Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 91; Flight Crew Total 15600; Flight Crew Type 5500
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence
Weather
Aircraft was in IMC conditions; just in the tops of a layer we were in at 39;000. Weather radar showed very weak; low intensity very widely scattered small returns approximately 40 NM north of our position. Without warning we were in heavy precipitation; then very pronounced turbulence; and a strong updraft that carried the aircraft very rapidly 300+ feet above our assigned altitude. Objects in the cockpit floated off the surface they were laying on; and I was hanging in my seatbelt as the autopilot returned rapidly to the assigned altitude. Encounter was reported to ATC and company dispatch. Aircraft and crew were safe and undamaged after the encounter. Ops normal the rest of the flight.
[Report narrative contained no additional information.]
B747-400 flight crew reported a strong updraft in oceanic airspace that caused a gain of 300 feet in altitude.