It looks as if it's going to rain

[mariethe house]

What is best:
It looks as if it is going to rain
or
It looks like it is going to rain

Is it a difference between British and American English?

 

[nickm70]

They are both fine with the second being more common here.

 

[Miss Julie]

And we'd be more likely to say

It looks like it's going to rain.

 

[Pertinax]

I would say that "like" is also more common in AuE. It would often be shortened informally to:

[It] looks like it's gonna rain.
[It] looks like rain [coming].

I would use your first form with "as if it's" or "as though it's" in a more formal setting.

 

[djmc]

To me, BE, both look normal; I would use either without really thinking about it. English, indeed any language, often has several ways of expressing anything in particular. Often there are are slight tinges of difference, but that doesn't seem to be the case here. The expressions are just different ways of saying the same thing. In dialogue one person might repeat what another has said but slightly differently.
A: It looks as if it's going to rain.
B: It looks like it doesn't it. I better get the washing in.

 

[Pertinax]

I think that there is a reluctance to use "like" as a conjunction in formal BrE, though as a preposition it's fine.

 

[peptidoglycan]

It looks as if it is going to rain: Formal speech

It looks like it is going to rain: Informal, everday speech

 

[djmc]

I disagree here. Neither are particularly formal or informal. They are just variants.

 

[Codinome Shlomo]

I would say that "like" is also more common in AuE. It would often be shortened informally to:

[It] looks like it's gonna rain.
[It] looks like rain [coming].

I would use your first form with "as if it's" or "as though it's" in a more formal setting.

So it is possible to say, "it looks as though it's going to rain"?

 

[Einstein]

I think that there is a reluctance to use "like" as a conjunction in formal BrE, though as a preposition it's fine.

Yes, this was certainly true 30-40 years ago and I remember teaching that "like" is only a preposition. To say "he looked like he'd seen a ghost" was quite non-standard in BrE and to me sounded particularly AmE. But times have changed and I notice that "like" is used this way by a lot of BrE speakers nowadays.
Iìd say that in formal writing "as if" is still preferred; I believe Americans prefer "as though", which is fine in BrE too.

 

[Thomas Tompion]

The ngrams are interesting and, I think, informative here.

Being a boring old fart, I couldn't say It looks like it is, though it doesn't make me feel actually bilious. I would have to say It looks as though (or as if) it is.

The ngrams only use the written word, so that may prejudice against the newfangled.

I was pleased to note that BE people still seem reluctant to write It looks like it is.

 

[sound shift]

Yes, I feel a bit reluctant to say "It looks like it's going to rain", but I'm not sure I did before I saw the matter discussed elsewhere in the WR forum.