SWOD48
SPC AC 210900
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CDT FRI MAY 21 2010
VALID 241200Z - 291200Z
...PREDICTABILITY TOO LOW TO DELINEATE A SVR RISK AREA...
MEDIUM RANGE MODELS INDICATE THAT A SECOND IN A SERIES OF VIGOROUS
SHORT WAVE IMPULSES...EMERGING FROM LARGER SCALE UPPER TROUGHING
OVER THE WESTERN U.S...MAY CONTRIBUTE TO SUBSTANTIVE MID-LEVEL
HEIGHT FALLS ACROSS PARTS OF THE NORTHERN HIGH PLAINS EARLY NEXT
WEEK. HOWEVER...LIKE THE PRECEDING SYSTEM...THE TENDENCY MAY BE FOR
THE SYSTEM TO LIFT OUT WITH A MORE NORTHERLY THAN EASTERLY
COMPONENT...DUE TO THE CONTINUING PRESENCE OF A BLOCKING UPPER RIDGE
OVER PARTS OF THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES REGION.
DUE TO THIS ORIENTATION...IT IS NOT YET CLEAR THAT INSTABILITY/SHEAR
PARAMETERS WILL BECOME FAVORABLE MAXIMIZED TO SUPPORT A REGIONAL
SEVERE WEATHER THREAT...THOUGH THE SEVERE POTENTIAL MAY NOT BE NON
NEGLIGIBLE. THEREAFTER...GUIDANCE IS SUGGESTIVE THAT UPPER RIDGING
WILL REDEVELOP SOUTHWESTWARD INTO THE CENTRAL AND SOUTHERN PLAINS.
THIS PATTERN COULD BECOME MORE SUPPORTIVE OF EVOLVING MESOSCALE
CONVECTIVE SYSTEMS BY LATE NEXT WEEK AS IMPULSES PROGRESS OUT OF THE
WESTERN TROUGH...AND AROUND THE NORTHERN PERIPHERY OF THE
RIDGE...ACROSS THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY INTO
THE GREAT LAKES REGION. BUT...THE PREDICTABILITY OF THESE FEATURES
AT THIS EXTENDED RANGE BECOMES TOO LOW TO CONFIDENTLY DELINEATE A
SEVERE RISK AREA.
..KERR.. 05/21/2010
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