We are going to climb the mountain. The weather is bad this weekend.

Unless the weather is bad this weekend, we will go climbing. IF means IF, if the result is positive, then the clauses guided by if (clauses are separated by commas before the main clause) use the simple present tense, and the main clause also uses the simple present tense. If the result is possible, the main sentence (clause uses the simple present tense) uses the simple future tense. UNLESS is equivalent to IF NOT, that is, IF NOT/ unless, which means the same usage as IF just now. Conclusion: The result is affirmative, that is, the Lord now (in time) comes from the present (in time), and the result is possible, that is, the Lord will come from the present. No matter whether the result is affirmative or possible, the clauses are simple present tense, but the main clause has changed! So choose d