This is looking like it'll be a similar type of weather event to the one that caused all the flooding in Northern California last week. Looks like they're starting to mention flooding concerns in Portland. The one thing PDX does have going for it is there's not a lot of traffic there (relatively speaking). It's rare to see a delay posted there due to traffic backups, so any delay would more likely be due to the weather itself.
You might start looking at SEA as the weather there is supposed to be a little better (but still wet). I probably wouldn't change anything yet, but I'd start looking at my options.