RCW 4.56.115: Interest on judgments against state, political subdivisions or municipal corporations—Torts.

Judgments founded on the tortious conduct of the state of Washington or of the political subdivisions, municipal corporations, and quasi municipal corporations of the state, whether acting in their governmental or proprietary capacities, shall bear interest from the date of entry at two percentage points above the equivalent coupon issue yield (as published by the board of governors of the federal reserve system) of the average bill rate for twenty-six week treasury bills as determined at the first bill market auction conducted during the calendar month immediately preceding the date of entry thereof. In any case where a court is directed on review to enter judgment on a verdict or in any case where a judgment entered on a verdict is wholly or partly affirmed on review, interest on the judgment or on that portion of the judgment affirmed shall date back to and shall accrue from the date the verdict was rendered.