The best option would be "Está a nevar muito", because the adverb muito alters the meaning of the verb nevar and if you take it to a position before the preposition it would seem like their relation was weakened. Anyway, that construction is only used on European Portuguese. In Brazil people would say "Está nevando muito". Hope I was of some help. bye bye

Portuguese (brazilian) é "Está nevando muito"

Está a nevar (Portugal) Está nevando muito (Brasil)

In this case we usually use present continuous. If you want to say "It's snowing a lot", the translation would be "Está nevando muito".

No Brazil, as pessoas usariam "Está nevando muito?" "a nevar" é uma forma mais usada em Portugal.