For weekend travel in February, fly nonstop from Seattle to San Francisco for $117 roundtrip on Alaska or Delta. If you're in the Bay Area and want to see the Pacific Northwest for a weekend, this fare also works from San Francisco to Seattle.
I found seats departing Seattle SEA on Friday, February 8, returning from San Francisco SFO on Monday, February 11.
You'll find slightly higher $133 roundtrip fares available for weekend travel throughout the year.
Need a room in San Fran? Here's what's available for the mentioned weekend dates on Hotelwatchdog.