SD Under the Gun STP =8 CAPE=6000 Uncapped with Gravity Waves
Posted by JAC on 5/22/2010, 4:34 pm
    MESOSCALE DISCUSSION 0662 NWS STORM PREDICTION CENTER NORMAN OK 0151 PM CDT SAT MAY 22 2010 AREAS AFFECTED...PORTIONS OF WRN/CENTRAL SD AND ND CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY VALID 221851Z - 222015Z A TORNADO WATCH IS LIKELY FOR PORTIONS OF THE WRN/CENTRAL DAKOTAS BY MID AFTERNOON. AT 18Z...WEAK AREAS OF LOW PRESSURE WERE LOCATED IN ERN MT AND SWRN SD...WITH A WEAK FRONT/TROUGH CONNECTING THE TWO LOW PRESSURE SYSTEMS. FROM THE LOW IN SRN SD...A WARM FRONT STRETCHED EWD THROUGH THE CENTRAL PORTIONS OF THE STATE. AN ISOLATED SEVERE STORM WAS LOCATED IN NRN ND IN REGION OF STRONG LOW LEVEL JET/WARM ADVECTION. THE UPDRAFT OF THIS STORM IS SITUATED AROUND 850 MB AND GIVEN THE STABLE BOUNDARY LAYER...HAIL WILL BE THE PRIMARY THREAT AS IT MOVES NEWD. HOWEVER...WATER VAPOR IMAGERY AND MODEL GUIDANCE SHOW AN UPPER WAVE AND JET MAX WILL BE MOVING NEWD FROM WY INTO THE WRN DAKOTAS LATER THIS AFTERNOON. THESE FEATURES SHOULD AID IN CONVECTION DEVELOPING OVER THE HIGHER TERRAIN OF NERN WY AND THEN SPREADING INTO THE WRN/CENTRAL DAKOTAS LATER THIS AFTERNOON/EVENING. THE AIR MASS EAST AND SOUTH OF THE PRE-MENTIONED FRONTS WAS VERY UNSTABLE WITH MLCAPES NEAR 3000 J/KG. THIS INSTABILITY PLUS EFFECTIVE SHEAR AROUND 60 KT WILL BE VERY FAVORABLE FOR INTENSE SUPERCELLS. THOUGH VERY LARGE HAIL IS EXPECTED TO BE THE PRIMARY THREAT...THE MOISTENING BOUNDARY LAYER AND STRONG LOW LEVEL SHEAR...ESPECIALLY NEAR THE WARM FRONT...WHICH WILL BE LIFTING SLOWLY NWD TOWARD THE SD/ND BORDER..WILL SUPPORT TORNADOES. EXTENSIVE CLOUDS AND WEAKER INSTABILITY WILL PERSIST NORTH OF WARM FRONT AND THOUGH THIS MAY LIMIT THE NWD EXTENT OF SEVERE WEATHER SOMEWHAT...ELEVATED SUPERCELLS WITH LARGE HAIL ARE ALSO EXPECTED NORTH OF THE WARM FRONT. ..IMY.. 05/22/2010  MESOSCALE DISCUSSION 0663 NWS STORM PREDICTION CENTER NORMAN OK 0309 PM CDT SAT MAY 22 2010 AREAS AFFECTED...SWRN SD AND WRN NEB CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 222009Z - 222145Z IF STORMS IN SERN WY CAN BE MAINTAINED NEWD AND ACQUIRE STRONG UPDRAFTS...A WW WOULD BE REQUIRED FOR PORTIONS OF WRN NEB AND SWRN SD. A SURFACE LOW WAS LOCATED IN NRN SD...WEST OF MBG...WITH A SURFACE TROUGH EXTENDING SWWD THROUGH THE NEB PANHANDLE AND INTO SERN WY. SOME WEAK CONVECTION HAD DEVELOPED DURING THE PAST HOUR IN SERN WY...POSSIBLY IN RESPONSE TO FORCING ASSOCIATED WITH AN UPPER LEVEL SPEED MAX APPROACHING THE AREA FROM THE SW. THE AIR MASS ALONG AND EAST OF THE SURFACE TROUGH WAS WELL MIXED WITH DEWPOINTS MOSTLY IN THE 50S AND TEMPERATURES NEAR 80. DESPITE STEEP MID LEVEL LAPSE RATES...THIS WELL MIXED BOUNDARY LAYER WAS RESULTING IN MOSTLY WEAK INSTABILITY WITH MLCAPES FROM 500-1500 J/KG. THE EXCEPTION WAS IN SRN SD...EAST OF RAP...WHERE SURFACE DEWPOINTS IN THE LOWER 60S WERE RESULTING IN MLCAPES BETWEEN 1500-2500 J/KG. GIVEN THE WEAK INSTABILITY...THERE IS A CONCERN WHETHER THE CONVECTION CAN BE MAINTAINED...ESPECIALLY DUE TO STRONG DEEP LAYER SHEAR AT 50 TO 60 KT. HOWEVER...IF STORMS CAN STRENGTHEN...DRY ADIABATIC LAPSE RATES FROM THE SURFACE TO 500 MB WOULD BE SUPPORTIVE OF STORMS WITH STRONG AND DAMAGING WINDS. ..IMY.. 05/22/2010 |
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- Kenny Allen - Chasing at the Missouri River, SD - JAC, 5/22/2010, 4:42 pm
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