Tuesday, October 28, 2008

DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 280805
SWOD48
SPC AC 280805

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0305 AM CDT TUE OCT 28 2008

VALID 311200Z - 051200Z

...DISCUSSION...

LATEST MEDIUM-RANGE GUIDANCE IS IN GENERAL AGREEMENT IN THE
EVOLUTION OF THE LARGE-SCALE PATTERN THROUGH THE EXTENDED PERIOD.
HOWEVER...DIFFERENCES DO EXIST IN THE DETAILS OF THE
FORECAST...PARTICULARLY AFTER ABOUT D6 /SUN NOV 2ND/.

MIDLEVEL RIDGING CENTERED OVER THE SPINE OF THE ROCKIES AT THE
BEGINNING OF THE PERIOD WILL BREAK DOWN WHILE SHIFTING EWD INTO THE
CNTRL CONUS IN ADVANCE OF AN EVOLVING LARGE-SCALE TROUGH OVER THE
ERN PACIFIC AND WRN STATES. IN THE E...A MIDLEVEL TROUGH AXIS WILL
PERSIST FROM THE NWRN ATLANTIC SWWD INTO THE ERN GULF OF MEXICO INTO
D6. AT THIS JUNCTURE...THE DETERMINISTIC RUNS OF THE ECMWF AND GFS
BEGIN TO DIVERGE ON THE EVOLUTION OF THE WRN U.S. TROUGH. THE GFS
IS MORE AGGRESSIVE IN EJECTING A SHORT WAVE TROUGH EWD INTO THE
CNTRL PLAINS ON D6 WITH THIS SYSTEM AMPLIFYING OVER THE UPPER
MIDWEST ON D7 /MON NOV 3RD/. IN CONTRAST...THE ECMWF MOVES A MORE
SIGNIFICANT SHORT WAVE TROUGH INTO THE CNTRL U.S. ON D7 INTO D8 /TUE
NOV 4TH/.

PERSISTENT LOW-LEVEL RIDGING FROM THE EAST COAST INTO THE GULF OF
MEXICO WILL TEND TO INHIBIT THE RETURN OF A FULLY MODIFIED AIR MASS
TO THE PLAINS AND MS VALLEY IN ADVANCE OF UPPER TROUGH AND
ASSOCIATED COLD FRONT. NONETHELESS...GIVEN THE INCREASED
LARGE-SCALE FORCING AND VERTICAL SHEAR WITH THE ARRIVAL OF THIS
SYSTEM...SOME SEVERE WEATHER IS POSSIBLE TOWARD THE END OF THE
PERIOD. HOWEVER...DUE TO THE UNCERTAINTIES IN QUALITY OF MOISTURE
RETURN AND THE TIMING OF THE TROUGH...NO SEVERE WEATHER AREA WILL BE
HIGHLIGHTED.

..MEAD.. 10/28/2008

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