SPC 1300Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0742 AM CDT SUN JUN 16 2013 VALID 161300Z - 171200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE CNTRL/SRN GREAT PLAINS FOR TODAY INTO TONIGHT... ...SYNOPSIS... A LOW-AMPLITUDE BELT OF MODERATE MID-LEVEL WLY/S WILL EXTEND FROM THE NRN PLAINS TO THE NE STATES DOWNSTREAM OF A RIDGE OVER THE ROCKIES. ONE EMBEDDED SHORTWAVE TROUGH WILL ADVANCE FROM THE SRN CANADIAN PRAIRIE PROVINCES TO THE GREAT LAKES...WHILE A LEADING IMPULSE TRACKS FROM THE GREAT LAKES TO NEW BRUNSWICK. A WEAK SFC COLD FRONT ACCOMPANYING THE LATTER FEATURE WILL TRACK FROM LOWER MI TO NEW ENGLAND BEFORE MOVING OFFSHORE TONIGHT. THE FRONT WILL TRAIL WWD OVER THE SRN FRINGES OF THE MODERATE WLY/S INTO THE CNTRL PLAINS. AS SFC PRESSURE FALLS COMMENCE OVER PARTS OF THE NRN PLAINS...THIS FRONT WILL ADVANCE NWD AS A WEAKENING WARM FRONT ACROSS PARTS OF NEB. MEANWHILE...A DEWPOINT GRADIENT WILL SHARPEN THIS AFTERNOON INVOF A STRENGTHENING LEE TROUGH THAT WILL EXTEND N/S OVER THE CNTRL/SRN HIGH PLAINS. ...PORTIONS OF THE CNTRL/SRN GREAT PLAINS FOR TODAY INTO TONIGHT... THE AIR MASS WILL BECOME MODERATELY TO STRONGLY UNSTABLE S OF THE WEAKENING WARM FRONT AND E OF THE LEE TROUGH THIS AFTERNOON AS STEEP MID-LEVEL LAPSE RATES ARE MAINTAINED BY THE INFLUX OF AN EML. MODIFIED 12Z RAOBS SUGGEST THAT MLCAPE VALUES ARE EXPECTED TO REACH AROUND 1500-3500 J/KG THIS AFTERNOON AS DIURNAL HEATING OCCURS AMIDST MIDDLE 60S TO LOWER 70S SFC DEWPOINTS. A FEW SCENARIOS FOR THUNDERSTORM AND ASSOCIATED SVR POTENTIAL FOLLOW: /1/ THUNDERSTORMS ARE EXPECTED TO DEVELOP BY MID AFTERNOON OVER THE CO ROCKIES AS OROGRAPHIC CIRCULATIONS STRENGTHEN THROUGH THE DAY...WITH ADDITIONAL STORM DEVELOPMENT OCCURRING ALONG THE LEE TROUGH THIS AFTERNOON. AS THIS ACTIVITY IS STEERED ESEWD INTO THE MORE BUOYANT AIR LYING E OF THE LEE TROUGH...IT SHOULD INTENSIFY WHILE POTENTIALLY CONGEALING INTO ONE OR MORE MESOSCALE CONVECTIVE SYSTEMS LATE THIS AFTERNOON INTO THIS EVENING. SVR HAIL/WINDS WILL BE POSSIBLE WITH THIS ACTIVITY...WITH THE GREATEST POTENTIAL FOR SVR HAIL INVOF A LOW-LEVEL MOIST AXIS EXTENDING INTO SWRN NEB...NWRN KS...AND NERN CO. SVR WINDS WILL BECOME OF INCREASING CONCERN AS CONVECTION POTENTIALLY GROWS UPSCALE ACROSS PORTIONS OF CNTRL/SRN KS...WITH THIS ACTIVITY PERHAPS SPREADING INTO PARTS OF NRN/WRN OK AND THE ERN TX PANHANDLE OVERNIGHT TONIGHT AT THE TERMINUS OF A MODESTLY STRENGTHENING SWLY LOW-LEVEL JET STREAM. TORNADO POTENTIAL WILL BE GREATLY LIMITED BY THE OUTFLOW-DOMINANT NATURE OF THIS CONVECTION THAT WILL LIKELY ASSUME