IR sensors can be used to see through smoke. I don't know about UV but could birds' IR vision (if they have it) enable them to see through at least thin cloud?
Some birds like swifts seem to spend quite a lot of time in the air with wings folded, between short but fast bursts of flapping. I suppose this is an advantage all birds have - they can at will dump all lift. As long as they have sufficient semi-circular canal apparatus to sense gravitational acceleration downwards then all they have to do know which way is down in IMC is stop flying, sense in which way they accelerate i.e. downwards and take whatever action is necessary to stop it.