DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 210859
SWOD48
SPC AC 210858

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0358 AM CDT SUN OCT 21 2012

VALID 241200Z - 291200Z

...DISCUSSION...
IN GOOD GENERAL AGREEMENT...00Z ECMWF/GEFS/UKMET IMPLY THAT THE
LONGWAVE PATTERN THROUGH THE MIDDLE/LATE PART OF THE WEEK WILL
GENERALLY BE CHARACTERIZED BY LONGWAVE TROUGHING OVER THE
WESTERN/NORTH-CENTRAL CONUS. A SUBSTANTIAL LEAD PORTION OF THIS
TROUGH IS EXPECTED TO STEADILY SPREAD NORTHEASTWARD FROM THE CENTRAL
ROCKIES TO THE NORTH-CENTRAL CONUS/CANADA BETWEEN DAYS 4-6
WEDNESDAY-FRIDAY...DRIVING A COLD FRONT EAST-SOUTHEASTWARD ACROSS
THE CENTRAL CONUS.

AS THIS UPPER TROUGH/COLD FRONT ENCOUNTER A RELATIVELY MOIST AIRMASS
FOR AUTUMN...AT LEAST SOME SEVERE TSTMS ARE PROBABLE ON DAYS 4-5
WEDNESDAY/THURSDAY. INITIALLY...ORGANIZED SEVERE TSTMS COULD OCCUR
ACROSS PORTIONS OF THE MIDDLE MO VALLEY/UPPER MIDWEST ON DAY
4/WEDNESDAY. CURRENT INDICATIONS ARE THAT THE SEVERE RISK COULD
SPREAD EASTWARD/POSSIBLY BECOME A BIT MORE WIDESPREAD INTO DAY
5/THURSDAY ACROSS THE MIDDLE/UPPER MS VALLEY...PERHAPS AS A
FAST-MOVING/LOW-TOPPED SQUALL LINE. WHILE AT LEAST SOME SEVERE TSTMS
ARE PROBABLE ON THESE DAYS PROVIDED SUFFICIENT
INSTABILITY...LINGERING GUIDANCE VARIABILITY REGARDING UPPER TROUGH
AMPLITUDE/TIMING AND THE EXACT DEGREE OF DESTABILIZATION PRECLUDE A
DELINEATION OF ANY SPECIFIC SEVERE RISK AREAS.

..GUYER.. 10/21/2012

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