High Risk Today in North MS and North AL, South TN

SPC AC 070601 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0101 AM CDT FRI APR 07 2006 VALID 071200Z - 081200Z ...THERE IS A HIGH RISK OF SVR TSTMS TODAY ACROSS MUCH OF NRN MS...NRN AL...AND PARTS OF SRN TN. THIS INCLUDES THE MEMPHIS TN/TUPELO MS AREAS EASTWARD INTO BIRMINGHAM AL AND CHATTANOOGA ...WHICH SEEMS LIKELY TO BE AT THE FOCUS FOR AN OUTBREAK OF SEVERE THUNDERSTORMS...INCLUDING THE RISK FOR SUPERCELLS WITH TORNADOES.... ...THERE IS A MDT RISK OF SVR TSTMS TODAY INTO TONIGHT THROUGH A LARGE PORTION OF THE LOWER MISSISSIPPI VALLEY THROUGH THE TN VLY/SRN APPALACHIANS.... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE AND HIGH RISK AREAS...ACROSS MUCH OF THE NATION EAST OF THE MS RIVER INTO THE APPALACHIANS.... THE LARGE-SCALE UPPER FLOW PATTERN HAS BECOME A BIT LESS PROGRESSIVE...BUT MODELS INDICATE THAT THE CENTRAL PLAINS CLOSED LOW WILL GRADUALLY EVOLVE INTO AN OPEN WAVE AND TURN SOUTHEASTWARD TODAY...LIKELY ADVANCING THROUGH MUCH OF THE LOWER MISSISSIPPI VALLEY BY 12Z SATURDAY. THIS IS FORECAST IN RESPONSE TO A SIGNIFICANT SMALLER SCALE IMPULSE ROTATING AROUND ITS SOUTHWESTERN/SOUTHERN PERIPHERY...AND FORCING ASSOCIATED WITH A NORTHERN STREAM TROUGH...WHICH WILL DIG THROUGH THE GREAT LAKES REGION. AS THIS OCCURS...A BROAD BELT OF STRONG CYCLONIC MID/UPPER FLOW IS PROGGED TO CONTINUE TO GRADUALLY OVERSPREAD MUCH OF THE GULF COAST STATES AND MID SOUTH INTO THE NORTHEAST. STRENGTHENING WIND FIELDS/SHEAR PROFILES WILL BECOME JUXTAPOSED WITH A RETURN FLOW OF BOUNDARY LAYER MOISTURE FROM THE WESTERN GULF OF MEXICO...THROUGH A BROAD AREA FROM THE LOWER/MIDDLE MISSISSIPPI VALLEY INTO THE APPALACHIANS. THIS IS EXPECTED TO SUPPORT INCREASING CONVECTIVE POTENTIAL...INCLUDING RISK FOR SEVERE STORMS...WHICH COULD BECOME FAIRLY NUMEROUS AND INTENSE BY THE AFTERNOON/EVENING HOURS. OTHER THUNDERSTORM ACTIVITY APPEARS POSSIBLE INTO CENTRAL PACIFIC COASTAL AREAS. APPROACHING UPPER TROUGH IS FORECAST TO GENERALLY REMAIN OFFSHORE...BUT MODELS INDICATE A FAIRLY SIGNIFICANT IMPULSE WILL PIVOT AROUND ITS EASTERN PERIPHERY...ACROSS THE CALIFORNIA COAST THROUGH THE SIERRA NEVADA BY THE END OF THE FORECAST PERIOD. ...LOWER MISSISSIPPI VALLEY THROUGH SOUTHERN APPALACHIANS... MODELS SUGGEST LEADING EDGE OF MID-LEVEL COOLING ASSOCIATED WITH THE PLAINS SYSTEM WILL OVERSPREAD MUCH OF THE REGION BY MID DAY. THIS WILL WEAKEN INHIBITION...AND SURFACE HEATING MAY BE ENOUGH TO INITIATE AT LEAST SCATTERED VIGOROUS CONVECTIVE DEVELOPMENT AS BOUNDARY LAYER DEW POINTS CLIMB THROUGH THE 60S. AS MIXED LAYER CAPE INCREASES IN EXCESS OF 2000 J/KG...STRONG DEEP LAYER SHEAR WILL BE SUPPORTIVE OF SUPERCELLS. CONFLUENT REGIME ASSOCIATED WITH 30 TO 40 KT SOUTHWESTERLY LOW-LEVEL JET SEEMS A LIKELY FOCUS FOR ACTIVITY...FROM PARTS OF CENTRAL/SOUTHERN MISSISSIPPI THROUGH EASTERN TENNESSEE. SOME OF THESE SUPERCELLS MAY BECOME LONG-LIVED...AND MODELS SUGGEST SUBSTANTIALLY LARGE/CLOCKWISE CURVED HODOGRAPHS ALONG THIS AXIS TO SUPPORT POTENTIAL FOR A FEW STRONG TORNADOES. WITH THE APPROACH OF DIGGING UPPER TROUGH...STRENGTHENING MID/UPPER FORCING IS EXPECTED TO SUPPORT INCREASINGLY WIDESPREAD SEVERE THUNDERSTORMS FROM THE LOWER MISSISSIPPI VALLEY INTO MIDDLE TENNESSEE LATE THIS AFTERNOON INTO THE EVENING HOURS. ACTIVITY MAY BE SLOW TO WEAKEN AS STRONGER FORCING SHIFTS TOWARD THE SOUTHERN APPALACHIANS OVERNIGHT. ...OHIO VALLEY... DEFORMATION ZONE BETWEEN NORTHERN AND SOUTHERN STREAM IMPULSES APPEARS TO BE A LIKELY FOCUS FOR CONVECTIVE DEVELOPMENT TODAY. MODELS SUGGEST FAIRLY STRONG SURFACE HEATING WILL OCCUR ALONG AN AXIS FROM THE ST. LOUIS AREA EASTWARD THROUGH SOUTHERN OHIO... WHICH SHOULD SUPPORT WEAK TO MODERATE DESTABILIZATION AHEAD OF DEVELOPING/STRENGTHENING BAROCLINIC ZONE. FRONTAL ZONE IS PROGGED TO SURGE SOUTH OF THE GREAT LAKES REGION EARLY THIS AFTERNOON... THROUGH MUCH OF THE OHIO VALLEY BY EARLY EVENING. THIS FORCING IS EXPECTED TO BECOME SUFFICIENT FOR AN EVOLVING SQUALL LINE...WITH MIXED LAYER CAPE ON THE ORDER OF 1000 J/KG SUPPORTIVE OF VIGOROUS UPDRAFTS IN STRONG AND SHEARED WESTERLY FLOW. IN ADDITION TO LARGE HAIL...DAMAGING WIND GUSTS COULD BECOME FAIRLY NUMEROUS BY/ SHORTLY AFTER PEAK HEATING. ..KERR/CROSBIE.. 04/07/2006