USA Weather — Severe Weather Division
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF CENTRAL AND EASTERN NORTH DAKOTA...
...SUMMARY...
WIDESPREAD SEVERE THUNDERSTORMS ARE FORECAST THIS AFTERNOON INTO TONIGHT ACROSS MUCH OF THE GREAT PLAINS, PARTICULARLY ACROSS THE DAKOTAS, ALSO EXTENDING INTO PARTS OF THE UPPER MIDWEST. INITIAL SUPERCELL ACTIVITY WILL PRODUCE A THREAT FOR A FEW STRONG TORNADOES AND VERY LARGE HAIL, WITH QUICK ORGANIZATION INTO A LARGE SQUALL LINE YIELDING AN INCREASINGLY WIDESPREAD THREAT FOR DAMAGING WINDS IN EXCESS OF 60-80 MPH AND SEVERAL EMBEDDED TORNADOES. ISOLATED TO SCATTERED SEVERE THUNDERSTORMS PRODUCING A THREAT FOR SEVERE WIND AND HAIL WILL ALSO EVOLVE TODAY ACROSS PARTS OF THE OHIO INTO THE TENNESSEE VALLEYS.
...CENTRAL/NORTHERN PLAINS INTO THE UPPER MIDWEST...
MORNING WATER VAPOR IMAGERY SHOWS A STRONG UPPER LEVEL TROUGH EXTENDING ACROSS THE PACIFIC NORTHWEST INTO THE GREAT BASIN, WITH A NEGATIVELY TILTED EMBEDDED SHORTWAVE EXTENDING FROM SOUTHERN IDAHO INTO WESTERN COLORADO NEAR THE BASE OF THE MAIN TROUGH. THE MAIN UPPER TROUGH WILL SLOWLY TRANSLATE EASTWARD TODAY, WITH THE EMBEDDED SHORTWAVE QUICKLY EJECTING NORTHEASTWARD, REACHING THE CENTRAL AND NORTHERN HIGH PLAINS THIS AFTERNOON AND INTO THE DAKOTAS/MIDWEST BY THIS EVENING. A BROAD SURFACE LOW WILL GRADUALLY DEVELOP TODAY ACROSS THE NORTHERN PLAINS WITH A COLD FRONT/DRYLINE EXTENDING SOUTHWARD. THE SURFACE LOW WILL GRADUALLY LIFT NORTHEASTWARD INTO THE CANADIAN PRAIRIES THIS EVENING, WITH A SOUTHEASTWARD-EXTENDING WARM FRONT LIFTING INTO THE UPPER MIDWEST TONIGHT.
SOME WEAKENING CONVECTION PERSIST THIS MORNING ACROSS WESTERN KANSAS/NEBRASKA, WITH UPPER-LEVEL CIRRUS EXTENDING INTO SOUTH DAKOTA. AS THIS SHIFTS NORTHEASTWARD AND DECAYS BY NOON TODAY, A LARGE AREA OF CLEAR SKIES WILL RESULT IN SUBSTANTIAL DIURNAL HEATING INTO THE 90S OVERTOP A VERY MOIST AIRMASS, WITH DEWPOINTS IN THE UPPER 60S TO LOW 70S EXTENDING NORTH OF THE US/CANADA BORDER. VERY STEEP LAPSE RATES IN EXCESS OF 8.5 C/KM ACROSS THE REGION WILL SUPPORT A LARGE AREA OF STRONG INSTABILITY THIS AFTERNOON, WITH MLCAPE OF 3000-4500 J/KG EXPECTED TO EXTEND ACROSS THE DAKOTAS INTO CENTRAL NEBRASKA AND NORTHERN KANSAS. FORCING FOR ASCENT WILL INCREASE EARLY TO MID-AFTERNOON AS INCREASING HEIGHT FALLS OCCUR AHEAD OF THE SHORTWAVE, AND THIS SHOULD RESULT IN INITIALLY SCATTERED CONVECTIVE INITIATION QUICKLY OCCURRING ACROSS EASTERN MONTANA INTO WYOMING, SPREADING EAST NORTHEASTWARD FAIRLY QUICKLY. INTENSIFYING MID-LEVEL FLOW WITH A SOUTHERLY 40-50KT LOW-LEVEL JET DEVELOPING BY THIS TIME WILL SUPPORT INCREASINGLY ENLARGED, LOOPING HODOGRAPHS, WHICH WILL SUPPORT QUICK ORGANIZATION INTO MULTIPLE SUPERCELLS, WITH AN INITIAL THREAT FOR VERY LARGE HAIL, WITH THE THREAT FOR A FEW STRONG TORNADOES ALSO LIKELY DEVELOPING ESPECIALLY AS STORMS MOVE INTO THE WESTERN AND CENTRAL DAKOTAS LATE THIS AFTERNOON WHERE LOWER DEWPOINT DEPRESSIONS EXIST.
