DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1254 AM CDT MON AUG 08 2016 VALID 091200Z - 101200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN MT INTO SWRN ND AND NWRN SD... ...THERE IS A MRGL RISK OF SVR TSTMS FROM THE NRN PLAINS THROUGH THE UPPER MS VALLEY AREA... ...SUMMARY... A FEW STRONG TO SEVERE STORMS ARE POSSIBLE OVER A PORTION OF THE NORTHERN PLAINS LATE TUESDAY AFTERNOON AND EVENING WITH LARGE HAIL AND DAMAGING WIND GUSTS THE PRIMARY THREATS. A MARGINAL RISK FOR A COUPLE OF STRONG TO SEVERE STORMS WILL EXIST OVER A PORTION OF THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES DURING THE AFTERNOON. ...SYNOPSIS... UPPER LOW NOW SITUATED OVER THE PACIFIC NW IS FORECAST TO DRIFT SLOWLY EWD THROUGH THE NRN ROCKIES AND INTO WRN MT TUESDAY NIGHT. LOW-AMPLITUDE SYNOPTIC REGIME WILL EXIST DOWNSTREAM...INCLUDING A RIDGE BUILDING THROUGH NRN PLAINS IN WAKE OF A SHORTWAVE TROUGH THAT WILL MOVE THROUGH THE UPPER MS VALLEY BEFORE GLANCING THE NRN GREAT LAKES. AT THE SFC A COLD FRONT WILL MOVE INTO NRN/CNTRL MN EXTENDING WWD INTO THE NRN PLAINS. HOWEVER...TRAILING PORTION OF THIS BOUNDARY WILL LIKELY STALL OVER NRN SD BEFORE LIFTING NWD AS A WARM FRONT TUESDAY NIGHT AS A LEE LOW DEVELOPS OVER THE HIGH PLAINS OF SERN MT. A LEE TROUGH WILL EXTEND SWD THROUGH THE CNTRL HIGH PLAINS. ...DAKOTAS... IT STILL APPEARS WEAK FORCING FOR ASCENT WITH SHORTWAVE RIDGING ALOFT AND A CAPPING INVERSION ASSOCIATED WITH EML PLUME SHOULD LIMIT EXTENT OF THUNDERSTORM DEVELOPMENT MUCH OF THE DAY OVER THIS REGION. EWD EXPANSION OF EML PLUME WILL PROMOTE MODERATE INSTABILITY NEAR STALLED FRONT WHERE SFC DEWPOINTS WILL RANGE FROM THE 50S IN SERN MT TO LOW-MID 60S F FARTHER EAST ACROSS SD. A FEW STORMS MIGHT INITIATE DURING THE LATE AFTERNOON WITHIN ZONE OF DEEPER MIXING AND CONVERGENCE JUST EAST OF SFC LOW AND SOUTH OF STALLED FRONT ALONG LEE TROUGH FROM SERN MT INTO WRN SD. HOWEVER...THE BEST CHANCE FOR MORE WIDESPREAD THUNDERSTORM DEVELOPMENT WILL BE DURING THE EVENING INTO THE OVERNIGHT WHERE THE STRENGTHENING LLJ WILL AUGMENT CONVERGENCE/ISENTROPIC ASCENT ALONG/NORTH OF THE WARM FRONT. ANY ACTIVITY DEVELOPING DURING THE EARLY EVENING SHOULD BE SFC-BASED. ELY LOW-LEVEL WINDS VEERING TO WLY AND INCREASING TO 40 KT AT 500 MB WILL RESULT IN SUFFICIENT VERTICAL SHEAR FOR A FEW SUPERCELLS WITH INITIAL STORMS. WITH TIME MOST STORMS SHOULD BECOME INCREASINGLY ELEVATED NORTH OF WARM FRONT WITH A GRADUAL DECREASE IN SEVERE THREAT...THOUGH A FEW STORMS MIGHT STILL BE CAPABLE OF PRODUCING HAIL. ...WRN THROUGH CNTRL MT... GRADIENT BETWEEN EVOLVING LEE LOW AND SFC HIGH PRESSURE BUILDING DOWN FROM SRN CANADA WILL CONTRIBUTE TO ELY LOW-LEVEL WINDS OVER NRN HALF OF MT. MODEST MOIST ADVECTION SHOULD HELP TO MAINTAIN BOUNDARY-LAYER DEWPOINTS IN THE 40S TO NEAR 50F 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. DIABATIC HEATING OVER THE MOUNTAINS AND INCREASING LARGE-SCALE ASCENT DOWNWIND OF THE APPROACHING UPPER LOW SHOULD FOSTER THUNDERSTORM DEVELOPMENT OVER THE HIGHER TERRAIN DURING THE AFTERNOON. STORMS WILL SUBSEQUENTLY SPREAD EWD INTO THE HIGH PLAINS OF CNTRL MT DURING THE EVENING. INVERTED-V BOUNDARY LAYERS AND STRONG EFFECTIVE SHEAR WILL SUPPORT POTENTIAL FOR A FEW HIGH-BASED SUPERCELLS...BUT STORMS MAY EVENTUALLY EVOLVE INTO CLUSTERS AS THEY ADVANCE EWD/NEWD. ISOLATED LARGE HAIL AND DAMAGING WIND WILL BE POSSIBLE DURING THE EVENING. ...NWRN WI AND CNTRL MN... HEIGHT RISES IN WAKE OF SHORTWAVE TROUGH THAT WILL MOVE THROUGH THIS REGION EARLY IN THE PERIOD WILL LIMIT DEEP FORCING ALONG SWD ADVANCING COLD FRONT. SOUTH OF THE FRONT...THE ATMOSPHERE SHOULD BECOME MODERATELY UNSTABLE WITH 30-40 KT UNIDIRECTIONAL 0-6 KM VERTICAL SHEAR. WEAK FORCING ALOFT AND A CAPPING INVERSION IS EXPECTED TO LIMIT EXTENT OF THUNDERSTORM DEVELOPMENT IN THIS REGION. HOWEVER...AN ISOLATED STRONG TO SEVERE STORM OR TWO CANNOT BE RULED OUT ALONG THE FRONT DURING PEAK AFTERNOON HEATING. ..DIAL.. 08/08/2016Read more
from SPC Forecast Products http://ift.tt/GB0aDL
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