What is an example of foreshadowing in Chapter 12-13 in To Kill a Mockingbird?

Some examples of foreshadowing include Dill's letter, Calpurnia's church's reaction to Scout and Jem, and Alexandra's arrival.

Foreshadowing is a hint that the author makes about something that is going to happen later in the book.  It keeps a reader guessing and interested in the story.  Lee uses foreshadowing many times throughout the book.

One example of foreshadowing is the description of Jem’s moodiness. Scout is annoyed by it, but she is told that Jem...

Some examples of foreshadowing include Dill's letter, Calpurnia's church's reaction to Scout and Jem, and Alexandra's arrival.

Foreshadowing is a hint that the author makes about something that is going to happen later in the book.  It keeps a reader guessing and interested in the story.  Lee uses foreshadowing many times throughout the book.

One example of foreshadowing is the description of Jem’s moodiness. Scout is annoyed by it, but she is told that Jem is just growing up.  This foreshadows the events of the trial, because it is a major time of maturing for Jem.

Another example of foreshadowing is the comments Dill makes about his father.  

But summer came and Dill was not there. I received a letter and a snapshot from him. The letter said he had a new father whose picture was enclosed, and he would have to stay in Meridian because they planned to build a fishing boat. (Ch. 12)

This incident foreshadows Dill’s arrival in Maycomb later in the book.  Dill writes that he is going to have a good time with his new father.  When his stepfather shows no interest in him, Dill runs away back to Maycomb to be with Scout and Jem.

Another example of foreshadowing is the reception Scout and Jem get when they got to Calpurnia’s church.  Although Lula is rude to them, most people treat them with respect.

When they saw Jem and me with Calpurnia, the men stepped back and took off their hats; the women crossed their arms at their waists, weekday gestures of respectful attention. They parted and made a small pathway to the church door for us. (Ch. 12)

This foreshadows the trial, especially when Reverend Sykes tells the children to stand because their father is passing.  Most of the African Americans in Maycomb respect Atticus and appreciate what he is trying to do in defending Tom Robinson.  The details of the trial are also mentioned during this visit.

When Alexandra appears, the conversation between Atticus and the children foreshadows the trouble with will occur in Maycomb before and during the trial.

“We felt it was time you children needed—well, it’s like this, Scout,” Atticus said. “Your aunt’s doing me a favor as well as you all. I can’t stay here all day with you, and the summer’s going to be a hot one.” (Ch. 13)

When Atticus says the summer will be hot, he is speaking metaphorically.   Maycomb is stirred up by the trial, and Atticus knows that things are only going to get worse.  He wants Alexandra there to look out for his kids, and as an extra system of support.