Mr. Avery, a misopedist, contends that it has snowed in southern Alabama, where such an occurrence would be extremely rare, because of children who disobey their parents and commit other bad behaviors such as smoking cigarettes.
"See what you've done?" he said. "Hasn't snowed in Maycomb since Appomattox [the town Virginia where Lee surrendered to the Union, ending the Civil War]. It's bad children like you makes the seasons change."
Judging from his own crude behavior from the porch one evening of the previous summer and his solitary life, Mr. Avery seems to live a rather disgruntled life, and perhaps wishes to make others equally miserable. At any rate, he inflicts a gratuitous insult upon the Finch children. It is curious that the snowman that they erect bears a surprising resemblance to Mr. Avery, whose round belly and wooden eyes and mouth look "cross" as he often does.
When Atticus sees this snowman, he admires Jem's creativity. Then he laughs as he scolds Jem, "You can't go around making caricatures of the neighbors."
Mr. Avery's comments about the snowfall are used as just one way to demonstrate the belief structure and the superstitions in the Maycomb community. As is true of all human nature, the members of Maycomb seek for explanations to the events that occur around them. Avery says that the snow is a consequence of the bad behavior of children. When children disobey their parents and act badly, he says, then they cause the seasons to change. Besides the superstition, this comment shows that Avery is prejudice against children, just as so many in the town are prejudice against African-Americans.
Mr. Avery probably does not truly believe this, but his claim in Chapter 7 is that disobedient children are the cause of odd weather phemonena. Here is the quote:
Mr. Avery said it was written on the Rosetta Stone that when children disobeyed their parents, smoked cigarettes and made war on each other, the seasons would change: Jem and I were burdened with the guilt of contributing to the aberrations of nature, thereby causing unhappiness to our neighbors and discomfort to ourselves.
Avery's intimidation adds to the list of lies adults tell and serves to further distance Jem and Scout's upstanding, moral, truthful father as unique among the inhabitants of Maycomb.