When i fly around my world i once in a while find trees on chunkborders
where only half of a tree is covered with snow.The other part (in the other chunk) is without snow.
It only happens on generation of new chunks, if you change the weather to rain or thunder,
the rest eventually will be covered.
Seed is 1660602706 (big biomes selected ),two such trees can be found at [-250 ~ -330]