It's just that many words can have two variants of plural, for ветер they are ве́тры and ветра́. Those that end in и and ы are usually normative, the others that end in a stressed а or я are somewhat spoken, sometimes dialectal. Again, you can say it both ways: сильные ветры sounds okay and is the preferable form in neutral style, but сильные ветра́ is just as fine and may sound more poetic or colloquial.
See this helpful site - it indicates that, "The dictionary form of a Russian adjective is normally the normal, nominative, masculine form. These will almost always end in the letters '-ый' or '-ий.'" (There are short-form adjectives, but I haven't gotten to them yet.) (Also - adjectives ending in ый and ий decline with the gender of the noun.)