SPC Issues Slight Risk For Most Of Area

 SPC AC 200730        DAY 3 CONVECTIVE OUTLOOK      NWS STORM PREDICTION CENTER NORMAN OK    0230 AM CDT SUN MAR 20 2011        VALID 221200Z - 231200Z        ...THERE IS A SLGT RISK OF SVR TSTMS TUE/TUE NIGHT FROM PARTS OF THE    CNTRL PLAINS THROUGH THE MID MS VALLEY...SOUTHWARD INTO THE SRN    PLAINS...        ...SYNOPSIS...    MODELS INDICATE THAT THE LARGE-SCALE TROUGH...LIFTING THROUGH THE    INTERMOUNTAIN WEST AND ROCKIES BY 12Z TUESDAY...WILL GRADUALLY BE    FORCED EASTWARD INTO A CONFLUENT REGIME TO THE SOUTHEAST OF AN    EVOLVING BLOCKING RIDGE OVER THE CENTRAL CANADIAN PROVINCES...AS    ANOTHER AMPLIFYING SHORT WAVE TROUGH APPROACHES THE CALIFORNIA    COAST.  THE PROCESS IN WHICH THIS OCCURS STILL APPEARS LIKELY TO    SUPPORT INCREASING CONVECTIVE POTENTIAL ACROSS PARTS OF THE CENTRAL    U.S...AS A SIGNIFICANT EMBEDDED IMPULSE EMERGES FROM THE SOUTHERN    ROCKIES AND PIVOTS NORTHEASTWARD INTO AND NORTHEAST OF THE MID/LOWER    MISSOURI VALLEY BY TUESDAY EVENING.  AS LARGER SCALE UPPER TROUGHING    TAKES ON AN INCREASINGLY NEGATIVE TILT...STRONGER MID-LEVEL HEIGHT    FALLS ARE PROGGED TO OVERSPREAD THE WARM SECTOR OF A SUB 1000 MB    SURFACE LOW MIGRATING ACROSS THE MID MISSOURI VALLEY AND UPPER    PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY.  THIS FORCING WILL BE    FOCUSED ALONG AND NORTH OF A STRONG MID/UPPER JET STREAK /AROUND 90    KT AT 500 MB/...WHICH APPEARS LIKELY TO GRADUALLY VEER FROM A    SOUTHWESTERLY TO WESTERLY COMPONENT AS IT DEVELOPS EASTWARD ACROSS    THE SOUTH CENTRAL PLAINS/OZARK PLATEAU AND MIDDLE MISSISSIPPI VALLEY    REGION.        AT LOWER LEVELS...STRONG SOUTHERLY LOW-LEVEL JETS MAY BE    CONCENTRATED IN TWO BROAD CORRIDORS...ONE FROM THE SOUTH CENTRAL    PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY...JUST AHEAD OF THE    SURFACE CYCLONE...ANOTHER ON THE PERIPHERY OF A RETREATING SURFACE    RIDGE ACROSS THE OZARK PLATEAU INTO THE LOWER OHIO VALLEY.  THIS    SURFACE RIDGING...CENTERED OVER THE GULF OF MEXICO AND FLORIDA    PENINSULA...STILL APPEARS LIKELY TO IMPEDE SUBSTANTIVE INLAND    BOUNDARY LAYER MOISTURE RETURN.  AND IT STILL APPEARS THAT THE    OVERALL CONVECTIVE POTENTIAL MAY NOT REACH THE LEVELS THAT IT    OTHERWISE COULD...GIVEN THE STRONG FORCING.     HOWEVER...DESTABILIZATION IN THE WARM SECTOR OF THE LOW...SOUTHWARD    ALONG THE DRY LINE INTO THE SOUTHERN PLAINS... SHOULD BE SUFFICIENT    FOR SEVERE STORMS.        ...PLAINS/MISSISSIPPI VALLEY...    CONVECTIVE DEVELOPMENT MAY BE ONGOING EARLY IN THE PERIOD ALONG AND    NORTH OF A WARM FRONT...EXTENDING EAST SOUTHEAST OF THE    LOW...NORTHEAST OF THE MID MISSOURI VALLEY INTO PORTIONS OF THE    UPPER MISSISSIPPI VALLEY.  HOWEVER...THE PRIMARY STORMS OF CONCERN    DO NOT APPEAR LIKELY TO EVOLVE UNTIL LATE TUESDAY AFTERNOON AND    EVENING...NEAR THE LOW AND WARM FRONT ACROSS EASTERN    NEBRASKA/WESTERN IOWA/NORTHWEST MISSOURI.  INITIALLY ACTIVITY MAY BE    IN THE FORM OF SUPERCELLS...BUT FORCING IS EXPECTED TO SUPPORT    UPSCALE GROWTH INTO A MESOSCALE CONVECTIVE SYSTEM THAT SHOULD TRACK    ALONG AND JUST SOUTH OF THE WARM FRONT THROUGH UPPER PORTIONS OF THE    MIDDLE MISSISSIPPI VALLEY TUESDAY EVENING.  DAMAGING WINDS AND LARGE    HAIL LIKELY WILL BE THE MOST PROMINENT CONCERNS...AND IT DOES NOT    APPEAR OUT OF THE QUESTION THAT THIS COULD CONTINUE INTO THE LOWER    OHIO VALLEY OVERNIGHT.        ADDITIONAL SCATTERED STORM DEVELOPMENT IS EXPECTED SOUTH OF THE    SURFACE LOW...ALONG THE DRY LINE...INTO THE SOUTHERN PLAINS.  IN THE    PRESENCE OF STEEP LAPSE RATES...WEAK TO MODERATE CAPE...AND STRONG    SHEAR...A FEW SUPERCELLS ARE POSSIBLE...PRIMARILY WITH LARGE HAIL    AND LOCALLY DAMAGING WIND GUSTS.