I think it's dangerous to climb a mountain on a stormy day.

Literal

Storm [possessive-の] day [time-に] mountain [to-に] climb [nominalizer-の] [topic-は] dangerous [quotative-と] think.

嵐の日に山に登る (to climb a mountain on a stormy day) sets the scenario. ~と思う (I think) frames it as the speaker's opinion. 危険 (dangerous) is the core judgment.