Severe Storm Outlook Narrative (AC)
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000
ACUS48 KWNS 170859
SWOD48
SPC AC 170858

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0358 AM CDT WED SEP 17 2014

VALID 201200Z - 251200Z

...DISCUSSION...
THE ECMWF AND GFS MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH A SUBTLE
UPPER-LEVEL TROUGH OVER THE UPPER MS AND MID MO VALLEYS AND MOVE
THIS FEATURE EWD INTO THE MID TO UPPER MS VALLEY ON SATURDAY/DAY 4.
A COLD FRONT IS FORECAST TO MOVE SEWD INTO KS...NEB..IA AND WI
DURING THE DAY...ALONG WHICH THUNDERSTORM DEVELOPMENT WITH SOME
POSSIBLY SEVERE...WILL BE POSSIBLE LATE SATURDAY AFTERNOON. THE
MODELS AMPLIFY THE UPPER-LEVEL TROUGH AND MOVE IT EWD ACROSS THE
GREAT LAKES REGION ON SUNDAY/DAY 5. ALTHOUGH THE ECMWF SOLUTION IS
SLOWER WITH THE SYSTEM...BOTH ECMWF AND GFS HAVE A COLD FRONT SUNDAY
AFTERNOON LOCATED FROM THE UPPER OH VALLEY SWWD INTO THE MID MS
VALLEY. THUNDERSTORMS MAY DEVELOP ALONG THE BOUNDARY AND A FEW COULD
BECOME SEVERE LATE SUNDAY AFTERNOON. BOTH MODELS MOVE THE
UPPER-LEVEL TROUGH EWD INTO THE OH AND TN VALLEYS ON MONDAY/DAY 6
WITH THE ECMWF AGAIN THE SLOWER SOLUTION. A COLD FRONT REACHES THE
CAROLINAS AND GULF COAST STATES MONDAY AFTERNOON...ALONG WHICH
THUNDERSTORM DEVELOPMENT WILL AGAIN BE POSSIBLE LATE MONDAY
AFTERNOON. MODEL SOLUTIONS DIVERGE SHARPLY ON TUESDAY/DAY 7.

AT THIS POINT...THE GREATEST SEVERE THREAT DURING THE DAY 4 TO 8
PERIOD IS FORECAST ON SATURDAY AFTERNOON IN THE UPPER MS VALLEY AND
WRN GREAT LAKES REGION. UNCERTAINTY CONCERNING INSTABILITY AND
TIMING REMAINS TOO HIGH TO WARRANT ADDING A SEVERE THREAT AREA.

..BROYLES.. 09/17/2014



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