Wash. Rev. Code § 35A.34.270
All appropriations in any current operating fund shall lapse at the end of each fiscal biennium. However, this shall not prevent payments in the following biennium upon uncompleted programs or improvements in progress or on orders subsequently filled or claims subsequently billed for the purchase of material, equipment, and supplies or for personal or contractual services not completed or furnished by the end of the fiscal biennium, all of which have been properly budgeted and contracted for prior to the close of such fiscal biennium, but furnished or completed in due course thereafter.
All appropriations in a special fund authorized by ordinance or by state law to be used only for the purpose or purposes therein specified, including any cumulative reserve funds lawfully established in specific or general terms for any municipal purpose or purposes, or a contingency fund as authorized by RCW 35A.34.250, shall not lapse, but shall be carried forward from biennium to biennium until fully expended or the purpose has been accomplished or abandoned, without necessity of reappropriation.
The accounts for budgetary control for each fiscal biennium shall be kept open for twenty days after the close of such fiscal biennium for the purpose of paying and recording claims for indebtedness incurred during such fiscal biennium; any claim presented after the twentieth day following the close of the fiscal biennium shall be paid from appropriations lawfully provided for the ensuing period, including those made available by provisions of this section, and shall be recorded in the accounts for the ensuing fiscal biennium.
RCW 35A.34.270