Severe Storm Outlook Narrative (AC)
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000
ACUS48 KWNS 050855
SWOD48
SPC AC 050853

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0353 AM CDT SAT SEP 05 2015

VALID 081200Z - 131200Z

...DISCUSSION...
MEDIUM-RANGE DETERMINISTIC AND ENSEMBLE GUIDANCE INDICATE
AMPLIFICATION OF THE UPPER FLOW PATTERN WILL OCCUR OVER THE NORTH-
CENTRAL STATES STARTING ON DAY 6 /THU SEP 10/...AS A DEEPENING
TROUGH MOVES ACROSS THE UPPER MS VALLEY AND GREAT LAKES THROUGH THE
END OF THE PERIOD ON DAY 8 /SAT SEP 12/.  IN ADVANCE OF THE UPPER
TROUGH...A STRONG SURFACE COLD FRONT WILL PROGRESS EWD/SEWD FROM THE
UPPER MS VALLEY AND CENTRAL PLAINS TOWARD THE ATLANTIC AND GULF
COAST REGIONS AND PROVIDE A FOCUS FOR POSSIBLY STRONG THUNDERSTORMS
DURING THE LATTER HALF OF THE DAY 4-8 PERIOD.

THE 00Z ECMWF DETERMINISTIC MODEL DEVELOPS A NOTICEABLY SHARPER
MID-LEVEL TROUGH WITH CONSIDERABLY STRONGER WINDS ON THE SOUTH SIDE
OF THE SYSTEM COMPARED TO THE 00Z GFS/GEFS MEAN AND 12Z ECMWF
ENSEMBLE MEAN SOLUTIONS.  REGARDLESS OF THE STRENGTH OF THE UPPER
SYSTEM...MODEL CONSENSUS INDICATES THE AMPLIFYING UPPER TROUGH WILL
REMAIN WELL NORTH OF THE SURFACE COLD FRONT...WHICH WILL BE LOCATED
WITHIN A WEAKLY SHEARED ENVIRONMENT AND CHARACTERIZED BY MINIMAL
LOW-LEVEL CONVERGENCE.  ALTHOUGH STRONG STORMS MAY OCCUR AS THE
FRONT MOVES INTO A MOIST AND UNSTABLE AIR MASS FROM DAY 6 THROUGH
DAY 8...CONCERNS ABOUT THE MAGNITUDE OF INSTABILITY AND VERTICAL
SHEAR PRECLUDE DELINEATION OF ANY 15% SEVERE AREAS AT THIS TIME.

..WEISS.. 09/05/2015


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