Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 280849
SWOD48
SPC AC 280847

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0347 AM CDT SUN AUG 28 2016

VALID 311200Z - 051200Z

...DISCUSSION...
THE MEDIUM RANGE MODELS INCLUDING THE ECMWF AND GFS BEGIN THE DAY 4
TO 8 PERIOD WITH AN UPPER-LEVEL TROUGH OVER THE NERN STATES AND AN
UPPER-LEVEL RIDGE IN THE CNTRL AND NRN HIGH PLAINS. BOTH MODELS MOVE
THE UPPER-LEVEL RIDGE SLOWLY EWD ACROSS THE GREAT PLAINS ON
WEDNESDAY/DAY 4 AND THURSDAY/DAY 5 AS SFC HIGH PRESSURE DOMINATES
MUCH OF THE ERN THIRD OF THE NATION. THE GREATEST CHANCE FOR A
MARGINAL SEVERE THREAT WOULD BE LATE THURSDAY AFTERNOON IN THE CNTRL
AND NRN HIGH PLAINS WHERE AN AXIS OF INSTABILITY AND SOUTHWEST
MID-LEVEL FLOW IS FORECAST IN THE WAKE OF THE UPPER-LEVEL RIDGE. ON
FRIDAY/DAY 6...THE ECMWF AND GFS SOLUTIONS MOVE THE INSTABILITY AXIS
EWD ACROSS THE GREAT PLAINS SUGGESTING AN ISOLATED SEVERE THREAT
COULD DEVELOP THERE FRIDAY AFTERNOON. FOR SATURDAY/DAY 7...BOTH THE
ECMWF AND GFS SOLUTIONS HAVE AN UPPER-LEVEL TROUGH IN THE WRN U.S.
AND SOUTHWEST MID-LEVEL FLOW OVER THE NCNTRL STATES. HOWEVER...THE
INSTABILITY PATTERN FOR EACH MODEL IS QUITE DIFFERENT WITH THE GFS
DEVELOPING INSTABILITY MUCH FURTHER EAST. AN ENSEMBLE OF THE TWO
SOLUTIONS WOULD PUT THE GREATEST POTENTIAL FOR A SEVERE THREAT
SATURDAY AFTERNOON IN ERN PARTS OF THE NRN PLAINS EXTENDING EWD INTO
THE MS VALLEY. THIS SAME GENERAL AREA COULD AGAIN HAVE A MARGINAL
THREAT ON SUNDAY/DAY 8 IF THE MODELS ARE SOMEWHAT CLOSE TO CORRECT.
OVERALL...THE ECMWF AND GFS SOLUTIONS HAVE CONSIDERABLE VARIANCE
CONCERNING THE FINER-SCALE DETAILS DURING THE LATTER HALF OF THE DAY
4 TO 8 PERIOD SUGGESTING PREDICTABILITY IS LOW IN THAT TIMEFRAME.

..BROYLES.. 08/28/2016


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