Implicating overcast → sky
Link to implication

Reason:

If you can't see the sky, how could you tell that it's overcast?

Also:
overcast -> clouds?

Genjar said:
overcast -> clouds?

post #815871 I'd say this definitely deserves "overcast," but there's no actual cloud (By the way, Clouds was aliased to Cloud. We need a preview submission for the implication/alias submissions for this) visible in it, just a gloomy grey sky.

What about overcast -> sky?

Hudson said:
What about overcast -> sky?

I was about to argue that I thought of sky as blue_sky, but lo' and behold, there's a tag for that.

Overcast is grey clouds coming together but actually not raining.
So in other words, if the picture has grey/rain clouds as/in the background, then that would be where overcast tag would fit in.

Source: Google:

"(of the sky or weather) marked by a covering of gray clouds; dull"