I don't know how one would distinguish between a wonderful day and a glorious day. But a sunny day can also be a very windy day. When the mistral is blowing in the Rhone valley that can be given as grounds for committing murder.
The expression can be used either literally (when it would probably be a sunny day, although other conditions might influence, like Thomas Tompion has said) or figuratively, because someone is feeling great.
I would say that the most probable match is "wonderful day" but it does depend on the context somewhat.