I agree with Mary about this one: "What nice weather!" sounds old-fashioned to me. Nevertheless it is used some. In my part of the USA, Indiana, it's common to hear simply: "It's nice today." or "Sure is nice today." We generally omit the word weather. These would be casual verbal statements. With all due respect to Amanda, "What a nice weather" is not correct.

Ok, you have to decide if you are asking a question or making a statement. Question: Is it nice weather today? Answer: Yes, it is nice weather today. Statement: What nice weather it is today. or just "What nice weather" Try to avoid the rising inflection question in writing especially as the rising inflection means different things iin different cultures. In British culture it just means you are uncertain and a little confused, in some other cultures it means a question, but since you cannot see the inflection in the sentence it is not there. "?!" does not mean anything. "?" means a question, "!" means the comment is showing surprise, so you might use if after many bad days of weather, for instance.

"The weather's so nice today!" is what we usually say. "Nice weather today!" is also OK if you are talking or casually writing. "What nice weather!" sounds old-fashioned to me. "It's nice weather today!" is incorrect where I come from. Hope this helps :)

Yes, you can say 'It's nice weather today'. This is a statement. You can also say 'What nice weather!'. This is an exclamation. You could say either of them in a similar situation, but linguistically they are different. Mary may have a point that about regional differences, though. Both expressions are fine in UK usage, but they may be less common in the USA. It would be interesting to see what other members think.

Is the weather nice today? or Is it (it meaning weather) nice today? What a nice weather means "Wow today the weather is really nice.!"