Wash. Rev. Code § 35.58.112
The metropolitan council of a metropolitan municipal corporation upon the affirmative vote of two-thirds of the members of such council may make planning, engineering, legal, financial and feasibility studies preliminary to or incident to the preparation of a recommended comprehensive plan for any metropolitan function, and may prepare such a recommended comprehensive plan before the metropolitan municipal corporation has been authorized to perform such function. The studies and plan may cover territory within and without the metropolitan municipal corporation. A recommended comprehensive plan prepared pursuant to this section for any metropolitan function may not be adopted by the metropolitan council unless the metropolitan municipal corporation shall have been authorized to perform such function.
RCW 35.58.112