Narrative:

Captain was in crew rest. Received SIGMET from [dispatch] about va (volcanic ash) cloud; reported to be over 100 NM north of current track. Reported previous flights had operated within SIGMET area with no issues. Crossing 180W at level 340; we were initially in and out of the tops of weather and encountered light turbulence. Continuing east; the weather began to break up; and we noticed 'distinctly grey' wisps of clouds and virga like projections.at level; it appeared as grey smog. We confirmed a slow and steady (but slight about 30-40 degrees celsius) egt rise on both engines. Re-examining our situation; we concluded a climb and an offset south would clear us from the grey haze and wispy clouds. The wind was about 140 kts. There was nothing of note depicted on the weather radar. We climbed to 350 and offset 4 NM right of course and could visually see that we were clear of the greyish layers below us. We both confirmed that the egts (exhaust gas temperature) were normal. All engine indications were normal. We continued for another 10 minutes; monitoring indications. We pressed the EICAS event marker. The weather below us continued to clear; with now only small cumulus clouds low to the surface below us. We did continue to see the grey haze layer below us also. That is when the weather radar picked up strong returns below us; and we documented the event with the pictures provided. We contacted [dispatch] with our status and location and asked dispatch to report to ATC. As we passed over the radar returns; they cleared with no further indications. The grey haze also dissipated as we continued east. The captain was informed and coordinated with [dispatch] and ATC for a precautionary divert into ZZZ. Possible flight into area of [unforeseen] volcanic ash cloud.

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Original NASA ASRS Text

Title: Air carrier flight crew and Dispatcher reported an inflight volcanic ash encounter which resulted in a diversion to the nearest suitable airport.

Narrative: Captain was in crew rest. Received SIGMET from [Dispatch] about VA (Volcanic Ash) cloud; reported to be over 100 NM north of current track. Reported previous flights had operated within SIGMET area with no issues. Crossing 180W at level 340; we were initially in and out of the tops of weather and encountered light turbulence. Continuing east; the weather began to break up; and we noticed 'distinctly grey' wisps of clouds and virga like projections.At level; it appeared as grey smog. We confirmed a slow and steady (but slight about 30-40 degrees Celsius) EGT rise on both engines. Re-examining our situation; we concluded a climb and an offset south would clear us from the grey haze and wispy clouds. The wind was about 140 kts. There was nothing of note depicted on the weather radar. We climbed to 350 and offset 4 NM right of course and could visually see that we were clear of the greyish layers below us. We both confirmed that the EGTs (Exhaust Gas Temperature) were normal. All engine indications were normal. We continued for another 10 minutes; monitoring indications. We pressed the EICAS event marker. The weather below us continued to clear; with now only small cumulus clouds low to the surface below us. We did continue to see the grey haze layer below us also. That is when the weather radar picked up strong returns below us; and we documented the event with the pictures provided. We contacted [Dispatch] with our status and location and asked Dispatch to report to ATC. As we passed over the radar returns; they cleared with no further indications. The grey haze also dissipated as we continued east. The Captain was informed and coordinated with [Dispatch] and ATC for a precautionary divert into ZZZ. Possible flight into area of [unforeseen] volcanic ash cloud.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.