That's a really difficult a question. In British English either is equally correct though they can have subtle differenced in meaning which I am finding difficulty explaining. Of course you have the third variant which is "Covered 'in' snow".
I'm sure that somebody else can describe it in technical terms. But my understanding as a natural English speaker is....
Covered 'by' snow kind of infers that this action has recently occurred.
e.g. The parked car was covered by snow.
Covered 'with' snow kind of infers that the object has not recently been covered.
e.g. The parked car was covered with snow.
Covered 'in' snow is kind of descriptive.
e.g. The parked car was covered in snow.
You know what I don't think it matters, choose one and use it,
An avalanche is like a rockslide, but on a snow-covered mountain.
It means that the street is completely covered by a solid sheet (or metaphorical blanket) or snow. Someone looking at it would only see snow, and not the street.
Yes
parts of the ocean were frozen and covered with snow.
It Is A Tundra.
The word fell is superfluous in that sentence. I would say, the snow covered the fields like a blanket.
In usual text, snow-covered would probably be hyphenated - otherwise the sentence could be misinterpreted - consider the difference between the concept of "snow-covered mountains" and the sentence "snow covered mountains".
Because it's covered by a snow cap
An avalanche is like a rockslide, but on a snow-covered mountain.
Because it's covered by a snow cap
Pure As the Blood Covered Snow was created in 2003.
steep snow-covered hill, and a trigger
Snow-clad; snow-covered.
Yes
well ,rivers with no snow
Only high in the mountains and on glaciers does it remain snow covered.
An avalanche is like a rockslide, but on a snow-covered mountain.