For durative verbs this is quite easy for me to grasp:
鳩が見る: I will see a dove
鳩が見ている: I am seeing a dove
鳩が見た: I saw a dove
鳩が見ていた: I had been seeing a dove
But for perfective verbs — it is quite hard for me:
杪冬の前に雪が溶ける: Before the end of winter the snow will melt
杪冬の前に雪が溶けている: Before the end of winter the snow will already be molten
杪冬の前に雪が溶けた: Before the end of winter the snow melted
杪冬の前に雪が溶けていた: Before the end of winter the snow had already been molten
In both of the last cases before winter began the snow is already in a state of being molten as a result of the melting being complete. So I often make mistakes differentiating the last two cases and treating them as the same even though I consciously know the ～た emphasizes the action being completed and the ～ていた emphasizes the state change being already completed. Maybe someone can help?
Not a native speaker, but nobody else has jumped in, so here’s my understanding of it. Take it with a grain of salt because I’m not a native speaker. If you want I could ask my sensei for clarifications, I just would prefer to not bother her.
These two phrases only have a different nuance, not technically a different meaning. The nuance is exactly what you described in what you consciously know. So you might use the 〜ていた form to say how it was safe for you to go on a hike, and the 〜た form to focus on the season change itself. It’s not necessarily wrong to use them interchangeably.