B737-700
Flight Crew Last 90 Days 239; Flight Crew Type 239
Distraction; Situational Awareness
Deviation - Speed All Types
Flight Crew Became Reoriented
Human Factors; Weather
In a newer model aircraft; the autothrottle disconnected and would not reengage.  During cruise at FL380 in turbulence; the speed increased rather suddenly to Mach .83 and the Airspeed Warning Clacker sounded.  The thrust was reduced and aircraft speed was brought back within limits.  It was a busy phase of flight as we were in the process of having to divert.  After landing; Dispatch and Maintenance were notified and a logbook entry was made.This might have been avoided altogether by selecting a slightly lower cruise Mach speed; or a lower altitude; but more vigilance by both pilots would have been the only way to prevent this overspeed.
Enroute to diversion airport (for weather) crew of B-737 exceeded limit speed after the autothrottle disengaged and created an overspeed situation.