DAY 3 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0230 AM CDT SUN AUG 07 2016 VALID 091200Z - 101200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER NRN SD AND SRN ND... ...THERE IS A MRGL RISK OF SVR TSTMS OVER MUCH OF THE NRN PLAINS... ...SUMMARY... A FEW STRONG TO SEVERE STORMS WILL BE POSSIBLE OVER A PORTION OF THE NORTHERN PLAINS TUESDAY AFTERNOON AND EVENING WITH LARGE HAIL AND DAMAGING WIND GUSTS THE PRIMARY THREATS. ...SYNOPSIS... MODELS HAVE CONVERGED ON SIMILAR SOLUTIONS THROUGH DAY 3 REGARDING EVOLUTION OF UPPER TROUGH NOW OVER THE PACIFIC NW. THIS FEATURE IS FORECAST TO DRIFT SLOWLY EWD THROUGH THE NRN ROCKIES EARLY TUESDAY AND INTO NWRN MT TUESDAY NIGHT. LOW-AMPLITUDE SYNOPTIC REGIME WILL EXIST DOWNSTREAM...INCLUDING A RIDGE BUILDING THROUGH THE NRN PLAINS IN WAKE OF A SHORTWAVE TROUGH THAT WILL MOVE FROM THE UPPER MS VALLEY BEFORE GLANCING THE NRN GREAT LAKES. AT THE SFC A COLD FRONT WILL MOVE INTO NRN MN EXTENDING WWD INTO THE NRN PLAINS. HOWEVER...TRAILING PORTION OF THIS BOUNDARY WILL LIKELY STALL OVER NRN SD AS LEE LOW DEVELOPS OVER THE HIGH PLAINS OF SERN MT. A LEE TROUGH WILL EXTEND SWD THROUGH THE CNTRL HIGH PLAINS. ...DAKOTAS... WEAK FORCING WITH SHORTWAVE RIDGING AND A CAPPING INVERSION MAY LIMIT THUNDERSTORM DEVELOPMENT MUCH OF THE DAY OVER THIS REGION. HOWEVER...THE ATMOSPHERE SHOULD BECOME MODERATELY UNSTABLE IN VICINITY OF STALLED BOUNDARY WHERE MID-UPPER 60S F DEWPOINTS WILL RESIDE BENEATH STEEP LAPSE RATES ASSOCIATED WITH EML PLUME. BEST CHANCE FOR STORMS TO DEVELOP WILL BE LATE AFTERNOON OR EARLY EVENING OVER SWRN ND OR NWRN SD WHERE THE STRENGTHENING LLJ WILL AUGMENT CONVERGENCE/ISENTROPIC ASCENT ALONG/NORTH OF STALLED FRONT. THE EARLY ACTIVITY MAY BE NEAR SFC BASED. ELY LOW-LEVEL WINDS VEERING TO WLY AND INCREASING TO 40 KT AT 500 MB WILL CONTRIBUTE TO SUFFICIENT SHEAR FOR A FEW SUPERCELL STRUCTURES WITH INITIAL STORMS. HOWEVER...ACTIVITY MAY EVENTUALLY EVOLVE INTO AN MCS AS IT CONTINUES EWD. LARGE HAIL AND DAMAGING WIND WILL BE THE MAIN THREATS...BUT A TORNADO OR TWO WILL BE POSSIBLE WITH INITIAL DEVELOPMENT. ...CNTRL THROUGH NERN MT... GRADIENT BETWEEN EVOLVING LEE LOW AND SFC HIGH PRESSURE BUILDING DOWN FROM SRN CANADA WILL CONTRIBUTE TO ELY LOW-LEVEL WINDS OVER ERN MT. THE MODEST MOIST ADVECTION SHOULD HELP TO MAINTAIN BOUNDARY-LAYER DEWPOINTS IN THE 40S TO NEAR 50 OVER ERN MT BENEATH PLUME OF STEEP LAPSE RATES...RESULTING IN 500-1000 J/KG MLCAPE. A BELT OF STRONGER WINDS ALOFT /40-45 KT AT 500 MB/ ASSOCIATED WITH UPPER LOW CIRCULATION WILL SLOWLY SPREAD EWD THROUGH CNTRL MT AND CONTRIBUTE TO 40+ KT EFFECTIVE BULK SHEAR. A FEW STORMS MAY BE IN PROGRESS OVER WRN MT WITHIN ZONE OF ASCENT ASSOCIATED WITH UPPER LOW CIRCULATION. DIABATIC HEATING OVER THE MOUNTAINS SHOULD FOSTER ADDITIONAL STORMS DURING THE AFTERNOON WHICH SHOULD SUBSEQUENTLY SPREAD EWD INTO THE HIGH PLAINS OF CNTRL MT. INVERTED-V BOUNDARY LAYERS AND STRONG EFFECTIVE SHEAR WILL SUPPORT POTENTIAL FOR HIGH-BASED SUPERCELLS...BUT STORMS MAY EVENTUALLY GROW UPSCALE INTO FORWARD-PROPAGATING CLUSTERS AS THE ADVANCE EWD. ISOLATED LARGE HAIL AND DAMAGING WIND WILL BE POSSIBLE THROUGH EVENING. SLIGHT RISK MIGHT BE EXPANDED WWD FOR THIS REGION IN THE UPCOMING DAY 2 OUTLOOK. ..DIAL.. 08/07/2016Read more
from SPC Forecast Products http://ift.tt/GAMjPN
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