Hi Annie,
It is definitely not a black-legged tick (several Ixodes species) which are the only ticks that transmit Lyme disease, so no need to worry about that.

It looks like an adult male lone star tick (Amblyomma americanum). Here is a link to a photo of another one of these for comparison...
https://bugguide.net/node/view/773042

The only puzzling thing about this ID is that lone star ticks are not native to the Pacific Northwest. Did you or anyone close to you travel to the eastern US lately and perhaps bring back a hitchhiker?

Several pathogens can be transmitted by the lone star ticks and given the proper circumstances they may manifest into disease. These include ehrlichiosis, rickettsiosis, tularemia and protozoan infections. For more information, you can consult the publication here
http://entnemdept.ufl.edu/creatures/urban/medical/lone_star_tick.htm
 and/or talk with your doctor.

Bites of lone star ticks are also known to occasionally cause people to develop a delayed allergic reaction to galactose-alpha-1,3-galactose, which is present in mammalian meat and some medications. Here is where to find more information on this phenomenon…
https://www.cdc.gov/alpha-gal-syndrome/about/?CDC_AAref_Val=https://www.cdc.gov/ticks/alpha-gal/index.html
Hope that helps!