A low cloud at ground level that makes it hard to see
Encoding Strategies:
linguistic
visual

nebula
foggy cloud in space
Niebla means fog and is related to the English word nebula0, which is a giant cloud of fog floating in space.
niebla
fog, mist
A cloud that forms at ground level and blocks your view.
No pude ver la carretera por la nieblaI couldn't see the road because of the fog
Una niebla ligera cubría el valle por la mañanaA light mist covered the valley in the morning
fog, haze (mental)
Just like in English, a fog can settle over your mind or memory and cloud it.
Después de la mala noticia, pasé toda la semana en una nieblaAfter the bad news, I spent the whole week in a fog
Recuerda esos años a través de una niebla de dudasHe remembers those years through a haze of doubt