This price is available for flights departing on Fridays, returning on Sundays, in late January and early February. You'll find even lower fares for mid-week travel, but we all know it's easier to get away for a quick weekend than it is to fly during the middle of the week.
I found seats departing Phoenix PHX on Friday, January 25, returning from Portland PDX on Sunday, January 27.
Since Southwest includes two free checked bags, you won't have to worry about any extra bag fees and you'll also be able to change your flights without paying an extra change fee should your plans change.
If you're looking for tips on how to spend a weekend in Portland, read our guide on The Best Weekend in Portland Ever.
Need a room in Portland? Here's what's available for the mentioned weekend dates on Hotelwatchdog.