Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 020601
SWODY1
SPC AC 020600

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT SUN AUG 02 2015

VALID 021200Z - 031200Z

...THERE IS AN ENH RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS MUCH OF CENTRAL AND EASTERN WISCONSIN AND LOWER MICHIGAN INTO
ADJACENT AREAS OF NORTHEASTERN ILLINOIS...NORTHERN INDIANA AND
NORTHWEST OHIO...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
UPPER MIDWEST AND GREAT LAKES REGION...

...THERE IS A MRGL RISK OF SVR TSTMS AS FAR SOUTHWEST AS PORTIONS OF
THE CENTRAL PLAINS...AND AS FAR EAST AS THE LOWER GREAT LAKES
REGION...

...SUMMARY...
SEVERE STORMS ARE EXPECTED ACROSS THE GREAT LAKES REGION TODAY.
THIS MAY INCLUDE ONE OR TWO ORGANIZED STORM CLUSTERS CAPABLE OF
GENERATING SWATHS OF POTENTIALLY DAMAGING WIND GUSTS...IN ADDITION
TO SEVERE HAIL...AND PERHAPS A COUPLE OF TORNADOES.

...SYNOPSIS...
MODELS CONTINUE TO INDICATE AMPLIFICATION WITHIN THE MID-LATITUDE
WESTERLIES ACROSS SOUTHERN CANADA AND THE NORTHERN TIER OF THE U.S.
DURING THIS PERIOD.  WITHIN THIS REGIME...THE CENTER OF A FAIRLY
BROAD AND DEEP MID-LEVEL CLOSED LOW IS FORECAST TO SHIFT SOUTH OF
HUDSON BAY INTO NORTHERN ONTARIO...AS A SIGNIFICANT PERTURBATION
CONTINUES PIVOTING AROUND ITS SOUTHWESTERN AND SOUTHERN PERIPHERY.
IN ASSOCIATION WITH THESE DEVELOPMENTS...MID/UPPER FLOW APPEARS
LIKELY TO STRENGTHEN WHILE BECOMING INCREASINGLY CYCLONIC ACROSS THE
CENTRAL CANADIAN/U.S. BORDER AREA...INCLUDING THE UPPER GREAT LAKES
REGION...EARLY TODAY...AND THROUGH MUCH OF THE REMAINDER OF THE
GREAT LAKES REGION BY LATE TONIGHT.

UPSTREAM...A LESS PROMINENT SHORT WAVE TROUGH...AND EMBEDDED
MID-LEVEL CLOSED LOW...IS FORECAST TO GRADUALLY PROGRESS INLAND
ACROSS THE BRITISH COLUMBIA COAST. BETWEEN THIS FEATURE AND THE
DOWNSTREAM SYSTEM...SHORT WAVE RIDGING MAY BUILD TO THE EAST OF THE
CANADIAN ROCKIES.  MEANWHILE...IN LOWER  LATITUDES...SUBTROPICAL
RIDGING WILL CONTINUE TO PREVAIL OVER MUCH OF NORTHERN MEXICO AND
THE SOUTHERN TIER OF THE U.S...BUT ITS CENTER MAY CONTINUE TO
GRADUALLY WEAKEN AS ONE OR TWO PERTURBATIONS MIGRATE AROUND ITS
NORTHWESTERN PERIPHERY...ACROSS THE GREAT BASIN INTO CENTRAL
ROCKIES.

FORCING FOR ASCENT ASSOCIATED WITH THESE LATTER FEATURES...IN
ADDITION TO OROGRAPHY...ARE AGAIN EXPECTED TO CONTRIBUTE TO
CONSIDERABLE THUNDERSTORM DEVELOPMENT IN THE PRESENCE OF MONSOONAL
MOISTURE...ACROSS THE NORTHERN SIERRA NEVADA AND ADJACENT PORTIONS
OF THE GREAT BASIN...AND THE EASTERN GREAT BASIN/COLORADO PLATEAU
INTO THE CENTRAL AND SOUTHERN ROCKIES AND ADJACENT HIGH PLAINS.
SUBSTANTIAL THUNDERSTORM DEVELOPMENT IS ALSO EXPECTED WITHIN A
PERSISTENT PLUME OF HIGH MOISTURE CONTENT AIR ALONG A WEAK REMNANT
FRONTAL BAND ACROSS THE SOUTHWESTERN ATLANTIC AND NORTHERN FLORIDA
INTO THE NORTHERN GULF OF MEXICO.  HOWEVER...SEVERE THUNDERSTORM
POTENTIAL IS EXPECTED TO BE MOST PROMINENT IN ASSOCIATION WITH AN
AREA OF INCREASING THUNDERSTORM DEVELOPMENT ACCOMPANYING THE UPPER
TROUGH AMPLIFICATION OVER THE GREAT LAKES REGION.

