And I’m currently sitting bang in the middle of the enhanced risk area! There’s a 5% chance of tornadoes, which sounds low but people have seen great stuff with lesser risk
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0747 AM CDT FRI MAY 15 2015 VALID 151300Z - 161200Z ...THERE IS AN ENH RISK OF SVR TSTMS OVER SWRN/S CENTRAL SD AND WRN/CENTRAL NEB... ...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE NRN PLAINS INTO THE SRN HIGH PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS OVER SRN TX... ...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK OVER SRN TX... ...THERE IS A MRGL RISK OF SVR TSTMS FROM THE LOWER MO VALLEY TO THE LOWER GREAT LAKES... ...SUMMARY... SEVERE THUNDERSTORMS ARE EXPECTED ACROSS PARTS OF FAR NORTHEAST COLORADO...SOUTHEAST WYOMING...NEBRASKA AND SOUTHERN SOUTH DAKOTA THIS AFTERNOON AND EVENING. MORE ISOLATED STRONG/SEVERE STORM DEVELOPMENT IS POSSIBLE SOUTHWARD INTO THE SOUTHERN HIGH PLAINS BY THIS EVENING...WITH SOME INCREASE IN THREAT FROM WESTERN KANSAS INTO WEST TEXAS LATER TONIGHT. A FEW SEVERE STORMS WILL BE POSSIBLE INTO EARLY AFTERNOON OVER SOUTH TEXAS. A FEW STRONG TO ISOLATED SEVERE STORMS ARE ALSO POSSIBLE THIS AFTERNOON AND EVENING FROM PARTS OF THE MIDDLE MISSISSIPPI VALLEY EASTWARD ACROSS THE MIDWEST REGION TO THE LOWER GREAT LAKES. ...SYNOPSIS... AN EXPANSIVE UPPER LOW OVER THE PACIFIC COASTAL STATES IS FORECAST TO CONTINUE EWD REACHING THE ROCKIES BY THE END OF THE PERIOD AS A SERIES OF VORTICITY MAXIMA/SHORT WAVE TROUGHS ROTATE THROUGH THE SRN AND ERN PERIPHERY OF THE LARGE-SCALE CIRCULATION. AT THE SURFACE...A BROAD REGION OF LOW PRESSURE CURRENTLY OVER MUCH OF THE WRN STATES WILL GRADUALLY CONSOLIDATE WITH THE PRIMARY LOW DEVELOPING OVER THE CENTRAL HIGH PLAINS BY THIS EVENING...THEN MOVE NWD INTO THE NRN HIGH PLAINS BY 12Z/16. A NORTH-SOUTH DRY LINE IS FORECAST TO BECOME ESTABLISHED FROM THE HIGH PLAINS LOW SWD INTO SWRN TX BEFORE IT IS OVERTAKEN BY A PACIFIC COLD FRONT LATER TONIGHT. A WARM FRONT DEVELOPING ACROSS SRN NEB IS EXPECTED TO LIFT NWD ACROSS PARTS OF SD TONIGHT. ...NRN/CENTRAL HIGH PLAINS REGION... ELEVATED STORMS ARE OCCURRING IN A BAND FROM SWRN SD ACROSS CENTRAL NEB AND NORTH CENTRAL KS WITHIN A ZONE OF FOCUSED WARM ADVECTION. THIS ACTIVITY IS EXPECTED TO SPREAD NWD AND SLOWLY WEAKEN AS THE SOUTHERLY LOW-LEVEL JET AND ASSOCIATED THERMAL ADVECTION DIMINISHES LATER THIS MORNING. IN THE WAKE OF THESE STORMS...MOISTURE WILL SPREAD NWD AS PRESSURE FALLS INCREASE OVER WRN PARTS OF NEB AND SD...WITH SURFACE DEW POINTS IN THE 50S TO LOW 60S EXPECTED ALONG/SOUTH OF THE WARM FRONT. STEEPER MID-LEVEL LAPSE RATES /7-8 DEG PER KM/ OVER THE HIGH PLAINS COUPLED WITH MODERATE DIABATIC HEATING IN THE LOW LEVELS WILL RESULT IN AIR MASS DESTABILIZATION WITH SBCAPE REACHING 1000-2000 J/KG THIS AFTERNOON. FOCUSED LOW-LEVEL CONVERGENCE IS EXPECTED TO INCREASE THIS AFTERNOON NEAR THE SURFACE LOW AND ADJACENT WARM FRONT. THIS WILL COMBINE WITH UPSLOPE FLOW TO THE NORTH OF THE LOW AND DIVERGENCE ALOFT IN LEFT EXIT REGION OF THE UPPER-LEVEL JET AS IT ADVANCES NWD ACROSS THE SRN/CENTRAL ROCKIES TO ENHANCE UPWARD MOTION OVER THE AREA. CONSENSUS OF MESOSCALE AND CONVECTION-ALLOWING MODELS INDICATE STORMS WILL