Snow on the Hallelujah Mountains?

[Patrice Maire]

Okay, time for the plant person to step in.
IT's been established that the area where the movie takes place is the equivalent of a tropical jungle. What we saw in other areas (the plains and the coast) the plant diversity is very wide.
The plants on top of the floating mountains is different than the plants growing on the planet itself. There are likely micro climates on each individual floating rock as well and due to their floating and rotating, the climate changes constantly as well.
The flora at Site 26 seems to bear out a different weather pattern than on the ground. Long grass, different plant varieties that seem to indicate possible colder weather tolerance.
So, we'll have to see what Cameron plans for us in the next movie and perhaps in the novel as well.