From what I've read, the nickname came from Chicago boastfulness, not its weather.
From the stltoday.com
Individualism and self-belief is not synonymous with boastfulness and superiority.
From the guardian.co.uk
The boastfulness of the advance is gone,-and there is chance for sober reflection.
From the theatlantic.com
His cooking confidence shouldn't be mistaken for boastfulness, however.
From the expressandstar.com
When an NBA player acts odd, it's usually an over-abundance of arrogance or boastfulness.
From the charlotteobserver.com
But some potential customers may find the firm's arrogance, even boastfulness, offputting.
From the economist.com
She speaks without a hint of boastfulness or bitterness, and some details must be coaxed from her.
From the cnn.com
Unfortunately, the Sun-Times confused that confidence for boastfulness in their recent editorial.
From the suntimes.com
McLain captures Hemingway's legendary charisma, and his fatal tendencies toward bullying and boastfulness.
From the guardian.co.uk
More examples
Outspoken conceit
(boastful) exhibiting self-importance; "big talk"
Boasting is the act of making an ostentatious speech. It is considered a vice by such major religious groups as Christianity, Islam, Hinduism, and Buddhism. Boasting has also been studied by such evolutionary psychologists as Robert Wright.