Which line from “The Leap” foreshadows what happens during the storm?
There are, in fact, a number of lines that foreshadow the lightning, storm, and fire that claim Harry Avalon's life and forever change Anna's. In the second paragraph, the narrator talks about her mother's former life:
I would, in fact, tend to think that all memory of double somersaults and heart-stopping catches had left her arms and legs were it not for the fact that sometimes, as I sit sewing in the room of the rebuilt house in which I slept as a child, I hear the crackle, catch a whiff of smoke from the stove downstairs and suddenly the room goes dark, the stitches burn beneath my fingers, and I am sewing with a needle of hot silver, a thread of fire.
The reader discovers that the narrator should have no memory of the event because she was not born at that time, so her recall must come from the newspaper stories she has read about the event; her mother does not talk about it.
The narrator also talks about what causes the fire in her description of the storm to come in paragraph 4. The irony of the day is detailed by how refreshing the weather feels to the circus-goers, though the narrator describes how when hot and cold hit, strong storms form. But, of course, no one expects that.
In the third paragraph of "The Leap" by Louise Eldrich, the narrator declares that she owes her life to her mother three times, the first of which occurred when her mother was a trapeze artist, part of the duo that called themselves The Flying Avalons. She mentions, too, the replica of the tent pole that stands in the town square because
[I]t commemorates the disaster that put our town smack on the front page of the Boston and New York tabloids.
From this sentence the reader is able to infer that something occurred--a "disaster" under the circus tent. And, from the first sentence of the paragraph, the reader can also infer that as part of the Flying Avalons, her mother, to whom she owes her life, must have somehow been involved in this disaster before the narrator was born.