SWODY1
SPC AC 060554
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1154 PM CST THU MAR 05 2009
VALID 061200Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS FRI NIGHT INTO EARLY SAT ACROSS
PARTS OF THE E CNTRL PLAINS AND MIDDLE MS VALLEY....
...SYNOPSIS...
MODELS INDICATE THAT A VIGOROUS SHORT WAVE TROUGH...NOW PROGRESSING
THROUGH THE CREST OF A SHARP EASTERN PACIFIC UPPER RIDGE...WILL DIG
TO LEE OF THE RIDGE AXIS...ACROSS THE NORTHEAST PACIFIC...INTO THE
CANADIAN ROCKIES BY 12Z SATURDAY. AS THIS OCCURS...A SPLIT IN THE
DOWNSTREAM UPPER FLOW REGIME IS PROGGED TO BECOME MORE
PRONOUNCED...WITH A SIGNIFICANT NORTHERN STREAM SHORT WAVE TROUGH
TURNING EASTWARD ACROSS THE CENTRAL CANADIAN PROVINCES...WHILE AN
INCREASINGLY DETACHED SOUTHERN STREAM IMPULSE DIGS ACROSS THE
NORTHERN INTERMOUNTAIN REGION INTO THE GREAT BASIN. SUBTROPICAL
RIDGING IS FORECAST TO REMAIN STRONG ACROSS THE SOUTH CENTRAL AND
SOUTHEASTERN STATES...AND RIDGING MAY BUILD AHEAD OF THE SLOWER
SOUTHERN STREAM IMPULSE...ACROSS THE CENTRAL PLAINS AND MIDDLE
MISSISSIPPI VALLEY. MODELS SUGGEST THAT THIS WILL OCCUR AS THE BASE
OF THE NORTHERN STREAM SHORT WAVE TROUGH PROGRESSES ALONG THE
CENTRAL INTERNATIONAL BORDER AREA...TOWARD THE UPPER GREAT
LAKES...CONTRIBUTING TO AN INTENSIFYING HIGH LEVEL JET IN AN ARC
FROM THE MID MISSOURI VALLEY THROUGH THE GREAT LAKES AND NORTHEAST.
...EAST CENTRAL PLAINS INTO THE OHIO VALLEY...
IN RESPONSE TO THE EVOLVING UPPER FLOW PATTERN...A SIGNIFICANT
LOWER/MID TROPOSPHERIC BAROCLINIC ZONE IS EXPECTED TO BECOME
QUASI-STATIONARY ACROSS PARTS OF NORTHEAST KANSAS/SOUTHEAST NEBRASKA
THROUGH THE IOWA/MISSOURI BORDER AREA INTO THE OHIO VALLEY. AN
ASSOCIATED SURFACE FRONT MAY ADVANCE SOUTH OF THIS POSITION AND
LINGER THROUGH MUCH OF THE DAY...AS A RETURN FLOW OF MOISTURE
CONTINUES OFF THE GULF OF MEXICO INTO THE CENTRAL PLAINS/OZARK
PLATEAU. CHARACTERIZED BY SURFACE DEW POINTS IN THE MID/UPPER
50S...THIS MOISTURE RETURN DOES NOT APPEAR PARTICULARLY
SUBSTANTIAL...ESPECIALLY GIVEN THE WARMTH OF THE LOWER/MID
TROPOSPHERIC AIR MASS ADVECTING INTO THE REGION FROM THE PLATEAU
REGION. AND...THIS CAPPING IS EXPECTED TO SUPPRESS CONVECTIVE
DEVELOPMENT THROUGH THE DAY...AND PERHAPS WELL INTO THE EVENING
HOURS.
HOWEVER...STRENGTHENING LOWER/MID-LEVEL FRONTOGENETIC FORCING IS
PROGGED ALONG THE MAIN BAROCLINIC BAND LATE THIS EVENING AND
OVERNIGHT. THIS PROBABLY WILL BECOME SUFFICIENT TO SUPPORT
INCREASING CONVECTIVE DEVELOPMENT AFTER 07/06Z. STORMS MAY INITIATE
FIRST ACROSS PARTS OF NORTHEAST KANSAS/SOUTHEAST NEBRASKA ...ON THE
NOSE OF A NOCTURNALLY STRENGTHENING LOW-LEVEL JET ASSOCIATED WITH AN
EVOLVING CENTRAL PLAINS CYCLONE...BEFORE SPREADING/DEVELOPING
EASTWARD ALONG THE FRONTAL ZONE THROUGH THE REMAINDER OF THE PERIOD.
ONE OR MORE CLUSTERS OF STORMS MAY EVENTUALLY FORM...AIDED BY
DIVERGENT UPPER FLOW IN THE RIGHT ENTRANCE REGION OF THE
STRENGTHENING HIGH LEVEL JET STREAK.
FORECAST SOUNDINGS INDICATE THAT ACTIVITY WILL BE BASED ABOVE A
RESIDUAL COOL/STABLE NEAR SURFACE LAYER. BUT...STEEP MID-LEVEL
LAPSE RATES MAY CONTRIBUTE TO CAPE OF 500-1000 J/KG...AND A
FAVORABLE ENVIRONMENT FOR THE PRODUCTION OF LARGE HAIL. THIS WILL
BE ENHANCED BY STRONG SHEAR WITHIN THE ELEVATED INFLOW LAYER...AND
THROUGH THE CONVECTIVE LAYER...SUPPORTIVE OF SIGNIFICANT UPDRAFT
ROTATION.
..KERR/JEWELL.. 03/06/2009
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