The SPC is forecasting ...widespread severe thunderstorms expected over parts of the northern high plains this afternoon and tonight.... Please read the latest public statement about this event.
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SPC AC 170556 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1256 AM CDT SUN JUN 17 2007 VALID 171200Z - 181200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN PLAINS THROUGH THE UPPER MS VALLEY AND GREAT LAKES REGION... ...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE NERN STATES... ...SYNOPSIS... A PROGRESSIVE ZONAL PATTERN WILL PREVAIL OVER THE NRN THIRD OF THE COUNTRY SUNDAY. SHORTWAVE TROUGH OVER SE CANADA WILL MOVE INTO THE NERN STATES SUNDAY AFTERNOON...WHILE UPPER TROUGH OVER THE PACIFIC NW ADVANCES INTO THE NRN PLAINS. E-W FRONT CURRENTLY FROM SRN MN WWD THROUGH SD INTO ERN MT WILL LIFT NWD THROUGH THE UPPER MS VALLEY AND ND DURING THE DAY. A COLD FRONT WILL ACCOMPANY THE UPPER TROUGH EWD INTO THE NRN PLAINS. A DRYLINE WILL EXTEND FROM WRN SD SWD THROUGH THE CNTRL HIGH PLAINS. ...NRN PLAINS THROUGH UPPER MS VALLEY AREA... ELEVATED STORMS WILL BE ONGOING SUNDAY MORNING WITHIN ZONE OF LIFT N OF WARM FRONT FROM PARTS OF ND EWD THROUGH NRN MN. WARM SECTOR WILL ADVANCE NWD THROUGH ND...MN AND WI IN WAKE OF THE RETREATING FRONT. MODERATE INSTABILITY IS EXPECTED AS THE BOUNDARY LAYER WARMS WITH MLCAPE FROM 1500 J/KG OVER THE UPPER MS VALLEY TO 2500 J/KG FARTHER WEST OVER THE NRN PLAINS IN PROXIMITY TO STEEPER LAPSE RATES. INCREASING SWLY FLOW IN ADVANCE OF THE UPPER TROUGH WILL ADVECT A PLUME OF WARM AIR IN THE 850-700 MB LAYER NEWD THROUGH PRE-FRONTAL WARM SECTOR FROM ERN SD INTO CNTRL AND SRN MN. THIS MAY CAP A GOOD PORTION OF THE WARM SECTOR MUCH OF THE DAY. HOWEVER...INCREASING DEEP ASCENT ASSOCIATED WITH EWD ADVANCING SHORTWAVE TROUGH WILL ENHANCE POTENTIAL FOR STORM INITIATION ALONG THE FRONT FROM ND SWD THROUGH WRN OR CNTRL SD AND NWRN NEB. OTHER STORMS MAY DEVELOP OVER THE BLACK HILLS AND THE HIGHER TERRAIN OF ERN WY. DEEP SHEAR AROUND 40 KT IN FRONTAL ZONE WILL SUPPORT THE POTENTIAL FOR SUPERCELLS AS INITIAL STORM MODE. HOWEVER...SOME STORMS MAY EVOLVE INTO LINE SEGMENTS AS THEY PROGRESS EWD. ISOLATED LARGE HAIL AND DAMAGING WIND WILL BE THE MAIN THREATS...BUT ISOLATED TORNADOES CANNOT BE RULED OUT WITH ANY SUPERCELL MODES. OTHER STORMS MAY DEVELOP ALONG ERN EDGE OF STRONGER CAP AND IN VICINITY OF RETREATING BOUNDARY FROM NRN MN SEWD INTO PARTS OF WI AS THE ATMOSPHERE DESTABILIZES. STRONGER 0-1 KM SHEAR AND WEAKER CAP IN THIS REGION WILL SUPPORT A GREATER POTENTIAL FOR SUPERCELLS WITH LOW LEVEL MESOCYCLONES AND ISOLATED TORNADOES...ESPECIALLY WITH ANY SURFACE BASED STORMS OVER NRN MN WHERE LOW LEVEL HODOGRAPHS WILL BE MAXIMIZED ON NOSE OF THE LOW LEVEL JET AND EAST OF SURFACE LOW. ...NERN STATES... AXIS OF LOWER 60S DEWPOINTS AND SURFACE HEATING WILL CONTRIBUTE TO MODERATE INSTABILITY IN PRE-FRONTAL WARM SECTOR DURING THE DAY. A COLD FRONT WILL ATTEND SHORTWAVE TROUGH AS IT ADVANCES SEWD DURING THE DAY. STORMS ARE EXPECTED TO DEVELOP ALONG AND AHEAD OF THE FRONT AS THE BOUNDARY LAYER DESTABILIZES. A BELT OF 40+ KT MID LEVEL FLOW AND COOLER MID LEVEL TEMPERATURES WILL ACCOMPANY THE UPPER TROUGH INTO THIS REGION. DEEP SHEAR OF 30 TO 40 KT WILL SUPPORT ORGANIZED MULTICELLS...AND SOME UPDRAFTS MAY ALSO DEVELOP MID LEVEL ROTATION. OVERALL THREAT COULD BE TEMPERED SOMEWHAT BY MODEST MID LEVEL LAPSE RATES. HOWEVER...THREAT WILL EXIST FOR ISOLATED DAMAGING WIND GUSTS AND HAIL WITH THE STRONGER STORMS. ...CNTRL THROUGH SRN HIGH PLAINS... STORMS WILL LIKELY DEVELOP OVER THE HIGHER TERRAIN AND SPREAD EWD WITHIN THE DEEPLY MIXED BOUNDARY LAYER OVER THE CNTRL AND SRN HIGH PLAINS. WEAKER VERTICAL SHEAR IN THIS REGION THAN FARTHER NORTH SUGGESTS THE STORMS WILL BE LESS ORGANIZED. HOWEVER...THE STRONGER STORMS MAY PRODUCE LOCALLY STRONG WIND GUSTS AND HAIL THROUGH EARLY EVENING. ..DIAL/TAYLOR.. 06/17/2007 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z