DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1145 PM CDT MON SEP 09 2013 VALID 101200Z - 111200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE NORTHEAST STATES... ...SYNOPSIS... A MID-LEVEL SHORTWAVE IMPULSE WILL MINOR OUT WITHIN CONFLUENT FLOW WHILE TRACKING FROM LAKE SUPERIOR AND ADJACENT ONTARIO INTO CNTRL/SRN QUEBEC. STRONG MID-LEVEL WSWLY FLOW ACCOMPANYING THIS DISTURBANCE WILL GLANCE THE UPPER GREAT LAKES REGION AND NEW ENGLAND...WHILE A WSWLY LOW-LEVEL JET SPREADS EWD FROM THE GREAT LAKES. AS THIS OCCURS...SFC LOW PRESSURE WILL DEVELOP EWD FROM SRN ONTARIO AND SRN QUEBEC INTO NEW ENGLAND...WITH A FRONT TRAILING SW OF THE LOW INTO THE CNTRL HIGH PLAINS. MEANWHILE...AN UPSTREAM TROUGH IN THE MID LEVELS WILL AMPLIFY INTO THE SRN CANADIAN PRAIRIE PROVINCES...MAINTAINING MEAN CYCLONIC FLOW OVER THE NRN PLAINS AND UPPER MIDWEST. A BROAD ANTICYCLONE WILL REMAIN PROMINENT OVER THE SERN/S-CNTRL CONUS...WITH FLANKING WEAK CYCLONES OVER THE LOWER CO RIVER VALLEY AND OFF THE ERN COAST OF THE FL PENINSULA. ...PORTIONS OF THE NORTHEAST STATES TODAY INTO THIS EVENING... ONE OR MORE CLUSTERS OF STRONG TO PERHAPS LOCALLY SVR THUNDERSTORMS MAY BE ONGOING AT THE BEGINNING OF THE PERIOD OVER WRN/NRN NEW YORK. THIS WOULD BE IN RESPONSE TO PRECEDING UPSCALE CONVECTIVE GROWTH WITHIN THE TERMINUS OF A 35-40-KT LOW-LEVEL JET CROSSING THE ERN GREAT LAKES. RESIDUAL NOCTURNAL INHIBITION MAY SERVE TO LIMIT THE SVR POTENTIAL THIS MORNING. HOWEVER...ISOLATED SVR WIND CANNOT BE RULED OUT DOWNWIND OF LAKES ERIE AND ONTARIO THIS MORNING AS ISALLOBARIC FORCING DRIVES RICHER LOW-LEVEL MOISTURE NEWD ACROSS THE NERN STATES...AND 30-40 KT OF UNIDIRECTIONAL CLOUD-LAYER FLOW POTENTIALLY SUPPORTS THE CONTINUATION OF ORGANIZED CONVECTION. THROUGH THE DAY...STRONGER LOW-LEVEL ASCENT ACCOMPANYING THE LLJ MAY HAVE A TENDENCY TO OUTPACE THE NEWD-EXPANDING REGION OF HIGHER THETA-E AIR SE OF THE AFOREMENTIONED SFC LOW. AT THE SAME TIME...MID-LEVEL HEIGHTS ARE FORECAST TO GRADUALLY RISE IN THE WAKE OF EARLIER CONVECTION WHOSE REMNANT DEBRIS COULD STUNT APPRECIABLE BOUNDARY-LAYER DESTABILIZATION. HOWEVER...STEEP MID-LEVEL LAPSE RATES ACCOMPANYING THE INFLUX OF AN EML PLUME WILL OVERLIE INCREASINGLY RICH BOUNDARY-LAYER MOISTURE -- E.G. SFC DEWPOINTS INTO THE 60S TO PERHAPS AROUND 70F -- TO POTENTIALLY GENERATE LARGE CONVECTIVE INSTABILITY ACROSS THE SLIGHT-RISK AREA. LATER-DAY CONVECTIVE REDEVELOPMENT CANNOT BE RULED OUT INVOF RESIDUAL OUTFLOW BOUNDARIES/DIFFERENTIAL HEATING ZONES...AND STRONG VERTICAL SHEAR WILL AID IN A CONDITIONAL POTENTIAL FOR PRIMARILY SVR WIND/HAIL. ANY SUCH ACTIVITY WOULD HAVE A TENDENCY OF SPREADING EWD/ESEWD ACROSS PORTIONS OF NEW YORK AND NEW ENGLAND BEFORE BECOMING INTERRUPTED BY THE INFLUX OF A STABLE MARINE LAYER CLOSER TO THE COAST. HOWEVER...RELATIVELY WEAK ASCENT THROUGH A DEEP LAYER AND LARGE UNCERTAINTY IN THE EVOLUTION OF NOCTURNAL CONVECTION AND ITS ENSUING IMPACT ON BOUNDARY-LAYER STATIC STABILITY BREED LOW CONFIDENCE IN THE EVOLUTION OF LATER GENERATIONS OF CONVECTION...IF ANY. IN FACT...IT IS POSSIBLE THAT MUCH...IF NOT ALL...OF THE REGION WOULD BE VOID OF DIURNAL CONVECTIVE REDEVELOPMENT. ...SERN NEB AND ADJACENT FAR NRN KS NEWD INTO WI THIS AFTERNOON AND EVENING... LIFT EMANATING FROM VERTICAL CIRCULATIONS ALONG THE SWWD-EXTENDING FRONT WILL AUGMENT ASCENDING BRANCHES OF PBL CIRCULATIONS ON THE WARMER SIDE OF THE BOUNDARY TO PROMOTE ISOLATED TO WIDELY SCATTERED THUNDERSTORMS. INSTABILITY WILL BE RATHER MARGINAL...THOUGH THE PRESENCE OF 20-45 KT OF 500-MB FLOW -- HIGHEST NORTH -- SHOULD OFFER SUFFICIENT DEEP SHEAR FOR A FEW SUSTAINED CELLS WITH THE POTENTIAL FOR ISOLATED SVR WIND. DEEP FORCING FOR ASCENT AND LIMITED BUOYANCY WILL BE THE PRIMARY FACTORS TO INHIBIT THE OVERALL SVR POTENTIAL. ...PORTIONS OF THE SOUTHWEST STATES THIS AFTERNOON AND EVENING... SCATTERED CONVECTION WILL ONCE AGAIN FORM AROUND THE WEAK MID-LEVEL CYCLONE AMIDST RESIDUAL MONSOONAL MOISTURE. STRONG WIND GUSTS WILL BE POSSIBLE IN AREAS THAT EXPERIENCE STRONGER SFC HEATING/STEEPER LOW-LEVEL LAPSE RATES. AN ISOLATED MARGINALLY SVR WIND GUST CANNOT BE RULED OUT. HOWEVER...THE PRESENCE OF ONLY MODEST MID-LEVEL FLOW/DEEP SHEAR AND ONLY MODESTLY STEEP MID-LEVEL LAPSE RATES PRECLUDE THE DELINEATION OF SVR WIND PROBABILITIES AT THIS TIME. ..COHEN/GUYER.. 09/10/2013
Posted on: Tue, 10 Sep 2013 12:04:56 +0000
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