Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS48 KWNS 310856
SWOD48
SPC AC 310854

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0354 AM CDT MON AUG 31 2015

VALID 031200Z - 081200Z

...DISCUSSION...
THE MEDIUM RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH NORTHWEST
FLOW OVER THE NWRN STATES AND AN UPPER-LEVEL RIDGE OVER THE UPPER
MIDWEST AND WRN GREAT LAKES. THE MODELS BUILD THE UPPER-LEVEL RIDGE
NEWD INTO SERN CANADA ON THURSDAY/DAY 4 AND SHOW A MOIST AIRMASS IN
PLACE FROM THE MS VALLEY EWD TO THE ERN SEABOARD WHERE ISOLATED
THUNDERSTORMS COULD OCCUR. THE GFS AND ECMWF SOLUTIONS MOVE A COLD
FRONT SLOWLY ACROSS THE NRN PLAINS ON FRIDAY/DAY 5 AND SATURDAY/DAY
6...ALONG WHICH THUNDERSTORM DEVELOPMENT WILL BE POSSIBLE ALONG THE
FRONT MAINLY IN THE DAKOTAS AND MN. THE MODELS SUGGEST THAT WIND
FIELDS WILL BE STRONG ENOUGH TO SUPPORT A SEVERE THREAT AND AN
ISOLATED POTENTIAL FOR HAIL AND STRONG WIND GUSTS COULD DEVELOP IN
THE NRN PLAINS EACH AFTERNOON. PREDICTABILITY STILL REMAINS LOW ON
FRIDAY AND SATURDAY DUE TO UNCERTAINTIES CONCERNING THE EXACT
LOCATION OF THE FRONT...AMOUNT OF INSTABILITY AND STORM COVERAGE. ON
SUNDAY/DAY 7...THE UPPER-LEVEL PATTERNS OF THE ECMWF AND GFS MODELS
DIVERGE. HOWEVER...BOTH MODELS CONTINUE TO SHOW THE FRONT IN THE
UPPER MS VALLEY WITH THE ECMWF THE SLOWER OF THE TWO SOLUTIONS.
THUNDERSTORMS WOULD AGAIN BE POSSIBLE ALONG THE FRONT SUNDAY AND A
SEVERE THREAT CAN NOT BE RULED OUT. PREDICTABILITY REMAINS LOW ON
MONDAY/DAY 8 WITH THE TWO SOLUTIONS SUBSTANTIALLY DIFFERENT.

..BROYLES.. 08/31/2015


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