USA Weather — Severe Weather Division
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS THE TENNESSEE VALLEY...
...SUMMARY...
SEVERE THUNDERSTORMS ARE EXPECTED FROM THE OHIO VALLEY AND TENNESSEE VALLEY SOUTHWARD INTO THE LOWER MISSISSIPPI VALLEY. MULTIPLE STRONG TO INTENSE TORNADOES, WIDESPREAD DAMAGING WINDS, AND VERY LARGE HAIL ARE ALL EXPECTED.
...SYNOPSIS...
A LARGE UPPER TROUGH EXTENDING OVER THE CENTRAL PLAINS INTO THE OZARKS IS NOTED ON MORNING WATER VAPOR IMAGERY. THIS TROUGH WILL CONTINUE TO ADVANCE EASTWARD TO NORTHEASTWARD BEFORE FLATTENING OUT WITH A BELT OF ZONAL FLOW EXTENDING ACROSS THE MIDDLE CONUS TOWARDS THE END OF THE PERIOD. A BROAD SURFACE CYCLONE OVER THE CENTRAL PLAINS WILL GRADUALLY SHIFT NORTHEASTWARD INTO THE UPPER MS VALLEY BY THIS AFTERNOON, PROGRESSING EASTWARD THEREAFTER. A COLD FRONT EXTENDING SOUTH OF THE LOW WILL GRADUALLY ADVANCE EASTWARD THROUGH THE PERIOD.
...OHIO/TENNESSEE/LOWER MISSISSIPPI VALLEY...
ONGOING THUNDERSTORMS ARE NOTED FROM WESTERN KENTUCKY INTO THE MISSISSIPPI DELTA. THESE STORMS WILL GRADUALLY DECAY AS THEY SHIFT NORTHEASTWARD THIS MORNING, LEAVING AN OUTFLOW BOUNDARY DRAPED ACROSS THE MID-SOUTH IN ITS WAKE. SUBSTANTIAL LOW LEVEL MOISTURE IS EXPECTED ACROSS THE WARM SECTOR, WITH DEWPOINTS IN THE 70S REACHING AS FAR NORTH AS THE OHIO RIVER VALLEY, WITH 73-76 DEGREE DEWPOINTS POSSIBLE OVER THE MID-SOUTH INTO PARTS OF THE TENNESSEE VALLEY. MODEL SOUNDINGS INDICATE RATHER STEEP LAPSE RATES IN EXCESS OF 7.5-8.0 C/KM WITHIN THESE AREAS. ROBUST SURFACE HEATING WILL SUPPORT SUBSTANTIAL DESTABILIZATION WITH MLCAPE REACHING THE 2500-4000 J/KG THIS AFTERNOON.
AS FORCING FOR ASCENT INCREASES BY EARLY AFTERNOON IN ADDITION TO INCREASED SURFACE CONVERGENCE, DEVELOPMENT OF SCATTERED TO NUMEROUS CONVECTION IS EXPECTED, INITIALLY OVER THE MID-SOUTH. LONG, CURVING HODOGRAPHS WITH SRH IN EXCESS OF 200-300 M2/S2, PARTICULARLY NEAR THE REMNANT OUTFLOW WILL SUPPORT SEVERAL SUPERCELLS INITIALLY WITH POTENTIAL FOR MULTIPLE STRONG TO INTENSE AND PERHAPS A LONG TRACKED TORNADO, AS WELL AS DAMAGING HAIL/WIND. INCREASING DEVELOPMENT LATER IN THE AFTERNOON IS EXPECTED ALONG THE EASTWARD ADVANCING COLD FRONT, WITH UPSCALE GROWTH INTO NUMEROUS CLUSTERS AND LINE SEGMENTS EVENTUALLY EXPECTED. INCREASINGLY WIDESPREAD DAMAGING WINDS ARE EXPECTED, PARTICULARLY ACROSS THE TENNESSEE VALLEY. SEVERAL GUSTS IN EXCESS OF 75 MPH ALSO APPEAR PROBABLE GIVEN STEEP LOW-LEVEL LAPSE RATES AND INCREASING DEEP-LAYER FLOW.
DEVELOPMENT OF A SOUTHEASTWARD-PROGRESSING MCS IS EXPECTED THIS EVENING OR OVERNIGHT FROM CENTRAL TENNESSEE INTO CENTRAL MISSISSIPPI. DAMAGING WIND GUSTS WILL BE POSSIBLE ALONG MORE INTENSE SEGMENTS DUE TO FAVORABLE INSTABILITY/SHEAR. FORCING FOR ASCENT WILL WEAKEN AS STORMS PROGRESS SOUTHWARD OVERNIGHT, THUS RENDERING SEVERE POTENTIAL INCREASINGLY ISOLATED.