it's a great weather

Is it correct to use the article in It's a great weather.

Or one must not use the article and It's great weather is correct?

It's great weather.
It's a great day.

Thanks for a great answer.:p

Weather is a non-count noun (it can't exist in the plural). Thus you can never say 'a weather', only 'the weather'.

The weather is great.
It's great weather.

Both are correct. :-D

"Weather" > Это слово - одно из неисчисляемых существительных. С неисчисляемыми существительными неопределенные артикли a и an не употребляются.

Сказать по-английски было бы по-русски как "Сегодня хорошие погоды у нас."