Are Familiars affected by weather conditions?

Question

Since a familiar is a magical spirit (celestial/fey/fiend, albeit in a physical form), does it have any restrictions to travel in cold/hot areas for scouting purposes, or altitude of mountain air?

I'm trying to use my owl familiar to scout mountains, and my DM tells me that it's too cold and/or high for him to be able to scout. Would I have to recast and change the species of the owl to snowy, or would being a celestial owl prevent having to do this? Obviously if its too hot they burn and die, and if it gets too cold they freeze, but as a magical spirit that can travel between dimensions, where should the line be drawn?

The 3e/3.5e template is way overpowered (spell resistance, etc), but this feels almost entirely too weak. How limited is a familiar by their physical form if they're no longer considered a "beast?"

Answer 1

A familiar is affected in the same way a typical creature of that kind would be.

From the spell description of find familiar:

Appearing in an unoccupied space within range, the familiar has the statistics of the chosen form, though it is a celestial, fey, or fiend (your choice) instead of a beast.

The only difference between a familiar and a typical beast is its creature type, and the abilities explained further in the spell description. Creature type confers no innate benefits, but only changes how the familiar relates to features the concern creature type.

Therefore, it is entirely up to the DM to rule how a particular animal would be affected by the current environmental conditions, and the same goes for your familiar.

Note, find familiar let's you summon your familiar as an owl, not a snowy owl (there is no statblock for a snowy owl). Find familiar is restricted to the printed creature types and their respective statblocks as they appear in the Monster Manual or Player's Handbook.