Most likely the President of Iran's helicopter had an encounter with a Granulocumulus cloud.
AP: Iran’s president killed in helicopter crash, election set for next month
Granulocumulus as in mountain hiding in the clouds (Granite+Cumulus).
It's likely this occurrence is what is known as a CFIT, or controlled flight into terrain event. This is where the operator of the craft which is otherwise working fine flies it into the ground. As the helicopter was flying in a mountainous area low visibility in fog, that is the pretty typical scenario for such. Combine it with potential maintenance issues on top of pilot disorientation, and this stuff happens.
On the upside, the "Butcher of Tehran" along with the other members of the Iranian regime onboard the helicopter are those whose deaths should not be mourned by decent folks. Considering they happily killed thousands of their own people, and orchestrated terror campaigns elsewhere including against the USA, the world is far better off without them.








