Cooler outside temps = lower overall tire pressure
This time of the year it's often a factor of fall climate change. Mine has gone off this time of year before, signaling that I just need to add a little air to each. Usually the TPI light goes off in a matter of moments. If that doesn't do, better have your local service station check for nails, etc.
FWIW, I was in Montana three summers ago during a very hot spell, and I got in the vehicle early one morning after a cool overnight rain. The light went on and that's all it was...cooler temps made the pressure decrease and the I just added air and was happily on my way.
-Karen in AZ-