AS CONVECTIVE COVERAGE BECOMES WIDESPREAD, RAPID UPSCALE GROWTH AND ORGANIZATION INTO A LARGE MCS IS EXPECTED TO OCCUR BY EARLY EVENING AS THE COLD FRONT BEGINS TO MOVE SLOWLY EASTWARD. WITH STRONG INSTABILITY REMAINING DOWNSTREAM, IN ADDITION TO INTENSIFYING SHEAR TO OVER 50-60KT AND SRH OF 250-350 M2/S2 BEING COMMON, NUMEROUS ORGANIZED BOWING SEGMENTS AND EMBEDDED CIRCULATIONS ARE EXPECTED ALONG THE LINE AS IT RACES EAST NORTHEAST ACROSS THE NORTHERN PLAINS THIS EVENING. THE HIGHLY FAVORABLE THERMODYNAMIC PROFILES ALONG WITH INCREASED COLD POOLING WILL BE SUPPORTIVE FOR WIDESPREAD DAMAGING WINDS WITH GUSTS IN EXCESS OF 75MPH LIKELY. ADDITIONALLY, SEVERAL EMBEDDED TORNADOES ARE LIKELY ESPECIALLY ACROSS CENTRAL TO NORTHERN NORTH DAKOTA, WHERE MULTIPLE CAMS SUGGEST A LARGE NW TO SE ORIENTED SEGMENT OF THE MCS WILL RACE NORTHEASTWARD WITHIN FAVORABLE ORIENTED SHEAR VECTORS. ADDITIONAL CONVECTIVE DEVELOPMENT IS EXPECTED LATER IN THE EVENING AHEAD OF AND TO THE SOUTH OF THE MCS. INTENSE SHEAR AND INSTABILITY WILL SUPPORT A MIX OF SUPERCELLS AND ORGANIZED STORM CLUSTERS, WITH ALL SEVERE HAZARDS EXPECTED TO PREVAIL WITH THIS ACTIVITY THROUGH THE END OF THE PERIOD AS IT SPREADS INTO THE UPPER MIDWEST.
...SOUTHERN PLAINS INTO NEW MEXICO...
A RELATIVE VORTICITY MAX WILL MOVE ACROSS NEW MEXICO THIS AFTERNOON INTO THE SOUTHERN PLAINS THIS EVENING, WITH A DRYLINE EXTENDING ACROSS THE HIGH PLAINS. A FAIRLY UNSTABLE AIRMASS DUE TO VERY ROBUST SURFACE HEATING AND STEEP LAPSE RATES SHOULD DEVELOP THIS AFTERNOON. AS THE VORTMAX PASSES OVERHEAD, ISOLATED TO SCATTERED HIGH-BASED DEVELOPMENT WILL OCCUR ACROSS NEW MEXICO, SPREADING NORTHEAST DURING THE AFTERNOON AND EVENING HOURS INTO THE SOUTHERN PLAINS, WITH ADDITIONAL DEVELOPMENT ALSO EXPECTED ALONG THE DRYLINE. MODERATE TO STRONG SHEAR, INCLUDING LENGTHY HODOGRAPHS WILL SUPPORT ORGANIZED LINE SEGMENTS, WITH A DEEPLY MIXED BOUNDARY LAYER ALLOWING FOR AN INCREASING THREAT OF DAMAGING OUTFLOW/DOWNBURST WINDS, A FEW OF WHICH LIKELY EXCEEDING 75MPH. FAIRLY NUMEROUS COVERAGE SHOULD EVENTUALLY EVOLVE ACROSS THE SOUTHERN HIGH PLAINS THIS EVENING, POTENTIALLY WITH AN ORGANIZED CLUSTER OR MCS DEVELOPING AND SPREADING NORTHEASTWARD, WITH AN ATTENDANT THREAT FOR DAMAGING WINDS EXPECTED.
...OHIO/TENNESSEE VALLEYS...
AN MCV WITH SCATTERED CONVECTION IS ONGOING THIS MORNING ACROSS THE OHIO INTO TENNESSEE VALLEYS. A VERY MOIST AIRMASS WITH SURFACE DEWPOINTS IN THE MID TO UPPER 70S WILL SUPPORT ROBUST DESTABILIZATION BY THIS AFTERNOON AS FILTERED SURFACE HEATING OCCURS, WITH MLCAPE OF 2500-3000 J/KG EXPECTED TO EVOLVE. AN AREA OF MODERATE DEEP-LAYER SHEAR, WITH LOW-LEVEL SHEAR/HELICITY ALSO ENHANCED BY THE MCV, WILL SUPPORT ORGANIZATION OF SCATTERED STORM CLUSTERS THAT DEVELOP THIS AFTERNOON AND SPREAD SOUTHEASTWARD, WITH A FEW STRONGER LINE SEGMENTS AND CLUSTERS LIKELY TO EVOLVE. THIS WILL SUPPORT A THREAT FOR ISOLATED TO SCATTERED DAMAGING WINDS AND LARGE HAIL, WITH THE HIGHEST THREAT EXPECTED ACROSS WEST KENTUCKY INTO CENTRAL TENNESSEE, WHERE VARIOUS CAMS SUGGEST A SMALL, ORGANIZED CLUSTER CAN DEVELOP AND RESULT IN A GREATER WIND DAMAGE THREAT THIS AFTERNOON INTO THE EVENING. ADDITIONALLY, A BRIEF TORNADO OR TWO WILL BE POSSIBLE AS A COUPLE OF TRANSIENT SUPERCELLS MAY DEVELOP WHERE ENHANCED LOW-LEVEL SHEAR AND VORTICITY DEVELOP NEAR THE MCV.