There will be unmarked spoilers from American Gods here.
Pretty much the first job Mr. Wednesday and Shadow pull together is the ATM job; before it, Wednesday asks Shadow to cause a snowfall - by thinking about snow. Shadow does so, and it does indeed snow.
The major thing about gods in the novel is that they're powered by belief, specifically by belief of ordinary people (which is actually a recurring theme throughout Gaiman's other works) - when I read that episode I thought this was the case.
However, later in the novel we learn that Shadow is not a mere man, but a son of a god.
Does that mean Shadow was able to cause the snowfall, do the coin trick (putting the golden coin in place of Sun in Iceland), and influence minds (like with Chad and Sam), only because of his heritage, and not because anyone can focus their belief to shape reality?