Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 010555
SWODY1
SPC AC 010554

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT MON SEP 01 2014

VALID 011200Z - 021200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM LOWER MI AND SERN WI
THROUGH THE MIDWEST...MID MS VALLEY TO ERN KS AND FAR NERN OK...

...SUMMARY...
ISOLATED TO SCATTERED SEVERE THUNDERSTORMS SHOULD DEVELOP ALONG AND
AHEAD OF A WEAK COLD FRONT FROM PARTS OF THE SOUTHERN GREAT LAKES
REGION SOUTHWESTWARD ACROSS INDIANA...ILLINOIS...MISSOURI INTO
EASTERN KANSAS AND FAR NORTHEAST OKLAHOMA.  DAMAGING WINDS AND LARGE
HAIL WILL BE POSSIBLE WITH THE STRONGEST STORMS...WHILE A TORNADO
CANNOT BE RULED OUT ACROSS THE SOUTHWESTERN EXTENT OF THE SLIGHT
RISK AREA. A FEW STRONG WIND GUSTS WILL BE POSSIBLE THIS AFTERNOON
ACROSS FAR EASTERN WYOMING INTO PARTS OF SOUTHERN SOUTH DAKOTA AND
NORTHERN NEBRASKA.

...LOWER MI/SERN WI TO MID MS VALLEY TO SERN KS/NERN OK...
A PROGRESSIVE SHORTWAVE TROUGH IS EXPECTED TO TRACK NEWD FROM THE
UPPER MS VALLEY THROUGH THE UPPER GREAT LAKES EARLY IN THE FORECAST
PERIOD...REACHING ONTARIO AND WRN QUEBEC BY LATE AFTERNOON/EARLY
EVENING.  ALTHOUGH THE STRONGEST 500-MB HEIGHT FALLS /60-90 M/ ARE
FORECAST TO SPREAD THROUGH THE NRN EXTENT OF THE UPPER GREAT
LAKES...30-60 METER FALLS SHOULD OCCUR ACROSS THE ERN WI AND LOWER
MI PORTION OF THE SLIGHT RISK AREA.  MEANWHILE...AN UPSTREAM
SHORTWAVE TROUGH AND ATTENDANT SPEED MAX ARE EXPECTED TO MOVE FROM
THE CENTRAL ROCKIES THROUGH THE CENTRAL PLAINS THIS AFTERNOON TO THE
MIDWEST AND SRN GREAT LAKES LATER MONDAY NIGHT.

A COLD FRONT ASSOCIATED WITH THE LEAD SHORTWAVE TROUGH IS EXPECTED
TO EXTEND FROM WRN LAKE SUPERIOR SSWWD THROUGH CENTRAL IA INTO
CENTRAL KS AT 12Z.  THIS BOUNDARY WILL ADVANCE TO A POSITION FROM
ERN UPPER MI THROUGH SERN IA INTO SERN KS AND NORTH CENTRAL OK TO
THE TX PANHANDLE BY LATE AFTERNOON.  FRONTAL CONVECTION WILL LIKELY
BE ONGOING AT THE BEGINNING OF THE PERIOD...ENHANCED PRIMARILY BY
ASCENT AHEAD OF THE UPPER MS VALLEY SHORTWAVE TROUGH.  ADDITIONAL
STORMS MAY ALSO BE ONGOING AT DAYBREAK ACROSS ERN KS INTO CENTRAL/
SRN MO WITHIN A LOW-LEVEL WAA REGIME. GUSTY WINDS AND ISOLATED HAIL
MAY OCCUR WITH THE EARLY MORNING ACTIVITY...THOUGH GREATER TSTM
COVERAGE AND SEVERE WEATHER THREAT WILL BE POSSIBLE ACROSS THE
SLIGHT RISK AREA LATER TODAY.

STRONGEST BOUNDARY-LAYER HEATING SHOULD OCCUR ACROSS SERN KS/SWRN MO
AND OK WHERE SURFACE TEMPERATURES WILL WARM INTO THE 90S.  AS A
RESULT...INSTABILITY IS EXPECTED TO BE GREATEST ALONG THE TRAILING
PORTIONS OF THE FRONT WHERE THE ERN EXTENT OF STEEP LAPSE RATES WILL
CONTRIBUTE TO MODERATE-STRONG INSTABILITY /MLCAPE 2000-3000 J PER
KG/.  DESPITE WEAKER MIDLEVEL LAPSE RATES AND SOME UNCERTAINTY IN
DEGREE OF SURFACE HEATING...DUE IN PART TO EARLY DAY CONVECTIVE
DEBRIS...MODERATE INSTABILITY SHOULD ALSO DEVELOP ENEWD FROM MO TO
LOWER MI.

NEW TSTM DEVELOPMENT SHOULD OCCUR FROM SERN WI INTO LOWER MI AND ERN
IA TO INDIANA FROM LATE MORNING INTO THE AFTERNOON IN VICINITY OF
THE COLD FRONT AND ANY DIFFERENTIAL HEATING BOUNDARIES ATTENDANT TO
EARLY MORNING CONVECTION.  A 50-60 KT SWLY MIDLEVEL JET ACCOMPANYING
THE LEAD TROUGH WILL RESULT IN STRENGTHENING BULK SHEAR FOR THE
POTENTIAL FOR ORGANIZED STORMS PRODUCING DAMAGING WINDS AND HAIL.
MEANWHILE...TSTMS ARE EXPECTED TO BACK-BUILD SWWD THROUGH MO TO SERN
KS DURING THE MID-LATE AFTERNOON AS THE CAP WEAKENS.  LOW-LEVEL
WINDS WILL REMAIN BACKED TO SLY INTO SERN KS...NERN OK AND SWRN MO
ENHANCING CONVERGENCE INTO THE COLD FRONT AND POTENTIAL OUTFLOW
BOUNDARY FROM EARLY MORNING STORMS.  STRENGTHENING WLY MIDLEVEL
WINDS ACROSS KS/MO BY LATE AFTERNOON WILL RESULT IN STRONG BULK
SHEAR FOR ORGANIZED STORMS INCLUDING SUPERCELLS WITH THE STRONG
INSTABILITY SUPPORTING THE POTENTIAL FOR VERY LARGE HAIL AND STRONG
WIND GUSTS.  THE AFOREMENTIONED ZONE OF BACKED LOW-LEVEL WINDS WILL
ENHANCE LOW-LEVEL SHEAR FOR A TORNADO THREAT INTO THE EARLY EVENING.

...ERN WY/SWRN SD AND WRN/CENTRAL NEB...
A FAST-MOVING MIDLEVEL IMPULSE IS EXPECTED TO TRACK ESEWD FROM THE
NRN ROCKIES TO THIS DISCUSSION AREA BY LATE THIS AFTERNOON.  DESPITE
SURFACE DEW POINTS IN THE 40S...STEEP LAPSE RATES...WITH 500-MB
TEMPERATURES AROUND -15 C ACCOMPANYING THE IMPULSE...WILL RESULT IN
MARGINAL INSTABILITY /MLCAPE 500-1000 J PER KG/ THIS AFTERNOON.
TSTMS ARE EXPECTED TO DEVELOP WITHIN THIS NORTHWEST FLOW REGIME WITH
LOCALLY STRONG WIND GUSTS BEING THE PRIMARY THREAT.

..PETERS/DEAN.. 09/01/2014



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