Well, a snowstorm dominates the present-day timeline, and cedars and cedar wood are all over the place as well. As we've already mentioned elsewhere (see "Symbols"), snow and cedars are both pretty important symbolically. Snow seems to be associated with the unpredictable nature of life and its freak occurrences that place the human race at their mercy—you know, kind of like what war and love do to the characters.
Meanwhile, cedars have a happier meaning, associated with Ishmael's swoony memories of Hatsue and the limited sexy times he got to have with her. As we know, life's unpredictable ways end up "falling" hard on these happy times between Ishmael and Hatsue, so the title Snow Falling on Cedars seems pretty apt.