DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0348 AM CST TUE FEB 20 2007 VALID 231200Z - 281200Z ...PLAINS/MS VALLEY/SRN ATLANTIC SEABOARD... A VIGOROUS UPPER-LEVEL TROUGH IS FORECAST TO MOVE QUICKLY ACROSS THE WRN U.S. FRIDAY AND FRIDAY NIGHT AND INTO THE PLAINS SATURDAY. THIS IS A MUCH SLOWER SOLUTION THAN LAST NIGHTS RUN AND THE UPPER-LEVEL TROUGH/LOW IS FARTHER SOUTH. A 100 KT MID-LEVEL JET ASSOCIATED WITH THE SYSTEM WILL EJECT NEWD ACROSS THE PLAINS STATES AROUND MIDDAY ON SATURDAY. AHEAD OF THE APPROACHING TROUGH...A STRONG LOW-LEVEL JET IS FORECAST TO DEVELOP. THIS WILL TRANSPORT LOW-LEVEL MOISTURE NWD INTO OK AND KS SATURDAY AFTERNOON AS A DRYLINE MOVES EWD ACROSS THE SRN AND CNTRL PLAINS. THUNDERSTORMS APPEAR LIKELY TO DEVELOP ALONG AND EAST OF THE DRYLINE BY AFTERNOON. STRONG VERTICAL SHEAR PROFILES COMBINED WITH ENHANCED LARGE-SCALE ASCENT WILL BE FAVORABLE FOR SUPERCELLS AND TORNADOES WITH A SEVERE WEATHER EVENT UNFOLDING SATURDAY AFTERNOON AND EVENING ACROSS THE PLAINS. AS THE SYSTEM TRANSITIONS EWD INTO THE LOWER TO MID MS VALLEY SATURDAY NIGHT...A SQUALL-LINE WITH WIDESPREAD SEVERE WEATHER POTENTIAL APPEARS LIKELY. THE SEVERE THREAT MAY CONTINUE THROUGH SUNDAY ACROSS THE OH AND TN VALLEYS WITH AN ADDITIONAL THREAT POSSIBLE FROM THE CAROLINAS TO NRN FL SUNDAY NIGHT INTO MONDAY. ..BROYLES.. 02/20/2007