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| Probabilistic Tornado Graphic | |||||||||
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| Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point. |
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| Probabilistic Damaging Wind Graphic | |||||||||
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| Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point. |
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| Probabilistic Large Hail Graphic | |||||||||
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| Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point. |
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SPC AC 182000 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0300 PM CDT WED SEP 18 2013 VALID 182000Z - 191200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM SD...ERN ND INTO NWRN MN... ...DAKOTAS INTO NWRN MN... HAVE MADE ADJUSTMENTS TO ONGOING FORECAST...PRIMARILY TO ACCOUNT FOR HIGH BASED STORMS IN THE PROCESS OF DEVELOPING OVER ERN WY INTO WRN SD. DEEP MIXING OF THE BOUNDARY LAYER IS IN PROGRESS ACROSS WRN SD WHERE TEMPERATURES HAVE WARMED INTO THE UPPER 80S TO LOW 90S AND WINDS HAVE SHIFTED TO WLY IN PRE-FRONTAL WARM SECTOR UPSTREAM FROM A TROUGH AXIS/WARM FRONT LOCATED ACROSS THE ERN DAKOTAS. STORMS WILL REMAIN RELATIVELY HIGH BASED AS DEWPOINTS MIX DOWN INTO THE 40S...BUT SUFFICIENT INSTABILITY 500-800 J/KG MLCAPE IN PRESENCE OF 30-40 KT UNIDIRECTIONAL WLY SHEAR TO SUPPORT SOME SUPERCELL STRUCTURES. ACTIVITY IS EXPECTED TO SPREAD EWD ACROSS THE WRN HALF OF SD BEFORE DIMINISHING LATER THIS EVENING. THE ATMOSPHERE STILL APPEARS CAPPED...BUT OTHER STORMS MAY DEVELOP FARTHER EAST WITHIN CONFLUENT FLOW REGIME ACROSS ERN SD LATER THIS EVENING. FARTHER NORTH...STRATUS HAS PREVENTED BOUNDARY LAYER DESTABILIZATION OVER ERN ND INTO NRN MN. HOWEVER...ELEVATED STORMS MAY DEVELOP FARTHER NORTH WITHIN ZONE OF WARM ADVECTION AND ISENTROPIC LIFT ACROSS ERN ND INTO NRN MN WITH A THREAT FOR MAINLY HAIL. ..DIAL.. 09/18/2013 .PREV DISCUSSION... /ISSUED 1116 AM CDT WED SEP 18 2013/ ...SERN MT INTO WY... A STRONG UPPER TROUGH IS MOVING ACROSS MT/ID/WY TODAY...AND WILL EMERGE INTO THE NORTHERN HIGH PLAINS TONIGHT. MID LEVEL HEIGHT FALLS AND INCREASING FORCING FOR ASCENT WILL ALSO OVERSPREAD MUCH OF THE NORTHERN AND CENTRAL PLAINS BEGINNING THIS EVENING...FOSTERING THE DEVELOPMENT OF SCATTERED THUNDERSTORMS. CONVECTION WILL LIKELY DEVELOP BY MID-LATE AFTERNOON FROM SOUTHEAST MT INTO EASTERN WY AS UVVS BEGIN TO AFFECT THE WESTERN EDGE OF SUFFICIENT LOW LEVEL MOISTURE AND INSTABILITY. EFFECTIVE SHEAR VALUES OF 30-40 KNOTS WILL PROMOTE A FEW ROTATING STORMS CAPABLE OF HAIL AND GUSTY WINDS. HOWEVER...SPARSE LOW LEVEL MOISTURE IS EXPECTED TO LIMIT COVERAGE OF STORMS AND OVERALL SEVERE THREAT IN THESE REGIONS. ...EASTERN DAKOTAS/WESTERN MN... BY EARLY EVENING...THE THREAT OF THUNDERSTORMS WILL INCREASE OVER PARTS OF EASTERN ND/NORTHEAST SD INTO WESTERN MN. RICHER LOW LEVEL MOISTURE AND STRONG INSTABILITY WILL BE PRESENT IN THIS REGION...BUT A CAPPING INVERSION WILL ALSO BE PRESENT. MOST MODEL SOLUTIONS SHOW AT LEAST ISOLATED CONVECTION FORMING ALONG/AHEAD OF APPROACHING SURFACE LOW AND FRONT. ANY STORM THAT FORMS COULD BECOME SUPERCELLULAR AND BE CAPABLE OF HAIL AND DAMAGING WINDS. THUS HAVE MAINTAINED THE SLIGHT RISK AREA. ...WESTERN SD/NEB... DURING THE EVENING...STORMS WILL PROGRESS EASTWARD FROM WY INTO THE WESTERN DAKOTAS AND NEB. STEEP LOW LEVEL LAPSE RATES AND SLOWLY COOLING THERMODYNAMIC PROFILES ALOFT MAY CONTINUE TO SUPPORT ISOLATED STRONG TO OCCASIONALLY SEVERE STORMS AFTER DARK. CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z |