WAVE TROUGHS IN FASTER FLOW TO THE
NORTH...AND ASSOCIATED INTRUSIONS OF COOLER AIR INTO THE NORTH
CENTRAL STATES.

THE MOST PROMINENT OF THESE SHORT WAVES...EMBEDDED WITHIN THE
STRONGER BELT OF WESTERLIES ACROSS CANADA...IS PROGGED CONTINUE EAST
OF HUDSON BAY/ONTARIO TODAY...WITH ANOTHER SYSTEM CONTINUING INLAND
EAST OF THE CANADIAN ROCKIES.  AS THIS OCCURS...AN INCREASINGLY
SHEARED SHORT WAVE TROUGH IN A WEAKER SOUTHERN BRANCH OF POLAR
WESTERLIES...IS PROGGED TO ADVANCE ACROSS THE NORTHERN PLAINS...AND
INTO THE UPPER GREAT LAKES REGION BY EARLY SATURDAY MORNING.

...CENTRAL STATES...
CONSIDERABLY COMPLICATING MATTERS...CONCERNING SEVERE POTENTIAL
DURING THIS FORECAST PERIOD...IS SERIES OF WEAK IMPULSES EMBEDDED
WITHIN SUBTROPICAL MOIST PLUME ADVECTING AROUND UPPER HIGH CENTER. 
MODELS SUGGEST THAT A CONVECTIVELY GENERATED/ENHANCED SURFACE
BOUNDARY ASSOCIATED WITH THIS STREAM...LIKELY OVER NORTHERN
KANSAS/NORTHERN MISSOURI AT THE OUTSET OF THE PERIOD...WILL ADVANCE
SOUTHWARD INTO/THROUGH THE OZARKS/CENTRAL PLAINS DURING THE DAY. 
THIS MOVEMENT...INTO AREAS WELL SOUTH OF STRONGER FLOW ASSOCIATED
WITH THE WESTERLIES...IS FORECAST TO OCCUR AS A SIGNIFICANT IMPULSE
SHIFTS EAST OF THE MID/LOWER MISSOURI VALLEY TOWARD THE LOWER OHIO
VALLEY.  LOW-LEVEL CONVERGENCE WILL BECOME FOCUSED ALONG THIS
BOUNDARY...WITH STRONGER SURFACE HEATING AND STEEPER LAPSE RATES
BECOMING CONFINED TO AREAS TO THE SOUTH AND WEST...ACROSS MUCH OF
KANSAS/SOUTHERN MISSOURI.

DESPITE WEAK SHEAR AND UNCERTAIN MID/UPPER FORCING...MIXED LAYER
CAPE IN EXCESS OF 2000 J/KG MAY SUPPORT SCATTERED VIGOROUS STORMS AS
INHIBITION WEAKENS IN PEAK AFTERNOON HEATING ALONG/SOUTH OF
BOUNDARY.  LOCALIZED DOWNBURSTS WILL BE POSSIBLE IN STRONGER
CONVECTION...BUT POTENTIAL FOR A SIGNIFICANT CONVECTIVE CLUSTER WITH
BROADER SCALE DAMAGING WIND POTENTIAL SEEMS SMALL.

ELSEWHERE...AHEAD OF UPPER IMPULSE...SCATTERED THUNDERSTORM ACTIVITY
SEEMS LIKELY TO DEVELOP FROM PARTS OF THE MIDDLE MISSISSIPPI INTO
THE LOWER OHIO VALLEY LATE THIS AFTERNOON.  SHEAR WILL BE
LIMITED...AND SURFACE HEATING/DESTABILIZATION NOT AS STRONG AS AREAS
FARTHER WEST...BUT HIGH PRECIPITABLE WATER CONTENT OF AIR WILL BE
FAVORABLE FOR LOCALLY HEAVY DOWNPOURS...PERHAPS LOCALIZED
DOWNBURSTS.

OTHER STRONG/LOCALLY SEVERE STORMS COULD OCCUR NEAR FRONTAL ZONE
ASSOCIATED WITH SOUTHERN BRANCH TROUGH MIGRATING ACROSS THE NORTH
CENTRAL STATES.  THIS SEEMS MOST LIKELY EARLY IN THE DAY ACROSS
PARTS OF SOUTHERN SOUTH DAKOTA/NORTHERN NEBRASKA...BEFORE LOW-LEVEL
CONVERGENCE WEAKENS AS PRE-FRONTAL LOW-LEVEL FLOW VEERS TO A PROGGED
NORTHERLY COMPONENT.

..KERR/BOTHWELL.. 08/18/2006