SWODY1
SPC AC 021255
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0755 AM CDT FRI SEP 02 2011
VALID 021300Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM NEB AND IA ENE INTO
WI...NRN IL...AND MI...
...SYNOPSIS...
BROAD CYCLONIC FLOW WILL PREVAIL FROM SW CANADA AND THE NRN RCKYS
EWD INTO ONT...WRN QUE...AND THE UPR GRT LKS THROUGH EARLY
SAT...POLEWARD OF UPR HIGH CENTERS OVER THE SRN RCKYS AND THE OH
VLY. TWO IMPULSES IN THE CYCLONIC FLOW...ONE NOW OVER NRN MN AND
THE OTHER OVER NW MT...WILL IMPACT STRONG TO POTENTIALLY SVR TSTM
DEVELOPMENT THIS PERIOD.
BETWEEN THE ANTICYCLONES...UPR LOW NOW OVER THE NWRN GULF OF MEXICO
SHOULD REMAIN MORE OR LESS STNRY NEAR THE SW LA CST. THE LOW WILL
INTERACT WITH T.D. 13 THAT...ATTM...REMAINS LOOSELY ORGANIZED OVER
THE GULF S OF THE CNTRL LA CST.
AT THE SFC...COLD FRONT ASSOCIATED WITH MN IMPULSE SHOULD WEAKEN AS
IT SETTLES FARTHER SE ACROSS THE MID MS VLY/UPR GRT LKS LATER TODAY.
A NEW...STRONGER COLD FRONT WILL REACH WRN ND EARLY TNGT...IN
ADVANCE OF MT UPR DISTURBANCE. THIS FRONT SHOULD CONTINUE E/SE
ACROSS THE NRN HALF OF THE PLNS AND UPR MS VLY BY 12Z SAT.
...NEB/IA INTO WI/IL/MI TODAY THROUGH TNGT...
SEVERAL ROUNDS OF STRONG TO OCCASIONALLY SVR TSTMS EXPECTED TO
PERSIST INVOF STALLING FRONTAL ZONE FROM THE CNTRL PLNS ENE INTO
WI/IL/MI THIS PERIOD AS MOIST AXIS /PW AOA 1.75 INCHES/ PERSISTS
BENEATH BELT OF ENHANCED WSW FLOW IMMEDIATELY TOPPING OH VLY RIDGE.
IN THE NEAR TERM...IT APPEARS THAT ONGOING STRONG/SVR TSTM CLUSTER
NOW IN SW WI WILL CONTINUE TO BE ENHANCED BY ASCENT ASSOCIATED WITH
NRN MN UPR IMPULSE. THE STORMS MAY REMAIN STG/SVR ENEWD ACROSS THE
REMAINDER OF WI.
AS THE MN DISTURBANCE CONTINUES NEWD INTO ONT LATER TODAY...LARGE
SCALE FORCING WILL DIMINISH OVER THE MID/UPR MS AND MID MO VLYS.
BUT SFC HEATING AND CONTINUING PRESENCE OF FAIRLY STEEP MID LVL
LAPSE RATES/LOW LVL MOISTURE PLUME SHOULD SUPPORT SCTD AREAS OF
STORMS BY MID TO LATE AFTN ON SRN FRINGE OF FRONTAL BAND
CLOUDS...AND/OR ALONG OUTFLOW BOUNDARIES FROM OVERNIGHT
ACTIVITY...FROM ERN NEB ENE INTO IA/SRN WI AND NRN IL. GIVEN 25-30
KT WSWLY MEAN CLOUD LAYER FLOW AND SBCAPE RANGING FROM 2500-3500
J/KG...SETUP MAY SUPPORT A FEW BOWING SEGMENTS/SUSTAINED STORMS WITH
LOCALLY SVR WIND/HAIL. ADDITIONAL SPORADIC ROUNDS OF STRONG TO
POSSIBLY SVR STORMS MAY PERSIST INTO THE OVERNIGHT ACROSS MUCH THE
SAME REGION AS LLJ STRENGTHENS BOTH DIURNALLY..AND IN RESPONSE TO
THE APPROACH OF MT/ND UPR TROUGH.