A MORE QUASI-LINEAR MODE. /2/ ONGOING ELEVATED THUNDERSTORM DEVELOPMENT OVER THE WRN HALF OF NEB AND SD IS ASSOCIATED WITH WEAK ASCENT ACCOMPANYING A LOW-AMPLITUDE PERTURBATION WHICH RECENTLY CRESTED THE MID-LEVEL RIDGE. THIS ACTIVITY MAY PERSIST THROUGH THE DAY WHILE TRACKING ESEWD/SEWD AMIDST MODERATE MID-LEVEL FLOW SUPPORTING 30-45 KT OF EFFECTIVE BULK SHEAR. THIS ACTIVITY COULD STRENGTHEN AND PRODUCE SVR WINDS/HAIL AS IT INTERACTS WITH INCREASINGLY SFC-BASED EFFECTIVE LAYERS WITH DIURNALLY GROWING BUOYANCY S OF THE WARM FRONT. /3/ CLUSTERS OF NOCTURNAL THUNDERSTORMS HAVE ESTABLISHED AN EXTENSIVE OUTFLOW BOUNDARY WELL WITHIN THE LARGER-SCALE WARM SECTOR...ARCING FROM S-CNTRL KS TO W-CNTRL OK AND INTO THE SRN TX PANHANDLE. ONGOING STORMS N OF THIS BOUNDARY MAY WEAKEN THROUGH THE MORNING...WITH THE BOUNDARY GRADUALLY EDGING NWD THROUGH THE DAY. INVOF THIS BOUNDARY...MODIFICATIONS TO 12Z RAOBS SUGGEST THAT DIURNAL SFC HEATING MAY BE SUFFICIENT TO REDUCE MLCINH TO YIELD CONVECTIVE REDEVELOPMENT BY THIS AFTERNOON ACROSS PARTS OF SWRN KS...WRN OK...AND THE TX/OK PANHANDLES. STORMS COULD CONGEAL INTO ONE OR MORE SEWD-MOVING CLUSTERS AMIDST SOMEWHAT MORE MODEST EFFECTIVE SHEAR...AND SVR WINDS/HAIL WOULD BE POSSIBLE WITH THIS ACTIVITY. SHOULD THIS ACTIVITY BECOME MORE ORGANIZED/ABUNDANT THIS AFTERNOON/EVENING...IT WOULD REDUCE THE SVR POTENTIAL IN SUCH AREAS OVERNIGHT TONIGHT OWING TO CONVECTIVE OVERTURNING. ...EAST OF THE MISSISSIPPI RIVER FOR TODAY INTO THIS EVENING... THE FRONTAL ZONE WILL BE THE FOCUS FOR SHOWERS/STORMS THROUGH THE PERIOD. WIDESPREAD CONVECTIVE DEBRIS EXTENDS FROM THE MID-MS VALLEY TO THE NJ COAST ON THE WARM SIDE OF THIS BOUNDARY...PARTLY IN ASSOCIATION WITH A SUBTLE SHORTWAVE DISTURBANCE BEING ABSORBED INTO THE ZONE OF MODERATE WLY/S. THIS WILL LARGELY RESTRICT INSOLATION/DIABATIC HEATING IN AREAS WHERE MID-LEVEL FLOW IS ENHANCED BY THE DISTURBANCE. FURTHERMORE...SFC OBSERVATIONS AND 12Z RAOBS SUGGEST THAT THE BOUNDARY LAYER WILL NOT BECOME PARTICULARLY MOIST/UNSTABLE IN AREAS WHERE KINEMATIC PROFILES WOULD OTHERWISE SUPPORT FAST...EWD-MOVING CONVECTIVE CLUSTERS WITH SVR WIND GUSTS -- I.E. FROM PARTS OF NERN WV TO S-CNTRL PA EWD TO THE DELMARVA AND SRN NJ. WHILE SOMEWHAT GREATER INSTABILITY MAY OCCUR S OF THE MORE DENSE MULTI-LAYERED CLOUD DECK -- I.E. ACROSS PARTS OF KY AND SRN VA SWWD INTO NRN MS -- WEAKER TROPOSPHERIC FLOW IN THESE AREAS SHOULD LIMIT THE SVR POTENTIAL. ..COHEN/MEAD.. 06/16/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1300.html
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