DEVELOP BY EARLY/MID AFTERNOON ACROSS SERN WY/NERN CO/NEB PANHANDLE/SWRN SD REGION WITH ACTIVITY SPREADING NEWD THROUGH THE EVENING HOURS. VEERING WIND PROFILES WITH HEIGHT...PARTICULARLY ALONG AND NORTH OF THE WARM FRONT... WILL RESULT IN SUFFICIENT DEEP-LAYER SHEAR /35-45 KT IN LOWEST 6 KM AGL/ FOR ORGANIZED STORMS TO DEVELOP INCLUDING A FEW SUPERCELLS. STRONG CELLS WILL BE CAPABLE OF PRODUCING LARGE HAIL...DAMAGING WIND GUSTS...AND A FEW TORNADOES THROUGH THE EVENING HOURS. ACTIVITY MAY DEVELOP INTO ONE OR MORE NEWD MOVING LINE SEGMENTS BY THIS EVENING WITH THE SEVERE THREAT POSSIBLY TRANSITIONING TO MAINLY DAMAGING WIND GUSTS BEFORE STORMS WEAKEN AFTER 03-06Z. ...WRN KS INTO WRN TX... ALTHOUGH THE DRY LINE IS EXPECTED TO MIX EWD DURING THE DAY...LIMITED FORCING FOR LARGE-SCALE ASCENT AND WEAK LOW-LEVEL CONVERGENCE SUGGEST STORM DEVELOPMENT WILL REMAIN ISOLATED DURING THE AFTERNOON AND EARLY EVENING. FAVORABLE INSTABILITY/STEEP LOW-MID LEVEL LAPSE RATES AND 30-40 KT VERTICAL SHEAR WILL BE SUPPORTIVE OF HAIL AND STRONG WIND GUSTS WITH ANY SUSTAINED CELL THAT FORMS. THE DRY LINE IS FORECAST TO RETREAT WWD DURING THE EVENING...AND AS THE COLD FRONT MOVES EWD AND OVERTAKES THE DRY LINE FROM NORTH TO SOUTH DURING THE NIGHT...MORE STORMS ARE EXPECTED TO INITIATE IN A BAND FROM EXTREME ERN CO/WRN KS SWD INTO PARTS OF WEST TX. VERTICAL SHEAR WILL INCREASE AS THE MID/UPPER LEVEL JET SHIFTS EWD/NEWD INTO THE SRN/CENTRAL HIGH PLAINS AND OVERSPREADS THE WRN EDGE OF THE WARM SECTOR. THE PRIMARY THREAT FROM STRONGER STORMS WILL BE DAMAGING WIND GUSTS AND LARGE HAIL INTO THE OVERNIGHT HOURS. ...SOUTH TX... A SMALL LINEAR CLUSTER OF ORGANIZED STRONG TO SEVERE STORMS HAS PERSISTED OVERNIGHT AND IS MOVING EWD INTO PARTS OF ERN LA SALLE AND NRN WEBB COUNTIES. NEW DEVELOPMENT HAS TAKEN PLACE ON THE SRN FLANK OF THE STORMS WHERE MOIST INFLOW IS PROMOTING NEW UPDRAFT FORMATION. THE STORMS ARE LOCATED DOWNSTREAM FROM A WELL-DEFINED FEATURE IN WATER VAPOR IMAGERY THAT IS PROGRESSING EWD ACROSS SWRN TX AND NRN MEXICO. THIS SUGGESTS THE ACTIVITY MAY PERSIST THROUGH THE MORNING AS IT SPREADS EWD/SEWD WITHIN AN ENVIRONMENT CHARACTERIZED BY 30-40 KT DEEP-LAYER SHEAR AND CAPE OF 1500-2500 J/KG. THIS WILL SUPPORT A THREAT FOR LARGE HAIL...DAMAGING WINDS...AND POSSIBLY A BRIEF TORNADO OR TWO GIVEN THE FAVORABLE LOW-LEVEL HODOGRAPH STRUCTURE EXHIBITED BY CRP VAD WINDS. ...LOWER MO VALLEY INTO THE LOWER GREAT LAKES... A RATHER BROAD ZONE OF CONVECTION IS FORECAST TO EVOLVE WITHIN A BACKGROUND LOW-LEVEL WARM ADVECTION REGIME...AS GRADUAL MOISTENING OF THE LOW-LEVEL AIR MASS COMBINES WITH SOME AFTERNOON HEATING TO RESULT IN AN AMPLY UNSTABLE ENVIRONMENT. STRONGEST FLOW ALOFT ACROSS THE REGION WILL LIKELY REMAIN CONFINED TO THE LOWER GREAT LAKES REGION -- WHERE WEAKEST INSTABILITY IS EXPECTED. FARTHER W...GREATER MOISTURE/INSTABILITY BUT WEAKER FLOW ALOFT SHOULD -- IN AN OVERALL SENSE -- GREATLY LIMIT ORGANIZATION POTENTIAL/SEVERE WEATHER RISK. STILL...WITH A STRONGER WIND GUST OR MARGINALLY SEVERE HAILSTONE NOT OUT OF THE QUESTION...WILL MAINTAIN AN AREA OF LOW /5%/ HAIL AND WIND SEVERE WEATHER RISK ACROSS THIS REGION. ..WEISS/LEITMAN.. 05/15/2015
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