When a loved one dies accidentally, you develop tunnel vision. Your mind teems with questions: Was it quick? What were his final thoughts? What if his plans had been different that day? And when a loved one dies by suicide, that tunnel vision becomes a myopia the breadth of a laser that threatens to consume you. In “Strange Weather,” writer-director Katherine Dieckmann (“Diggers”) explores how people who kill themselves inevitably claim more than one life. It’s a hot and bone-dry September in Georgia when we meet Darcy (Holly Hunter, scrappy as ever), an administrative assistant who would rather spend her.