To discuss the weather with a stranger is to shake hands and put aside your weapons. It is a sign of good will, an acknowledgement of your common humanity with the person you are talking to.
This is from Gotham Handbook, an instructional piece set by Paul Auster for Sophie Calle. As part of a mission to make lovely conversation with strangers, Auster suggested talking about the weather and justified it so.
This quote chimed, not just because we're in Groundhog Snow Day.
Seen in the most excellent Calle exhibition currently at the Whitechapel Gallery.