A B757 ENCOUNTERED SEVERE TURBULENCE ON DEP WITH A STALL WARNING DUE TO THE HIGH PITCH ATTITUDE OF THE LIGHT ACFT DURING THE TURBULENCE ONSET.

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PREPARING TO TAXI OUT; THE WX WAS RPTED MILD: WIND 260 DEGS AT 19 KTS; 10 KM; 2000 FT BROKEN; QNH 999 MB; TEMP 7 DEGS; DEWPOINT 0 DEGS. AN ALTERNATE NOISE ABATEMENT DEP WAS REQUIRED AND BRIEFED WITH A DERATED-2 THRUST AND RELATIVELY LIGHT WT OF 116.9 LBS. THE SID AS CLRED WAS BRIEFED; AN AUTOMATIC SWITCH TO DEP CTL; ALONG WITH AUTOPLT ENGAGEMENT PRATT-ENG BASED ENGAGEMENT PROCS AND THE ALTIMETRY CHANGE FOR A TRANSITION ALT OF 8000 FT. HOWEVER; DURING TAXI TO TKOF; THE SHIP'S ON BOARD RADAR SHOWED SIGNIFICANT RETURNS IN THE VICINITY OF THE ARPT AND THE DEP CORRIDOR. UPON TURING ONTO THE RWY; AS WE WERE CLRED FOR TKOF; THE SHIP'S RADAR SHOWED WHAT APPEARED TO BE 2 SIGNIFICANT PRECIP WAVES OR POSSIBLY SQUALL LINES AHEAD ON THE DEP TRACK. THE CREW ALSO NOTICED A SUDDEN RISE IN SURFACE WIND SPD AT THEIR LOCATION ON THE RWY; AND THAT THE NEW WIND WAS NOT ALONG THE RWY HDG. WITHIN THE WIND GUSTS THERE WAS OCCURRING SIGNIFICANT PRECIP. THE CREW INFORMED THE TWR THAT THE FLT WOULD NOT TAKE OFF AT THIS TIME DUE TO THE PASSING SQUALL LINES; WOULD DELAY UNTIL THE SQUALL LINES HAD PASSED; AND WOULD BE WILLING TO VACATE THE RWY IF NEEDED. TWR ACKNOWLEDGED THE FLT'S RPT; CANCELLED TKOF CLRNC AND SAID THAT THE FLT SHOULD REMAIN IN POS ON THIS RWY; SINCE LNDG FLTS ARE ARRIVING ON ANOTHER RWY. THAT RWY IS LINED UP WITH THE WIND MORE CLOSELY THAN THIS RWY (WHICH WAS BEING USED ONLY FOR DEPS) AND SEVERAL ARRIVING FLTS CONTINUED TO A LNDG. HOWEVER; NO PIREPS OF EXTREME TURB WERE MADE ON TWR FREQ BY THESE ARRIVING FLTS NOR WERE ANY PASSED TO OUR FLT BY ATC. THE SQUALL LIKE WX CONTINUED AND APPEARED ON SHIP'S RADAR TO BE MOVING RAPIDLY FROM NNW ACROSS THE DEP CORRIDOR AND THE WINDS REMAINED HIGH. THE FLT HELD IN POS FOR A CONSIDERABLE TIME; BTWN APPROX 15-20 MINS. DURING THIS TIME THE SHIP'S RADAR SHOWED THE SQUALL LINES TO HAVE MOVED OFF TO THE S AND W OF THE DEP CORRIDOR. PRECIP HAD DECREASED CONSIDERABLY AND WIND GUSTS APPEARED TO HAVE DECREASED MARKEDLY ACCORDING TO OUR OWN OUTSIDE OBSERVATIONS. THE CREW DECIDED TO SET MAX RATED THRUST; HOWEVER; TO HAVE THE ADVANTAGE OF THRUST AVAILABLE AND DECREASE TKOF ROLL. THE DEP CORRIDOR NOW APPEARED SAFE FOR DEP AND THE CREW; BASED UPON ALL AVAILABLE DATA AND EXPERIENCE; ACCEPTED TKOF CLRNC. TKOF ROLL; LIFTOFF AND INITIAL CLB WERE NORMAL; AND LIGHT RAIN AND STEADY