Headscratchers / Dragons: The Nine Realms

• The Riders are just fine walking around the Ice Realm in their normal cloths. But suddendly, in the final episode of season 5, they are freezing their butts off during a blizzard. Aside form the obivious out-of-universe explanations (the animators forgot/didn't care/didn't have the budget for models with winter cloths), does anyone have an in-universe explanation for this glaring inconsistency?
• How did Thunder know about the symbol of the original Dragon Club? Do dragons have oral history?
• How exactly asteroid "grazing" Earth could create such enormous fissure? To do something like that, the body in question should have enormous mass packed into tiny volume. Essentially somebody from outer space fired a solid neutronium projectile at the Earth - and barely missed.