B747-400
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation - Track / Heading All Types; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Object; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control
Weather
At FL360 (flight planned altitude) and approximately at 64W; Sigmet 2; 3 and 4 had been received by New York Oceanic. Our route of flight placed us in between the reported Sigmets. After questioning via ACARS; Dispatch reported our route did not show any weather and that we were clear of what they could see. We were only experiencing occasional light turbulence. One Sigmet was located North and the other South of our position. We plotted the latitude and longitude locations of the Sigmets on our iPads; showing a clear path for our route. With the electrical activity north; we changed range; tilt and sensitivity on our radar; looking for returns. I kept my radar at 40 miles or less and the SIC having his range at a greater distance. We turned down cockpit lighting looking for any clouds ahead. All looking clear and only an undercast was observed. We were operating at Mach .82; clear sky above and what appeared to be a low level undercast (appeared greater than 5;000 feet below us); PIC radar was set to 40 miles and the SIC was set at 80 miles. We could visually see lightening far off to the North and neither ND radar was painting any returns/weather. We encountered severe turbulence; momentarily losing control; the aircraft rolled left; lost 500 feet of altitude and airspeed increased into an over speed of approximately 10 knots (received an EICAS message). I (PIC) was able to quickly regain control of the aircraft and reported the encounter to NY Oceanic and Dispatch. Approximately 10 minutes after the severe turbulence; the undercast had risen to just below us (we had already requested FL380 but was denied due to traffic) (perhaps within 1;000 feet above the undercast at this point); the aircraft had not entered the cloud layer and neither radar was painting any weather in our vicinity. We observed Saint Elmo's fire; followed by what appeared to be a lightning strike from below. Deviating left or right of course would have headed us towards the electrical activity and Sigmet areas. All of this (severe turbulence and lightning strike) occurred in a time frame of approximately 10 minutes with a clear sky above; an undercast below and electrical activity north of us. The remainder of the flight was in smooth air and without further incident. PIC was in left seat; SIC Flying Pilot was in the bunk and SIC Relief was in the right seat during the events. Upon arrival in ZZZ; the appropriate logbook entries were made for the severe turbulence; over speed and lightning strike. Additionally; I discussed the events with Maintenance.
Pilot reported a flight where they encountered severe turbulence and a lightening strike that was not predicted and loss of control of aircraft.