It is snowing heavily and he can see frost on the windowpane what type of water transition is that? ?

Hi there!
So you are looking for the phase transition of snow to ice!

Snow is microcrystalline hexagonal ice, which is the only phase of solid water that is stable at the temperatures and pressures near the earth's surface.
In what we know of as "ice" these crystals are simply larger.
So there is technically no phase transition from snow to ice!

However, by asking this question, your teacher probably wants to test if you understand the phase transitions. So you probably need to mention that in order to get from “snow” to “ice”, the snow has to melt and then refreeze.

The answer your teacher is probably looking for is this :

Melting of snow to water, and then freezing of water.

In other words :

H2O(s) → H2O(l) → H2O(s)

There you go! I really hope this helped, if there’s anything just let me know! ☻