A300
Flight Crew Air Transport Pilot (ATP)
Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance
Weather
Cruise altitude of FL330. ATC had advised of weather ahead. We were unable to paint anything on radar. We both looked outside several times and were unable to see any build ups. It was a moonless night. I saw we were headed into a build up just seconds prior to entering it. I disconnected the auto pilot and auto throttles to better manage the event. We were in the build up for probably 20 seconds. During that time we encountered significant up and down drafts; in addition to moderate turbulence. We had an altitude excursion of approximately +200 feet and -500 feet. Once out of the buildup; we resumed level flight at FL 330 and advised ATC of what had happened.We flew into a build up that we were unable to display on radar or see visually. The night being moonless probably contributed.Suggestions: Honestly I do not know. ATC advised of weather ahead of us. We did our best to find it on radar; but were unable. We also made a concerted effort to see it visually; but with no luck.
A300 Captain reported he was advised by ATC of weather ahead that the crew was unable to see on radar which resulted in an altitude excursion above and below assigned altitude due to turbulence.