In Italian, nevi (the plural of neve, "snow") is used in some expressions, such as l'uomo delle nevi (a.k.a. Yeti), and le nevi dei Pirenei. (The last expression is referring to the Pyrenees, but I could use it when referring to any mountain belt.)
Is snows ever used as noun (even if in set phrases), or is it never used as noun?
'Snow' is what is called a 'mass noun'. Like 'water' or 'traffic', it already describes a collection of things (a mass) and so there isn't likely a number of such items, just some of it.
'The snow that fell overnight was deep' is correct.
'The snows that fell overnight were deep' is incorrect (or poetic)
You can however talk about multiple instances of water, 'the glasses of water' which can be said grammatically as 'the waters in those glasses' but that is a strange transformation, almost poetic, and surely to be avoided in speech and most writing.
'The snows that fell in each of the towns were deep.'
works and occurs, but is a somewhat strange way to say it. One would more likely reword it to avoid the strange plural.
'The snow that fell in each of the towns was deep.'
or to emphasize that a snowfall occurred in a number of towns, and though the depth was different in each one, the amounts were all deep.
'The different amounts of snow in the towns were all deep.'
sounds much better. So the answer is yes, 'snows' can be used as a plural noun but it is not common and is not natural sounding. So if you are translating from a language with plural snow, you should reword to avoid the plural.
For a comparison here is the google nGram comparing 'the snow' and 'the snows':
Yes, "snows" can be used just like this in English. A classic of English literature is Hemingway's story "The Snows of Kilimanjaro".
Yes, snows may be used as a noun.
However, when it is, it is not simply the plural of snow. Snow is itself a "mass noun", meaning a singular form that refers to a large collection of small things. The plural refers to episodes or events involving snow. In other words, snows refers to several instances of "snow falls".
The heavy snows on the north side of the mountain frequently cause avalanches.
A similar case is a word like sand, where the singular noun for actually refers to a large collection of grains of sand, but you could refer to "the barren sands of Africa" and people will understand various different deserts full of sand rather than just one.
Yes, it is an English word. It is occasionally used in the way that Mark Beadles described. However it is usually used in sentences such as, "It usually snows between November and March."
See Google Ngram Viewer: snows, it snows, the snows, of snows:
Most translations of François Villon’s poem, “Ballade des dames du temps jadis”, use snows in the refrain, where “Mais où sont les neiges d’antan” becomes “But where are the snows of yesteryear?”
"Snows" would be plural, and therefore a noun, when referring to INSTANCES of "snowing."
Such "instances" may take place on separate days, "the SNOWS of Monday, Tuesday, and Wednesday," or in different places, the SNOWS of New York City, Boston, and Philadelphia."
