In Kate Chopin's short story, Mrs. Mallard has just been informed of her husband's death. She retreats to her room, sits in her chair and gazes out the window. The scene is described as an "open square" where the "tops of trees were all aquiver with new life." "Patches of blue sky" were visible "through the clouds."
These sights parallel Mrs. Mallard's dawning feelings of freedom and possibility now that her husband is gone. She, too, feels aquiver with new life. What potential she sees for the future! In a few short paragraphs, she experiences the intense joy of freedom, then sees her hopes crushed when her husband returns home, alive and well, having missed the train that crashed fatally.
And she dies, of what her doctors conclude is the "joy that kills."
There is so much foreshadowing in the description of what Mrs. Mallard sees outside her window:
She could see in the open square before her house the tops of trees that were all aquiver with the new spring life. The delicious breath of rain was in the air. In the street below a peddler was crying his wares. The notes of a distant song which someone was singing reached her faintly, and countless sparrows were twittering in the eaves (para. 5).
There were patches of blue sky showing here and there through the clouds that had met and piled one above the other in the west facing her window (para. 6).
In addition to the foreshadowing explained in the other responses, there are the sounds of the sparrows Mrs. Mallard hears, birds that are free to fly, while she has been a bird in a cage in her marriage. The "open square" is a reference to the open life she believes she can now have, and the clearing of the sky symbolizes how the clouds in her own life, i.e., her marriage, are now cleared away, or so she believes. Mrs. Mallard sees how she can now sing in happiness, like the birds or like the distant singer she hears below. And she can also smell the rain, which symbolizes not only spring and new life, but also cleansing, a way of cleansing herself from what was clearly an unhappy marriage.
This is a wonderful use of foreshadowing, not only because of its careful choices of words that presage Mrs. Mallard's fleeting hope for freedom and new life, but also because of its vivid imagery. Chopin appeals to the reader's sense of sight, smell, and sound in these passages, providing a fuller image of new life and freedom than just visual imagery would have accomplished.
When Mrs. Mallard first learns of her husband's death, she is overshadowed with sorrow and grief. The patches of blue sky among the clouds foreshadow how her grief is "clearing up" and something beautiful (hope) will be left behind. Spring is a time of new life and new beginnings, and this foreshadows the new life Mrs. Mallard will have for a short time.