Question

Why is Siberia much colder than western Russia?

Answer 1

Western Russia is part of the European climate zones, and tends to get warm
winds from the Mediterranean and Africa during the summers. Siberia is separated
from Europe by the Ural Mountains, and separated from the hotter parts of Asia
by the Himalaya (and connected) mountains, so it always tends to be a little bit
cooler than the European part of the nation (on average).

Answer 2

Siberia is much colder than actually most of Russia because it's much further up north towords the arctic