A CPR JET EXPERIENCES A 1000 FT ALT EXCURSION AT FL340 DURING A TURB ENCOUNTER.

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WE WERE ON THE AIRWAY Q100 AT FL340 IN IMC. OUR AIRPLANE RADAR WAS ON AND WORKING; BUT SHOWED NO ECHOES. WE WERE ENCOUNTERING MOSTLY CONTINUOUS LIGHT; OCCASIONAL MODERATE CHOP. ZHU ADVISED THAT THERE WAS A STRONG ECHO OF HVY PRECIP DIRECTLY IN FRONT OF US; BUT THAT WE MAY BE ABOVE IT. OUR RADAR SHOWED NOTHING. WHEN WE QUERIED ATC ABOUT DIFFERENT ALTS; ATC SAID THE RIDE RPTS AT FL360 WERE THE SAME AND FL380 WAS BETTER BUT ANOTHER ACFT MADE HDG CHANGES TO GET AROUND WX. SHORTLY THEREAFTER; THE PLANE WAS HIT WITH A FEW SECONDS OF INTENSE RAIN THEN A HARD UPDRAFT THAT KNOCKED THE AUTOPLT OFF. THE PLANE STARTED RAPIDLY CLBING WHEN I PUT MY L HAND ON THE YOKE TO LOWER THE NOSE TO SLIGHTLY BELOW THE ARTIFICIAL HORIZON AND WITH MY R HAND REDUCE PWR. IN RETROSPECT; I SHOULD HAVE REDUCED ALL THE PWR TO HELP COUNTERACT THE BALLOONING OF THE UPDRAFT; BUT I INSTEAD MOVED MY R HAND ALSO ON THE YOKE TO HELP KEEP A LEVEL AND SLIGHTLY NOSE DOWN ATTITUDE. EVEN WITH A SLIGHTLY NOSE DOWN ATTITUDE; THE PLANE CONTINUED TO CLB TILL WE WERE APPROX 1000 FT ABOVE ASSIGNED ALT. THE PLANE FINALLY STARTED A DSCNT AND WE WERE BACK TO FL340 AND ON COURSE IN A VERY BRIEF PERIOD OF TIME. DURING THE UPDRAFT; ATC CALLED TO SAY THEY SEE US APCHING FL350 TO WHICH THE OTHER PLT RESPONDED BY SAYING WE WERE CAUGHT IN AN UPDRAFT BUT WE ARE NOW ABLE TO MAKE OUR WAY DOWN TO FL340. WE HAD NO OTHER INTENSE OR SEVERE WX AFTER THAT EXCEPT FOR LIGHT CHOP. WE HEARD ATC PASS ALONG THE INFO OF THE UPDRAFT TO OTHER CREWS BEHIND US ON Q100. OUR ACFT HAD NO PROBS WITH THE UPDRAFT EXCEPT FOR THE AUTOPLT BEING KNOCKED OFF.