A320 FLT CREW EXPERIENCED ALTDEV DUE TO A RAPID SHIFT IN WINDS ACCOMPANIED BY MODERATE TURB AND THE AUTOPLT DISENGAGING AND A RAPID PITCH UP.

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WE WERE AT FL370; IN CRUISE WITH THE RADAR ON TILTED .75 DEGS DOWN. THERE WERE TSTMS IN THE AREA; BUT NOTHING WITHIN 40 NM. VERY SUDDENLY WE GOT A RAPID DECREASE IN OUR TAILWIND OF ABOUT 70 KTS ACCOMPANIED BY MODERATE TURB/SEVERE TURB. OUR AIRSPD SHOT UP INSTANTANEOUSLY; CAUSING THE AIRPLANE TO GO INTO HIGH SPD PROTECTION MODE. THE AUTOPLT KICKED OFF AND THE ACFT PITCHED UP AT 4500 FPM. MY FIRST CONCERN WAS FOR THE PAX. THE SEATBELT SIGN WAS OFF SINCE IT HAD BEEN MOSTLY SMOOTH PREVIOUS TO THIS SUDDEN EVENT. I GOT THE SEATBELT SIGN ON AND TOLD THE FLT ATTENDANTS TO BE SEATED. I THEN GOT THE AUTOTHROTTLES OFF (THE AUTOPLT WAS ALREADY OFF DUE TO THE HIGH SPD PROTECTION MODE). BY THIS TIME THE ACFT WAS AT ABOUT FL388 WITH AIRSPD DECREASING RAPIDLY TOWARD VLS. I LOWERED THE NOSE SLOWLY AND DSNDED BACK TO FL370 AND NOTIFIED ATC OF THE EVENT. I WAS VERY CAUTIOUS IN MY DSCNT SINCE I WASN'T SURE IF WE HAD SOMEHOW MISSED SOME DRY TOPS ON THE RADAR. ATC TOLD US IT WAS NO PROB SINCE THERE WAS NO OTHER TFC IN THE AREA. THIS EVENT WAS QUITE DISORIENTING SINCE IT HAPPENED VERY SUDDENLY WITH CONDITIONS PREVIOUS TO THE EVENT THAT WERE VERY BENIGN. ALSO; IT MADE ME REALIZE THAT THE ONLY INDICATION THAT IN SUCH AN ENVIRONMENT; IT CAN TAKE LONGER THAN YOU THINK TO DISCERN WHAT EXACTLY IS GOING ON. I'M NOT SURE WE COULD HAVE DONE MUCH MORE TO PREVENT THE EXCESSIVE ALT GAIN; AND ENSURE EVERYONE'S SAFETY IN A MORE TIMELY MANNER. WE WERE TOLD BY ATC AFTER THE EVENT THAT WE WERE PASSING THROUGH A FRONT. I THINK A BETTER REVIEW OF THE WINDS ON THE FLT PLAN MAY HAVE ALERTED ME TO EXPECT SUCH A WIND SHIFT IN THIS AREA. HOWEVER; I THINK EVEN IF I WAS ARMED WITH THIS INFO; THE SEVERITY OF THE EVENT WOULD HAVE SURPRISED ME. I WAS VERY SURPRISED AT THE VERT SPD THE ACFT WAS ABLE TO ATTAIN (4500 FPM) GIVEN THAT MY EXPERIENCE WITH THIS ACFT NEAR ITS CRUISE CEILING IS THAT IT'S CAPABLE OF ONLY 200-500 FPM WITH FULL PWR.