WINDS WERE ENCOUNTERED. HOWEVER; WITH A LIGHT ACFT WT AND MAX THRUST; A RELATIVELY HIGH NOSE ATTITUDE WAS DIRECTED BY THE FLT DIRECTOR. THEN UNEXPECTEDLY; ABOVE 1000 FT EXTREME TURB WAS EXPERIENCED. AS THE FLT APCHED 1500 FT AGL FOR THE TRANSITION FROM TKOF TO VNAV MODES; THE NOSE ATTITUDE WAS A LITTLE HIGH AND THE PLT MONITORING RECOMMENDED THAT THE PF DECREASE THE NOSE ATTITUDE FROM ABOUT 29 DEGS; BACK DOWN TOWARDS 20 DEGS. NONETHELESS; EVEN AS THE PF DID LOWER THE NOSE SLIGHTLY; AND VNAV MODE WAS SELECTED; THE FLT ENCOUNTERED EXTREME TURB AND A VERY BRIEF MOMENTARY TRANSITORY STALL WARNING INDICATION EVENT OCCURRED. AT THIS POINT THE PLT MONITORING DECIDED THAT THE MOST PRUDENT THING TO DO WAS TO TAKE TEMPORARY CTL OF THE ACFT; LOWER THE PITCH ATTITUDE TO ABOUT 22 DEGS AND PUSH THE PWR CTL LEVERS TO THE FULL PWR POS. DURING THIS TIME PERIOD THE FLT CONTINUED IN EXTREME TURB; AND THE PLT MONITORING -- NOW PF -- HELD FULL PWR AND ABOUT 22 DEGS OF PITCH AND CONTINUED A STEADY CLB AND TRANSITION TO AN AREA ABOVE AND OUT OF AND PAST THIS AREA. AS THE AREA OF EXTREME TURB WAS EXITED; THE CREW RESUMED NORMAL DEP CONFIGN AND NAV PROCS AND THE PLT MONITORING -- NOW PF -- RETURNED CTL OF THE FLT TO THE OTHER FLT CREW MEMBER. THE FLT PROCEEDED TO DEST WITHOUT ANY FURTHER REMARKABLE EVENTS. DURING THE CRUISE PORTION OF THE FLT; THE CREW HELD A DISCUSSION ON WINDSHEAR-LIKE; EXTREME TURB ENCOUNTER PROCS. IF ANY LESSON CAN BE GAINED BY THIS EVENT FROM THIS RELATIVELY PRUDENT CAPT'S VIEWPOINT; IT IS TO EXHIBIT EVEN GREATER CAUTION AND RELY ON THE SHIP'S RADAR SYS LESS TO DETERMINE POSSIBLE AREAS OF TURB AHEAD ON THE FLT PATH. EVEN THOUGH THE FLT CREW DELAYEDDEP UNTIL IT APPEARED ON SHIP'S RADAR THAT THE SQUALL AREAS HAD TRANSITED PAST THE DEP CORRIDOR; AT NIGHT THERE IS JUST NOT ENOUGH VISUAL REF TO SEE VERY FAR AHEAD INTO THE SKY; EVIDENTLY; TO MAKE A PRUDENT DETERMINATION. ALSO; THE SHIP'S RADAR EQUIP; WHILE EXCELLENT AT DISPLAYING PRECIP; IS APPARENTLY NOT AS EXCELLENT AT DISPLAYING AREAS OF EXTREME TURB. IN RETROSPECT; IT MIGHT HAVE BEEN MORE PRUDENT TO CONSIDER A FURTHER DELAY OR EVEN A BLOCK TURN-BACK; IN THIS CIRCUMSTANCE; AND EVEN MORE SO HAD IT BEEN KNOWN OR EXPECTED THAT EXTREME TURB WAS OCCURRING AT AND ABOVE 1000 FT. ALSO; I WOULD COMMENT THAT THE WINDSHEAR RECOVERY PROCS WHICH ARE TAUGHT IN OUR TRAINING; SUCH AS IN THE WINDSHEAR DEMO ON TKOF; ARE VERY USEFUL EVEN WHEN A SHORT AND ACCELERATED STALL IS ENCOUNTERED DUE TO EXTREME TURB; EVEN IF THAT EVENT OCCURRED AT AN ALT ABOVE 1000 FT.