Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 050548
SWODY2
SPC AC 050547

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1247 AM CDT SAT SEP 05 2015

VALID 061200Z - 071200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF MN...

...THERE IS A MRGL RISK OF SVR TSTMS FROM THE MIDDLE MO VALLEY INTO
THE UPPER MS VALLEY...

...SUMMARY...
A FEW SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER PARTS OF
MINNESOTA SUNDAY AFTERNOON AND EVENING.  OTHER STRONG TO ISOLATED
SEVERE THUNDERSTORMS MAY DEVELOP SOUTHWARD INTO WESTERN IOWA AND
EASTERN NEBRASKA.

...SYNOPSIS...
MODEL GUIDANCE INDICATES THE UPPER FLOW PATTERN WILL GRADUALLY
DEAMPLIFY ON SUNDAY AS THE UPPER LOW CURRENTLY OVER THE PACIFIC NW
MOVES NEWD INTO SRN SASKATCHEWAN...AND HEIGHTS FALL FROM THE NRN
ROCKIES/PLAINS TOWARD THE UPPER MS VALLEY.  AT THE SURFACE...A COLD
FRONT OVER THE DAKOTAS AND WRN NEB AT THE START OF THE PERIOD IS
FORECAST TO PROGRESS EWD/SEWD REACHING FROM WRN MN INTO ERN NEB BY
07/00Z AND CONTINUING TO WRN PARTS OF LAKE SUPERIOR AND WI SWWD
ACROSS CENTRAL IA INTO SWRN KS BY 07/12Z.  THE FRONT IS EXPECTED TO
PROVIDE A FOCUS FOR STRONG/SEVERE THUNDERSTORM DEVELOPMENT MAINLY
DURING THE LATE AFTERNOON AND EVENING.

...MN AREA SWD INTO ERN NEB/WRN IA...
PRE-FRONTAL MORNING CONVECTION AND ASSOCIATED CLOUD COVER OVER THE
UPPER MS VALLEY INTO THE UPPER GREAT REGION LAKES IS EXPECTED TO
MOVE EWD AND DIMINISH BY EARLY AFTERNOON...PERMITTING STRONGER
DIABATIC HEATING TO OCCUR IN THE WAKE OF THE EARLY CONVECTION.
AMPLE LOW-LEVEL MOISTURE IS EXPECTED TO PERSIST WITH MAXIMUM SURFACE
DEW POINTS INTO THE LOWER 70S.  WITH THE ERN EDGE OF A PLUME OF
STEEPER MID-LEVEL LAPSE RATES NEAR 7C/KM EXTENDING TO NEAR THE
ADVANCING COLD FRONT IN WRN MN...THE ENVIRONMENT WILL BECOME
INCREASINGLY UNSTABLE WITH MLCAPE OF 2000-2500 J/KG.  NAM GUIDANCE
AGAIN APPEARS TO BE TOO UNSTABLE OWING TO EXCESSIVE LOW-LEVEL
MOISTURE WITH 2-M DEW POINTS INTO THE UPPER 70S AND UNREALISTIC
FORECAST SOUNDING STRUCTURES DEPICTING SHALLOW SATURATED LAYERS WITH
NEAR DRY ADIABATIC LAPSE RATES IN THE IMMEDIATE PRE-FRONTAL
ENVIRONMENT.

CONSENSUS MODEL GUIDANCE INDICATES STRONGEST WINDS ALOFT WILL SPREAD
ENEWD ALONG THE SRN PERIPHERY OF THE AFOREMENTIONED UPPER LOW...BUT
LIKELY LAGGING THE SURFACE COLD FRONT.  NEVERTHELESS...IT APPEARS
THAT SUFFICIENT EFFECTIVE SHEAR OF 30-35 KT ALONG AND JUST AHEAD OF
THE FRONT ACROSS MN WILL PROMOTE ORGANIZED MAINLY MULTICELL/BRIEF
SUPERCELL STORM STRUCTURES ESPECIALLY DURING THE LATE AFTERNOON AND
EVENING ALONG/AHEAD OF THE COLD FRONT.  A FEW SEVERE STORMS WITH
LARGE HAIL AND DAMAGING WIND GUSTS WILL BE POSSIBLE.  ACTIVITY WILL
MOVE EWD AND SLOWLY DIMINISH IN INTENSITY AS IT SPREADS ACROSS NWRN
WI/WRN LAKE SUPERIOR AND POSSIBLY FAR WRN UPPER MI DURING THE LATE
EVENING.

OTHER STRONG STORMS ARE EXPECTED TO DEVELOP SWD INTO ERN NEB AND WRN
IA BY LATE AFTERNOON AND EVENING WITHIN THE AXIS OF STRONGER
INSTABILITY ALONG/AHEAD OF THE COLD FRONT.  WINDS ALOFT AND
ASSOCIATED VERTICAL SHEAR ARE EXPECTED TO DIMINISH WITH SWD
EXTENT...SUGGESTING A MORE LIMITED THREAT FOR SEVERE STORMS ACROSS
THIS AREA ALTHOUGH ISOLATED LARGE HAIL AND DAMAGING WINDS WILL BE
POSSIBLE.

..WEISS.. 09/05/2015




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