Skyrim contains many holds that each have a different climate.
Falkreath is mainly a large forest, with a large lake in the middle. Towards the southern end of Falkreath, at the border to Cyrodiil, it is very snowy and mountainous.
Hjaalmarch is predominately a swampy hold, with snowy, mountainous landscapes to the southern and eastern borders. While in the hold, especially at night, there is a very noticeable, thick fog that can limit any adventurers sight so that any potential threat can get closer without being spotted.
The Reach is a very rocky, mountainous hold which has rivers cutting through it here and there. Due to the mountainous nature and many rivers, a large quantity of waterfalls are present throughout the hold.