@Huxley,
Huxley, the following is not meant as a particular criticism of your post:
There is a breathtaking ignorance of the range of meanings for the words "grammar" and "language" being shown by respondents to this relatively technical thread.
Taking "transformational grammar" for example, the sentence
"The dog is brown" could be interpreted as one "surface" realization of the deep structure "the dog is a brown object". Another surface realization of that deep structure might be the phrase "the brown dog".
But that is merely one angle on the above arguments. We could also explore the field of comparative linguists where the English verb
to be maps to different verbs in Spanish (aproximately)
ser to be in a particular state, and estar to be actively doing something. It follows that the two OP sentences about "weather" could be associated with these different verbs.
The third point I would make, and for me the most significant one is that as soon as we engage in contrastive analysis we are taking utterances out of their original context. In other words "grammatical analysis" is an artificial academic pursuit rather than a "natural one". As Chomsky pointed out. children pick up " the grammar of their native language" without active intstruction, and even the latter tends to be about
exceptions to rules.
There is even an argument (by Wexler) that it is impossible to
adequately teach a second language to a foreigner without "cultural immersion"...but then of course the argument moves to one about "communicative adequacy",