DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 312000
SWODY1
SPC AC 311958

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT FRI AUG 31 2012

VALID 312000Z - 011200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF UPSTATE NY/NRN
NEW ENGLAND...

...THERE IS A SLGT RISK OF SVR TSTMS PARTS OF THE MIDDLE/LOWER MS
VLY INTO MO AND THE LWR OH VLY...

...GREAT BASIN/PORTIONS OF CO RIVER VALLEY...
HAVE INTRODUCED LOW SEVERE PROBABILITIES FOR PORTIONS OF NV AND
WESTERN UT/NORTHERN AZ AS TSTMS ARE LIKELY TO CONTINUE TO INCREASE
THIS AFTERNOON...AT LEAST AN ISOLATED TO WIDELY SCATTERED
BASIS...AHEAD OF A BROAD UPPER TROUGH CENTERED NEAR THE CA COAST.
SUFFICIENT PRECIPITABLE WATER AND RELATIVELY STRONG/SOMEWHAT
INCREASING VERTICAL SHEAR MAY ALLOW FOR STRONG/POSSIBLY SEVERE TSTMS
CAPABLE OF WIND AND/OR HAIL.

...NORTHERN NY/NEW ENGLAND...
NO CHANGES TO THE REGION...REFERENCE MESOSCALE DISCUSSION 1845 FOR
SHORT-TERM DETAILS.

...MIDDLE/LOWER MS VALLEY...
SPATIAL ADJUSTMENTS /MAINLY N-NE ACROSS IL/ HAVE BEEN MADE TO THE
CATEGORICAL SLIGHT RISK...BUT OVERALL FORECAST REASONING OTHERWISE
REMAINS UNCHANGED REGARDING A TORNADO THREAT /SEE DISCUSSION BELOW/.
REFERENCE TORNADO WATCH 800.

..GUYER.. 08/31/2012

.PREV DISCUSSION... /ISSUED 1129 AM CDT FRI AUG 31 2012/

...SYNOPSIS...
ERN RIDGE/WRN TROUGH PATTERN WILL PREVAIL THIS PERIOD AS TROPICAL
DEPRESSION ISAAC MOVES SLOWLY NNE FROM AR INTO MO. SHORTWAVE TROUGH
NOW OVER CNTRL QUE WILL AMPLIFY ESE LATER TODAY/TNGT...MAINTAINING
SEASONABLY STRONG WNW FLOW OVER NEW ENGLAND. IN ADDITION...MODERATE
SW FLOW WILL PREVAIL AHEAD OF TROUGH OVER THE PACIFIC NW/NRN
RCKYS...AND ENHANCED FLOW WILL PERSIST ON THE E AND N SIDES OF
ISAAC. OTHERWISE...DEEP FLOW OVER MUCH OF THE NATION WILL BE WEAK.

ANY ORGANIZED SVR THREATS THIS PERIOD SHOULD REMAIN CONFINED TO
UPSTATE NY/NRN NEW ENGLAND IN ASSOCIATION WITH QUE UPR IMPULSE...AND
WITH REMNANTS OF ISAAC.

...NRN NY/NEW ENGLAND TODAY/EARLY TNGT...
SATELLITE SHOWS QUE SHORTWAVE TROUGH...AND LEAD SPEED
MAX NOW SE ONT...CONTINUING TO PROGRESS ESE TOWARD UPSTATE NY/NEW
ENGLAND. ASSOCIATED COLD FRONT ATTM EXTENDS FROM SRN LK HURON ENE TO
THE ST LAWRENCE VLY...AND SHOULD CONTINUE ESE INTO NY/CNTRL NEW
ENGLAND BY MID EVE. MOISTURE OVER SLIGHT RISK AREA WILL REMAIN
LIMITED...BUT WILL SOMEWHAT INCREASE AS A RESULT OF MOISTENING BY
ELEVATED SHOWERS/STORMS WITH LEAD IMPULSE...AND VIA ADVECTION FROM
THE W.

WHILE SPARSE MOISTURE AND CLOUDS WITH LEAD IMPULSE WILL SOMEWHAT
LIMIT INSTABILITY...A NARROW EML WILL BE PRESENT ACROSS THE
REGION...MORE OR LESS PARALLEL TO THE COLD FRONT. UPLIFT ALONG THE
FRONT...GRADUAL INCREASE IN MOISTURE...AND SFC HEATING SHOULD
SUPPORT DEVELOPMENT OF SCTD TSTMS THIS AFTN...MOST LIKELY IN SE
ONT/SRN QUE. THIS ACTIVITY SHOULD CONTINUE MOVING/DEVELOPING ESE
INTO NRN NY/NRN NEW ENGLAND A BIT LATER IN THE DAY AS LARGER SCALE
TROUGH AMPLIFIES TOWARD REGION. DEEP...SEASONABLY STRONG /45-60 KT
WINDS IN THE 700-500 MB LAYER/ WNW FLOW MAY FOSTER BOTH SUPERCELLS
AND SHORT BOWING SEGMENTS...WITH AN ACCOMPANYING RISK FOR DMGG WIND
AND HAIL. AN ISOLD TORNADO ALSO MAY OCCUR...BUT
LOW-LVL SHEAR/MOISTURE/BUOYANCY EACH WILL BE RATHER MARGINAL FOR
A SUSTAINED TORNADO THREAT. THE STORMS SHOULD WEAKEN BY MID EVE WITH
LOSS OF DAYTIME HEATING.

...LWR MS VLY INTO MO/IL TODAY/TNGT WITH REMNANTS OF ISAAC...
REMNANT CIRCULATION OF ISAAC IS CENTERED NEAR HARRISON /HRO/ IN NW
AR ATTM. THE LOW SHOULD CONTINUE NNE INTO MO THROUGH TNGT...REACHING
THE COLUMBIA AREA BY 12Z SAT. WHILE AREA VWP DATA SHOW ASSOCIATED
WIND FIELD CONTINUING TO GRADUALLY WEAKEN...AMPLE FLOW WILL REMAIN
PRESENT TO SUPPORT ORGANIZED/SUSTAINED CONVECTION/SUPERCELLS INTO
TNGT.

CLOUDS WILL LIMIT SFC HEATING IN CORRIDOR OF OVERLAP BETWEEN
ENHANCED LOW-LVL SHEAR AND THE NW EDGE OF THE SFC MOISTURE AXIS.
NEVERTHELESS...IN THIS ZONE...MOST LIKELY EXTENDING FROM SE AR/W
CNTRL MS NWD INTO E CNTRL MO...WRN TN...WRN KY...AND SRN IL...A FEW
ROTATING STORMS MAY DEVELOP. POTENTIAL WILL BE GREATEST THIS AFTN
INTO EARLY TNGT IN ANY AREAS OF LOCALLY-ENHANCED SFC-BASED
INSTABILITY. STRONGER/MORE DISCRETE STORMS IN THIS ENVIRONMENT COULD
POSE A TORNADO RISK...WITH THE THREAT BECOMING MORE ISOLD/MARGINAL
LATER TNGT.

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