Today may be all warm and in the 40s, but tomorrow.... tomorrow meteorologists are already describing as a frighteningly vague "major event."
Snow! beginning in the afternoon.
Freezing Rain! continuing until midnight.
"Significant amounts of snow, freezing rain, ice, or slush!" destroying your commute.
If you have to drive up hills, use chains. If you can, take transit and pray to the Gods of TriMet that your bus doesn't get stuck.
Best case scenario: Stay home and film people out your window.