...CNTRL HI PLNS THIS AFTN/EVE...
MODERATE INSTABILITY /MUCAPE TO 1500 J PER KG/ WILL DEVELOP TODAY
OVER PARTS OF THE CNTRL HI PLNS...ALONG AND N OF LEAD COLD FRONT AS
THAT BOUNDARY BECOMES STNRY AND WEAKENS OVER NW KS/ERN CO.
POST-FRONTAL MOISTURE ADVECTION/UPSLOPE FLOW...AND STRONG SFC
HEATING...SHOULD SUPPORT ISOLD TO WDLY SCTD AFTN STORMS. WEAK
NEAR-SFC WINDS WILL LIMIT MAGNITUDE OF LOW-LEVEL SPEED/DIRECTIONAL.
BUT ERN CO WILL LIE BENEATH BELT OF ENHANCED FLOW TOPPING THE SRN
RCKYS UPR RIDGE...SUPPORTING UP TO 30-40 KTS WLY CLOUD LAYER SHEAR.
THIS SETUP MAY YIELD A FEW MULTICELLS AND MARGINAL SUPERCELLS WITH
SVR HAIL AND...GIVEN DEEPLY MIXED PBL...DMGG WIND GUSTS.
...CNTRL APPALACHIANS AND ADJACENT PIEDMONT THIS AFTN/EVE...
WDLY SCTD TO SCTD TSTMS EXPECTED TO FORM WITH SFC HEATING THIS AFTN
OVER THE HIGHER TERRAIN OF THE CNTRL APPALACHIANS. DEVELOPMENT MAY
BE AUGMENTED BY CONVERGENCE ALONG WEAK WARM/STNRY FRONT STALLED OVER
THE REGION. THE STORMS SHOULD MOVE GENERALLY S WITHIN MODERATE NLY
FLOW ON WRN FRINGE OF OFFSHORE UPR TROUGH. RELATIVELY STEEP MID LVL
LAPSE RATES AND SEASONABLY STRONG MEAN FLOW MAY SUPPORT ORGANIZATION
INTO A FEW SMALL CLUSTERS CAPABLE OF LOCALLY DMGG WIND AND PERHAPS
MARGINALLY SVR HAIL THROUGH EARLY THIS EVE.
...CNTRL GULF CST LATER TODAY THROUGH TNGT...
MOIST...CYCLONICALLY CURVED LLJ SHOULD GRADUALLY STRENGTHEN OVER THE
CNTRL GULF CST REGION AS T.D. 13 GRADUALLY MOVES NWD TOWARD THE
CNTRL LA CST PER NHC. GRADUALLY ENLARGING HODOGRAPHS MAY ULTIMATELY
YIELD A CONDITIONAL TORNADO POTENTIAL GIVEN THE PRESENCE OF
SUSTAINED DISCRETE SHOWERS/STORMS. WHILE CLOUD COVER WILL LIMIT LOW
LVL DESTABILIZATION...INSTABILITY MAY BE ENHANCED BY PROXIMITY OF
UPR LOW IN THE NWRN GULF. WHILE THE TORNADO
THREAT ATTM APPEARS TOO ISOLD/CONDITIONAL FOR INTRODUCTION OF A
CATEGORICAL SVR OTLK...AN UPGRADE MAY BE NEEDED IF THE PROSPECTS FOR
DISCRETE STORMS AND SUBSTANTIAL STRENGTHENING OF T.D. 13 BECOME
APPARENT LATER TODAY.
...NRN PLNS...
ISOLD STORMS WITH A POTENTIAL FOR LOCALLY DMGG WIND MAY DEVELOP LATE
THIS AFTN THROUGH EARLY TNGT OVER WRN/NRN ND AS FORCING FOR ASCENT
INCREASES INVOF OF STRAIGHTENING COLD FRONT AHEAD OF MT TROUGH.
WHILE MOISTURE WILL BE LIMITED...STEEP LOW TO MID LVL LAPSE RATES
WILL YIELD AMPLE STATIC INSTABILITY FOR STRONG UPDRAFTS/DOWNDRAFTS.
..CORFIDI/GARNER.. 09/02/2011
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