The general Quenya word for “snow” derived from the root √(G)LOS (PE17/26; VT42/18), more specifically “fallen snow” (RGEO/61), as opposed to a “snow fall” or “✱falling snow” which is hrissë (PE17/168). At various points Tolkien said this word could also be used as an adjective “snowy, snow-white” (RGEO/61; PE17/161), but I would do so only in poetry or in compounds. For more ordinary speech, I would use the adjective form lossëa for clarity (PE17/71, 161; VT42/18). Strictly speaking, the noun and adjective forms of lossë have distinct primitive origins: ✶lossē “snow” vs. ✶lossĭ “snowy, snow-white” (PE17/161), so the stem form of the adjective would be lossi-.
Conceptual Development: In The Etymologies of the 1930s there was a word ᴹQ. olosse “snow, fallen snow” derived from the root ᴹ√GOLOS; Tolkien modified the entry to mark this form as poetic (†) and gave it a variant olos (Ety/GOLÓS).
lossë (2) noun "blossom" ("usually, owing to association with olosse snow, only used of white blossom") (LOT(H) )