"How It Ends" never really has a beginning or an end. You have fragments, tiny bits, and pieces like when you empty a three-hole punch and miss the trash can. I can't gather up enough good bits to give a single star. But I must just to be able to post this review.
While waiting for the roles of the characters to come together you find that you have been on a road trip for more than half of the movie.
The eruption of the Yellowstone Caldera triggering the other events at least would give you a starting point and reference to anchor you in the chaos.