Here is some language from the site Washingtongunrights.com:
FACTS ABOUT CARRYING A FIREARM IN WASHINGTON STATE
(1). Washington is an "open carry" state for firearms. This means a person may carry a firearm in an exposed holster without any kind of permit unless there is something that makes it specifically illegal. (For example, carrying a weapon onto primary or secondary school grounds or other prohibited places, or carrying a weapon by most felons or anyone convicted of a domestic violence crime.) (2). Unlawful carrying (RCW 9.41.270) occurs when the person carries or displays a weapon “in a manner, under circumstances, and at a time and place that either manifests an intent to intimidate another or that warrants alarm for the safety of other persons.” This is something more than just walking around with an exposed firearm.
(3). Unlawful carrying without a Concealed Pistol License (CPL) occurs when a person carries a concealed pistol on his person and does not have a CPL. A person may carry a loaded firearm in a vehicle only if they have a valid CPL. Those without a valid CPL may carry a firearm in a vehicle only if the firearm is unloaded and not concealed in any way on the body. (RCW 9.41.050) Exemptions exist in RCW 9.41.060
(4). Due to state preemption, no city, town, county, or other municipality can restrict your right to keep and bear arms more than the state. (RCW 9.41.290)
(5). Carrying concealed (with a CPL) or openly in establishments that serve alcohol is allowed in Washington, so long as it is not carried into an area designated as “no minors allowed” by the Washington Liquor Control Board. Refer to RCW 9.41.300 to view the complete list of prohibited places.
(6). Washington fish and wildlife laws prohibit the transportation or possession of a loaded shotgun or rifle in a motor vehicle by any person, regardless of CPL status. Detachable magazines may remain loaded if they are not attached to the firearm. (RCW 77.15.460)
(7). There is NO stipulation that a Washington CPL holder MUST carry concealed. Furthermore, lawful open carry of a firearm is NOT grounds for revocation of a Washington CPL.
8. Washington is a “shall issue” state. This means that the issuing agency must issue a Concealed Pistol License (CPL) to any applicant that meets all statutory qualifications – Resident & Non-Resident. If you live in the unincorporated area of a county you must apply in person at your sheriff’s office. If you live in an incorporated city within the county, you may apply in person at either the city police department or sheriff’s office. If you are not a Washington State resident you may apply at any local law enforcement agency in the state. (RCW 9.41.070)
Check out that site there is additional info in the faq's further down on the page.