DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 230844
SWOD48
SPC AC 230844

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0344 AM CDT THU AUG 23 2012

VALID 261200Z - 311200Z

...DISCUSSION...
TWO PRIMARY AREAS OF CONCERN FOR SEVERE POTENTIAL THIS FORECAST.
FIRST...A TORNADO RISK ASSOCIATED WITH TC ISAAC MAY COMMENCE AS
EARLY AS D4 IN FL BASED ON LATEST NHC TRACK AND CONSENSUS OF
GUIDANCE. THIS MAY PERSIST ACROSS PARTS OF THE SOUTHEAST DURING THE
PERIOD. ALTHOUGH GUIDANCE HAS CONVERGED TO SOME EXTENT ON THE
TRACK/TIMING...CONFIDENCE IS MUCH TOO LOW TO WARRANT HIGH-RISK
EQUIVALENT TORNADO PROBABILITIES /AOA 30 PERCENT/ IN THIS TIME
FRAME.

GUIDANCE DIFFERS SUBSTANTIALLY WITH THE EVOLUTION AND TIMING OF THE
NEXT SHORT WAVE TROUGH TO APPROACH THE PACIFIC NW. DIFFERENCES ARE
FAIRLY PRONOUNCED BETWEEN 12Z ECMWF ENSEMBLE MEAN AND 00Z GEFS MEAN
500 MB HEIGHTS BY D7/WED...WITH THE 00Z ECMWF EVEN FASTER WITH THE
EWD EJECTION OF THE SHORT WAVE IMPULSE. THIS MAY INCREASE SEVERE
POTENTIAL IN THE N-CNTRL CONUS...BUT THE LACK OF RUN-TO-RUN
CONTINUITY RENDERS LOW CONFIDENCE IN THIS ASSESSMENT.

..GRAMS.. 08/23/2012

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