Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 040556
SWODY1
SPC AC 040554

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT FRI SEP 04 2015

VALID 041200Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF EASTERN NORTH
DAKOTA/NORTHWEST MINNESOTA...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK
OVER PORTIONS OF CENTRAL/EASTERN NORTH DAKOTA...NORTHEAST SOUTH
DAKOTA AND WESTERN/CENTRAL MINNESOTA...

...SUMMARY...
ISOLATED TO WIDELY SCATTERED SEVERE THUNDERSTORMS WILL BE POSSIBLE
FRIDAY AFTERNOON AND EVENING ACROSS PORTIONS OF EASTERN NORTH
DAKOTA...NORTHEAST SOUTH DAKOTA AND WESTERN MINNESOTA. LARGE HAIL
AND DAMAGING WINDS WILL BE THE MAIN THREATS.

...SYNOPSIS...
A SEASONABLY STRONG/SLIGHTLY AMPLIFYING UPPER-LEVEL TROUGH OVER THE
PACIFIC NORTHWEST WILL MOVE LITTLE FRIDAY AS AN UPPER-LEVEL RIDGE
EXTENDS FROM THE SOUTHERN PLAINS INTO THE GREAT LAKES. AN IMPULSE
WITHIN THE SOUTHWESTERLY MID-LEVEL FLOW OVER THE CENTRAL/NORTHERN
HIGH PLAINS FRIDAY MORNING WILL LIFT NORTHEAST ACROSS THE
DAKOTAS/MINNESOTA DURING THE AFTERNOON/EVENING. A FRONTAL BOUNDARY
WILL EXTEND FROM NORTH DAKOTA SOUTHWEST ACROSS NORTHERN WYOMING LATE
FRIDAY AFTERNOON...WITH ANOTHER QUASI-STATIONARY FRONT FROM
SOUTHERN/CENTRAL MINNESOTA EAST INTO THE OHIO VALLEY.

...PORTIONS OF THE DAKOTAS/MINNESOTA...
SURFACE DEW POINTS IN THE UPPER 60S/LOWER 70S WILL BE PRESENT ACROSS
THE UPPER MIDWEST/NORTHERN PLAINS ON FRIDAY. DESPITE MORNING
CLOUDS/SCATTERED STORMS...DIURNAL HEATING AND A PLUME OF STEEP
MID-LEVEL LAPSE RATES WILL LEAD TO AREAS OF MODERATE-STRONG
SURFACE-BASED INSTABILITY BY AFTERNOON ACROSS CENTRAL/EASTERN
PORTIONS OF THE DAKOTAS EASTWARD INTO MINNESOTA. LOW-MID LEVEL WIND
FIELDS WILL INCREASE SOMEWHAT WITH THE APPROACH OF THE UPPER-LEVEL
IMPULSE DURING THE AFTERNOON/EVENING...RESULTING IN SUFFICIENT
DEEP-LAYER SHEAR /35-40 KTS/ ACROSS THE SLIGHT RISK AREA FOR STORM
ORGANIZATION. EXPECT ISOLATED TO WIDELY SCATTERED THUNDERSTORMS TO
DEVELOP BY LATE AFTERNOON ACROSS EASTERN NORTH DAKOTA AND MOVE
NORTHEAST DURING THE EVENING. WITH ADEQUATE DEEP SHEAR FOR UPDRAFT
ROTATION...LARGE HAIL AND DAMAGING GUSTS WILL BE POSSIBLE WITH THE
MORE DISCRETE STORMS. STORMS MAY TEND TO DEVELOP INTO CLUSTERS WITH
TIME POSING A CONTINUED SEVERE RISK MAINLY IN THE FORM OF DAMAGING
WINDS.

...EASTERN MONTANA/NORTHWEST NORTH DAKOTA LATE FRIDAY NIGHT...
SOME SIGNAL EXISTS IN LATEST GUIDANCE REGARDING THE POTENTIAL FOR
STRONG STORMS IN THE 06Z-12Z SAT TIME FRAME OVER PORTIONS OF EASTERN
MONTANA/NORTHWEST NORTH DAKOTA...WHERE DEVELOPING WARM ADVECTION AND
AN APPROACHING IMPULSE WITHIN SOUTHWESTERLY MID-LEVEL FLOW COULD
PROVIDE SUFFICIENT LARGE-SCALE FORCING FOR ASCENT TO AID IN
THUNDERSTORM DEVELOPMENT. CONSIDERED A WESTWARD EXTENSION OF THE
MARGINAL/5 PERCENT SEVERE PROBABILITIES...HOWEVER WITH QUESTIONS ON
TIMING AND MAGNITUDE OF ELEVATED INSTABILITY/THUNDERSTORM
INTENSITY...OPTED TO DEFER TO LATER OUTLOOKS IN THIS AREA.

..BUNTING/COOK.. 09/04/2015




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