B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 87
Deviation - Altitude Overshoot; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance
Weather
Climbing to cruise altitude of FL390 on speed on autopilot; when approximately at FL385; the aircraft experienced sudden heavier than moderate turbulence; but definitely not severe. Aircraft speed and vertical speed became erratic and increasing rapidly; speed just short of Maximum Mach Operating (MMO) speed and Instantaneous Vertical Speed Indicator (IVSI) just short of 6;000 FPM.In an attempt to not let aircraft overspeed and not injure flight attendants (footers were narrow) I took control of the aircraft leveled at FL396 and descended back down to FL390. Informed ATC of the deviation and the rest of the flight was uneventful.
B737-700 Captain reported he deliberately overshot his level off altitude because he was dealing with moderate turbulence and was concerned about an overspeed.