SWODY3
SPC AC 210730
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 AM CDT FRI MAY 21 2010
VALID 231200Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE SUN AFTN AND SUN NIGHT
FROM PARTS OF THE CENTRAL PLAINS AND MID MISSOURI VALLEY INTO THE
UPPER MISSISSIPPI VALLEY...
...SYNOPSIS...
VARIABILITY EXISTS AMONG THE MODELS CONCERNING THE LARGE-SCALE
PATTERN DEVELOPMENTS FOR THIS FORECAST PERIOD.
BUT...GENERALLY...GUIDANCE CONTINUES TO SUGGEST THAT UPPER RIDGING
WILL CONTINUE TO BUILD ALONG AN AXIS FROM PARTS OF THE LOWER AND
MIDDLE MISSISSIPPI VALLEY INTO AREAS NORTHWEST OF THE LOWER GREAT
LAKES REGION. AS THIS OCCURS...THE INITIAL SIGNIFICANT IMPULSE
LIFTING OUT OF LARGER SCALE TROUGHING OVER THE WEST IS PROGGED TO
CONTINUE NORTH OF THE CENTRAL INTERNATIONAL BORDER AREA...TOWARD
HUDSON BAY. AT THE SAME TIME...THE UPSTREAM IMPULSE IS PROGGED TO
CEASE DIGGING ...GRADUALLY TURNING EAST OF CALIFORNIA INTO THE GREAT
BASIN. SUBSTANTIVE MID-LEVEL HEIGHT FALLS ASSOCIATED WITH THE
LATTER FEATURE APPEAR LIKELY TO REMAIN WEST OF THE PLAINS INTO EARLY
SUNDAY...WHILE MID-LEVEL HEIGHTS GENERALLY RISE ACROSS THE UPPER
MISSISSIPPI VALLEY. MEANWHILE...A DIGGING IMPULSE WITHIN AN
EVOLVING BROAD CIRCULATION ACROSS THE MID/SOUTH ATLANTIC SEABOARD
AND ADJACENT WESTERN ATLANTIC MAY CONTRIBUTE TO AT LEAST WEAK
MID-LEVEL HEIGHT FALLS ACROSS THE SOUTHEAST.
...PLAINS INTO UPPER MISSISSIPPI VALLEY...
DETAILS OF ANTICIPATED CONVECTIVE EVOLUTION...AND THE EXTENT OF THE
SEVERE POTENTIAL...ARE STILL VERY UNCLEAR FOR SUNDAY. MID 60S TO
AROUND 70F SURFACE DEW POINTS ADVECTING NORTHWARD THROUGH THE
CENTRAL U.S. APPEAR LIKELY TO CONTRIBUTE TO MODERATE TO STRONG
INSTABILITY BY THE PEAK AFTERNOON HEATING HOURS. STRONGEST
INSTABILITY...CHARACTERIZED BY CAPE ON THE ORDER OF 3000
J/KG...APPEARS LIKELY TO BECOME FOCUSED IN A CORRIDOR ALONG AND
SOUTH OF A STALLING...WEAKENING AND THEN RETREATING SURFACE FRONT
ASSOCIATED WITH THE UPPER IMPULSE LIFTING INTO CANADA. DURING THE
LATE AFTERNOON AND EARLY EVENING...THE REMNANT FRONT IS EXPECTED TO
EXTEND FROM PARTS OF WESTERN WISCONSIN/SOUTHEAST MINNESOTA THROUGH
NORTHWEST IOWA/EASTERN AND SOUTHERN NEBRASKA AND NORTHERN
KANSAS...WITH A DRY LINE EXTENDING SOUTHWARD THROUGH THE HIGH
PLAINS...BEFORE RETREATING WESTWARD DURING THE EVENING HOURS.
ALTHOUGH WARM MID-LEVEL TEMPERATURES AND SUBSIDENCE MAY BE
INHIBITIVE...IT APPEARS POSSIBLE THAT LOW-LEVEL FORCING NEAR THE
AFOREMENTIONED SURFACE FEATURES MAY BE SUFFICIENT TO INITIATE
BOUNDARY LAYER BASED STORM DEVELOPMENT PRIOR TO NIGHTFALL. IF THIS
OCCURS...FLOW FIELDS ON THE PERIPHERY OF UPPER RIDGING ARE EXPECTED
TO REMAIN FAVORABLY STRONG AND SHEARED TO SUPPORT SEVERE
STORMS...INCLUDING SUPERCELLS CAPABLE OF LARGE HAIL/DAMAGING WIND
GUSTS...AND PERHAPS A FEW TORNADOES.
ANY BOUNDARY LAYER BASED STORM DEVELOPMENT IS EXPECTED TO SUBSIDE BY
MID TO LATE EVENING WITH THE ONSET OF SURFACE COOLING...AND
INCREASING INHIBITION. BUT...ADDITIONAL STORMS ARE POSSIBLE SUNDAY
NIGHT...BASED WITHIN A STRENGTHENING ELEVATED WARM ADVECTION REGIME
DEVELOPING NORTHWARD THROUGH THE NORTH CENTRAL PLAINS...PERHAPS
ACCOMPANIED BY A CONTINUING RISK FOR LARGE HAIL.
..KERR.. 05/21/2010
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