That looks really good! I just have a few improvements, nothing big.
Wind.interplorateWindSpeed()
A math function called signum could be used instead of ifsif statements.
float speedDiff = targetSpeed - speed;
float speedChange = (float) (sqrt(abs(speedDiff))/15);
speed += speedChange * signum(speedDiff);
Wind
You might consider moving all the private floatsfloats values into a constructor, just for consistency.
Thoughts
Really these are just small tweaks, you have some very well-written and documented code!
The next thing to do would be to make more types of snowflakes (hexagons, stars, textures) for variety.