Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 040514
SWODY2
SPC AC 040513

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1213 AM CDT FRI SEP 04 2015

VALID 051200Z - 061200Z

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE NRN PLAINS AND UPPER
MS VALLEY...

...SUMMARY...
A FEW STRONG TO SEVERE STORMS WILL BE POSSIBLE OVER A PORTION OF THE
NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY SATURDAY AFTERNOON
AND EVENING.

...NRN PLAINS/UPPER MS VALLEY...

UPPER RIDGE IS EXPECTED TO REMAIN ANCHORED OVER THE SRN PLAINS
THROUGH THE DAY2 PERIOD AS HEIGHTS FALL ACROSS THE NWRN PORTIONS OF
THE CONUS.  IN RESPONSE TO NWRN U.S. TROUGH...WEAK SHORT-WAVE TROUGH
WILL EJECT FROM NRN MEXICO...NNEWD ACROSS THE SRN ROCKIES INTO THE
BLACK HILLS REGION BY DAYBREAK SATURDAY...THEN NEAR THE
INTERNATIONAL BORDER OVER NWRN MN BY EARLY EVENING.  THIS FEATURE IS
EXPECTED TO FOCUS LLJ OVER THE ERN PLAINS OF SD/NEBRASKA BY 06/00Z
WITH LOW-LEVEL WARM ADVECTION MAXIMIZED OVER THE UPPER RED RIVER
REGION ALONG A SW-NE ORIENTED SFC BOUNDARY.  LARGE-SCALE ASCENT
SHOULD AID ELEVATED CONVECTION NORTH OF THIS BOUNDARY DURING THE
FIRST HALF OF THE PERIOD AND NEAR-SFC BASED CONVECTION COULD EVOLVE
OVER THE ERN DAKOTAS INTO MN BY MID-LATE AFTERNOON IMMEDIATELY AHEAD
OF SHORT WAVE.  WHILE FORECAST SHEAR IS NOT PARTICULARLY
STRONG...VEERING WIND WITH HEIGHT AND MODEST 500MB FLOW SUGGEST A
FEW WEAK SUPERCELLS MAY ALSO EVOLVE ACROSS THIS REGION.  WIND/HAIL
ARE THE PRIMARY CONCERNS WITH THIS ACTIVITY.

IN THE WAKE OF THE AFOREMENTIONED SHORT WAVE...STRONG MID-LEVEL
SPEED MAX IS EXPECTED TO TRANSLATE ACROSS THE NRN GREAT BASIN INTO
THE UPPER SNAKE RIVER VALLEY BY 06/00Z.  WEAK MID-LEVEL HEIGHT FALLS
SHOULD SPREAD ACROSS THE NRN ROCKIES BY EARLY EVENING AND SHARPEN A
FRONTAL ZONE ALONG THE MT/WY BORDER.  ISOLATED CONVECTION SHOULD
DEVELOP OVER THE HIGHER TERRAIN BY LATE AFTERNOON NEAR THIS BOUNDARY
FROM THE ABSAROKA RANGE INTO THE BIG HORN MOUNTAINS...THEN SPREAD
NEWD WITHIN A FAVORABLY SHEARED ENVIRONMENT FOR SUPERCELLS.
FORECAST SOUNDINGS ACROSS SERN MT ARE STRONGLY SUPPORTIVE OF
ROTATING UPDRAFTS WITH NELY BOUNDARY-LAYER FLOW AND SWLY 500MB FLOW
ON THE ORDER OF 40KT.  HOWEVER...GREATEST LARGE-SCALE FORCING IS
EXPECTED TO INCREASE ACROSS THIS REGION AFTER DARK AND MORE
CONCENTRATED CONVECTION MAY ACTUALLY MATERIALIZE WITHIN A
LESS-BUOYANT REGIME DURING THE LATTER HALF OF THE PERIOD.  EVEN
SO...SEVERE PROBS MAY NEED TO BE INCREASED ACROSS PORTIONS OF THE
NRN HIGH PLAINS TO ACCOUNT FOR THIS STRONG TROUGH EJECTING INTO
MT/WY LATE IN THE PERIOD.

..DARROW.. 09/04/2015




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