Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 040458
SWODY2
SPC AC 040456

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1156 PM CDT FRI JUL 03 2015

VALID 051200Z - 061200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE SUNDAY AFTERNOON AND
EVENING ACROSS PARTS OF CENTRAL AND NORTHERN NEBRASKA...SOUTHERN AND
EASTERN SOUTH DAKOTA AND ADJACENT PORTIONS OF SOUTHEASTERN NORTH
DAKOTA/WEST CENTRAL AND SOUTHWESTERN MINNESOTA...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
NORTH CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
THUNDERSTORMS CAPABLE OF PRODUCING SEVERE WIND AND HAIL ARE EXPECTED
SUNDAY ACROSS PARTS OF NEBRASKA...SOUTH DAKOTA AND ADJACENT PORTIONS
OF THE NORTHERN PLAINS.

...SYNOPSIS...
MID/UPPER SUBTROPICAL RIDGING APPEARS LIKELY TO REMAIN AT LEAST
SOMEWHAT SUPPRESSED DURING THIS PERIOD...BUT LINGERING CYCLONIC FLOW
ALOFT NOW PRESENT ACROSS THE SOUTH CENTRAL INTO SOUTHEASTERN U.S.
MAY BECOME INCREASINGLY CONFINED TO THE VICINITY OF A REMNANT WEAK
CIRCULATION OVER THE LOWER OHIO/TENNESSEE VALLEYS AND
CENTRAL/SOUTHERN APPALACHIANS.  STRONGER MID-LATITUDE WESTERLIES ARE
EXPECTED TO REMAIN CONFINED TO THE NORTHERN TIER OF THE
U.S...NORTHWARD...WITH SIGNIFICANT EMBEDDED POSITIVELY TILTED
TROUGHING FORECAST TO PROGRESS EASTWARD ACROSS THE CENTRAL CANADIAN
PROVINCES...AND TO THE LEE OF THE NORTHERN U.S. ROCKIES.

THERE HAS BEEN CONSIDERABLE SPREAD AMONG THE MODELS AND THEIR
RESPECTIVE ENSEMBLE OUTPUT CONCERNING LOWER/MID TROPOSPHERIC
DEVELOPMENTS RELATED TO THIS LATTER FEATURE.  EMBEDDED SMALLER SCALE
PERTURBATIONS MAY GROW INCREASINGLY OUT OF PHASE...WITH PERHAPS THE
MAIN IMPULSE ACCELERATING TOWARD THE HUDSON/JAMES BAY REGION...WHILE
A LESSER TRAILING IMPULSE DIGS ALONG THE MONTANA/ NORTH DAKOTA
INTERNATIONAL BORDER AREA.

AN ASSOCIATED SURFACE COLD FRONT STILL APPEARS LIKELY TO ADVANCE
SOUTHWARD TO THE LEE OF THE NORTHERN AND CENTRAL ROCKIES...AND
EASTWARD ACROSS THE NORTHERN PLAINS...INTO PORTIONS OF THE UPPER
MISSISSIPPI VALLEY AND MID MISSOURI VALLEY BY 12Z MONDAY.  MODELS
CONTINUE TO INDICATE THAT STRONG DESTABILIZATION WILL TAKE PLACE
WITHIN A CORRIDOR AHEAD OF THIS FRONT...AND THIS IS EXPECTED TO
PROVIDE THE PRIMARY FOCUS FOR THE MOST SUBSTANTIVE CONVECTIVE
POTENTIAL ACROSS THE U.S. SUNDAY AFTERNOON INTO SUNDAY EVENING.
THIS WILL INCLUDE THE RISK FOR THUNDERSTORM ACTIVITY CAPABLE OF
PRODUCING SEVERE WIND GUSTS AND HAIL.

...NORTH CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY...
MODELS REMAIN SUGGESTIVE THAT AN INITIAL MID/UPPER JET STREAK MAY
PROGRESS EAST MOSTLY TO THE NORTH OF THE INTERNATIONAL BORDER...
WHILE A TRAILING...AND PERHAPS STRENGTHENING...SPEED MAXIMUM LAGS TO
THE WEST OF THE COLD FRONT TO THE SOUTH.  DEEP LAYER SHEAR AHEAD OF
THE COLD FRONT OVER THE U.S. MAY NOT BECOME PARTICULARLY STRONG.
HOWEVER...STEEPENING OF MID-LEVEL LAPSE RATES ASSOCIATED WITH THE
NORTHEASTWARD ADVECTION OF ELEVATED MIXED LAYER AIR... COUPLED WITH
PRE-FRONTAL BOUNDARY LAYER MOISTENING...ARE EXPECTED TO CONTRIBUTE
TO LARGE MIXED LAYER CAPE /2000-3000+ J PER KG/ BY LATE SUNDAY
AFTERNOON.

THE STRENGTH OF MID-LEVEL INHIBITION THROUGH THE AFTERNOON REMAINS
UNCLEAR...BUT GUIDANCE GENERALLY SUGGESTS THAT LARGE-SCALE FORCING
FOR ASCENT WILL BECOME SUFFICIENT TO AT LEAST CONTRIBUTE TO THE
INITIATION OF STORMS BY EARLY SUNDAY EVENING...IF NOT BEFORE.
PERHAPS AIDED BY THE INFLUENCE OF ANOTHER MORE SUBTLE MID/UPPER
IMPULSE...MIGRATING AROUND THE NORTHERN PERIPHERY OF THE SUBTROPICAL
RIDGING...STRONGEST UPPER DIVERGENCE HAS BEEN CONSISTENTLY FORECAST
TO OVERSPREAD PORTIONS OF NORTHERN NEBRASKA/SOUTHERN AND EASTERN
SOUTH DAKOTA THROUGH THE 06/00-06Z TIME FRAME.

GIVEN THE ANTICIPATED THERMODYNAMIC PROFILES...LARGE HAIL AND SEVERE
WIND GUSTS WILL BE POSSIBLE IN THE MOST VIGOROUS STORMS.  ACTIVITY
COULD GRADUALLY CONSOLIDATE INTO A MORE SUBSTANTIVE CLUSTER OF
STORMS DURING THE EVENING...AIDED BY FORCING FOR ASCENT ASSOCIATED
WITH INCREASING LOW-LEVEL WARM ADVECTION.

..KERR.. 07/04/2015




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