DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 012000
SWODY1
SPC AC 011958

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT SUN SEP 01 2013

VALID 012000Z - 021200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDWEST...

...20Z UPDATE...
REGARDING THE SLIGHT RISK IN THE MIDWEST...SOME SPATIAL ADJUSTMENTS
WERE MADE ALTHOUGH THE GENERAL FORECAST SCENARIO HAS NOT CHANGED.
PRIMARY/MOST PROBABLE SEVERE RISK SHOULD EXIST THIS AFTERNOON/EARLY
EVENING ACROSS DOWNSTATE PORTIONS OF IL/INDIANA AND ADJACENT KY IN
VICINITY OF OUTFLOW BOUNDARY/OLD FRONT. FOR ADDITIONAL DETAILS...SEE
MESOSCALE DISCUSSION 1826. MEANWHILE...ADDITIONAL STRONG/POSSIBLY
SEVERE TSTMS MAY DEVELOP ALONG THE ADVANCING COLD FRONT FROM EASTERN
WI/LAKE MI VICINITY INTO NORTH-CENTRAL IL. HOWEVER...THE INFLUENCE
OF SUBSIDENCE/MID-LEVEL WARMING MAY ESPECIALLY HINDER UPDRAFT VIGOR
ACROSS AREAS SUCH AS EASTERN WI...WHILE A MORE STABLE AIRMASS
EASTWARD INTO NORTHERN/CENTRAL INDIANA MAY LIMIT THE SPATIAL EXTENT
OF ANY STRONGER STORMS THAT DEVELOP NEAR THE COLD FRONT. OTHER
SPORADIC STRONG/POTENTIALLY SEVERE TSTMS WILL REMAIN POSSIBLE INTO
EARLY EVENING ACROSS THE SOUTHEAST STATES/CAROLINAS AND PERHAPS
OTHER AREAS OF THE EASTERN CONUS.

..GUYER.. 09/01/2013

.PREV DISCUSSION... /ISSUED 1127 AM CDT SUN SEP 01 2013/

...SYNOPSIS...
WHILE AN UPPER TROUGH/LOW OFF THE PAC NW COAST WILL MAKE
CONTINUED/SLOW PROGRESS TOWARD THE COAST AND YIELD AN EWD EXPANSION
IN CYCLONIC FLOW INTO THE NWRN STATES...MOST OF THE WEST WILL REMAIN
UNDER THE INFLUENCE OF A LARGE/PERSISTENT UPPER RIDGE.
MEANWHILE...BROAD CYCLONIC FLOW WILL PREVAIL OVER THE ERN HALF OF
THE COUNTRY...AS A SHORT-WAVE TROUGH SHIFTING ACROSS THE UPPER GREAT
LAKES CONTRIBUTES TO SOME AMPLIFICATION OF THE LONGER-WAVELENGTH
TROUGHING OVER THE ERN CONUS.

AT THE SURFACE...A RELATIVELY WEAK PATTERN IS EVIDENT...WITH A PRIOR
FRONT LINGERING FROM SRN NEW ENGLAND WWD ACROSS THE MIDWEST/OH
VALLEY AND A SECOND/WEAK FRONT SHIFTING SEWD ACROSS THE GREAT
LAKES/UPPER MIDWEST/CENTRAL PLAINS. THIS AREA -- EXTENDING FROM THE
NORTHEAST WSWWD ACROSS THE OH/TN/MID MS VALLEYS AND INTO THE CENTRAL
AND SRN HIGH PLAINS NEAR AND AHEAD OF THE AFOREMENTIONED FRONTS --
WILL CONTAIN THE PRIMARY AREA OF CONVECTIVE/SEVERE POTENTIAL THIS
PERIOD.

...ILLINOIS VICINITY...
SOMEWHAT CONCENTRATED WIND/HAIL RISK STILL APPEARS POSSIBLE ACROSS
THE IL VICINITY...AS LOW CLOUD COVER DISSIPATES ALLOWING
HEATING/DESTABILIZATION TO COMMENCE AHEAD OF THE WEAK/ADVANCING COLD
FRONT. WHILE THIS REGION SHOULD REMAIN NEAR THE SRN FRINGE OF
STRONGER FLOW ALOFT...SOMEWHAT GREATER INSTABILITY SHOULD EVOLVE
HERE AS OPPOSED TO AREAS FARTHER E/NE IN CLOSER PROXIMITY TO THE
UPPER SYSTEM AND ASSOCIATED STRONGER FLOW REGIME.

AT LEAST ISOLATED STORMS SHOULD DEVELOP NEAR THE FRONT AS IT MOVES
INTO THE AREA DURING THE AFTERNOON...WITH A FEW CELLS ORGANIZING
GIVEN THE AMPLE CAPE/SHEAR ENVIRONMENT CURRENTLY ANTICIPATED. AS
SUCH...A RELATIVE CONCENTRATION OF MARGINAL HAIL/WIND EVENTS MAY
MATERIALIZE -- THUS WARRANTING CONTINUATION OF THE SLIGHT RISK AREA.

...ELSEWHERE...
BENEATH A BROAD AREA OF MODERATE CYCLONIC FLOW ALOFT FROM THE
CENTRAL PLAINS EWD TO THE ATLANTIC COAST...A MOIST BOUNDARY LAYER
WILL LOCALLY DESTABILIZE WHERE POCKETS OF HEATING CAN OCCUR AWAY
FROM ONGOING PRECIPITATION/CLOUD COVER. CONVECTIVE COVERAGE IS
PROGGED TO INCREASE THROUGH THE AFTERNOON AS THIS DESTABILIZATION
OCCURS -- PRIMARILY INVOF VARIOUS FRONTAL AND CONVECTIVE BOUNDARIES
INDICATED ACROSS THIS REGION. FOCUSED AREAS OF MORE ROBUST
CONVECTION REMAIN DIFFICULT TO DISCERN WITHIN THIS BROAD/COMPLEX
REGION. STILL...LOCALLY AMPLE INSTABILITY AND MODEST SHEAR SUGGEST
A BROAD AREA OF LOW-END/ISOLATED SEVERE RISK REMAINS THE MOST
APPROPRIATE FORECAST ATTM...MOST CONCENTRATED THROUGH THE DIURNALLY
FAVORABLE LATE AFTERNOON THROUGH MID EVENING TIME FRAME.

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