...UPPER MIDWEST GREAT LAKES REGION...
AT LEAST SCATTERED THUNDERSTORM ACTIVITY MAY BE ONGOING AT 12Z THIS
MORNING ACROSS PARTS OF THE UPPER GREAT LAKES REGION... PRIMARILY
SUPPORTED BY A ZONE OR ZONES OF LOWER/MID TROPOSPHERIC WARM
ADVECTION...IN ADVANCE OF THE COLD FRONT ASSOCIATED WITH THE
APPROACHING MID-LEVEL PERTURBATION.  THE PRIMARY WARM FRONTAL ZONE
PROBABLY WILL EXTEND ACROSS PARTS OF NORTHERN WISCONSIN... THE UPPER
MICHIGAN PENINSULA AND NORTHERN LOWER MICHIGAN PENINSULA EARLY
TODAY.  GUIDANCE HAS BEEN SUGGESTIVE THAT THIS COULD BECOME THE
FOCUS FOR AN INITIAL EVOLVING CLUSTER OF STORMS DURING THE
DAY...GENERALLY ON THE NOSE OF A PLUME OF AT LEAST MODESTLY STEEP
MID-LEVEL LAPSE RATES EMANATING FROM THE INTERMOUNTAIN WEST.

BOUNDARY LAYER DESTABILIZATION AHEAD OF THIS INITIAL CONVECTIVE
CLUSTER...ACROSS NORTHERN LOWER MICHIGAN...REMAINS A BIT UNCLEAR.
BUT...ALONG AND SOUTH OF ITS TRAILING OUTFLOW BOUNDARY...EXTENDING
WESTWARD INTO NORTH CENTRAL WISCONSIN...MODERATE TO STRONG BOUNDARY
LAYER DESTABILIZATION APPEARS LIKELY DURING THE DAY.  THIS WILL BE
SUPPORTED BY BOUNDARY LAYER MOISTENING...WITH SURFACE DEW POINTS
INCREASING THROUGH THE 60S /TO AROUND 70F+ OVER WISCONSIN/...BENEATH
STEEPENING MID-LEVEL LAPSE RATES...AS WARMER ELEVATED MIXED LAYER
AIR CONTINUES TO ADVECT EASTWARD BENEATH RELATIVELY COOL AND
INCREASINGLY CYCLONIC NORTHWEST MID-LEVEL FLOW.

IN THE PRESENCE OF INCREASINGLY SHEARED AND STRONG DEEP LAYER MEAN
WESTERLY FLOW...UP TO AROUND 40 KT IN THE LOWER TO MID
TROPOSPHERE...THE ENVIRONMENT SHOULD BECOME CONDUCIVE TO THE
EVOLUTION OF ONE OR MORE ORGANIZED MESOSCALE CONVECTIVE SYSTEMS.
THIS MAY INCLUDE SUPERCELLS INITIALLY...PARTICULARLY NEAR THE
INTERSECTION OF THE OUTFLOW BOUNDARY AND A SOUTHWARD ADVANCING COLD
FRONT ACROSS PARTS OF NORTH CENTRAL WISCONSIN.  WHILE ACTIVITY GROWS
UPSCALE AND DEVELOPS SOUTHEASTWARD ALONG THE OUTFLOW BOUNDARY
INTO/THROUGH LOWER MICHIGAN...ADDITIONAL UPSCALE GROWTH IS POSSIBLE
SOUTHWESTWARD...ALONG/AHEAD OF THE COLD FRONT...TOWARD THE
MISSISSIPPI VALLEY.

..KERR/MARSH.. 08/02/2015



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