Wash. Rev. Code § 4.56.150
In all cases tried in the superior court with a jury, the defendant, at the close of the plaintiff's evidence, or either party, at the close of all the evidence, may challenge the legal sufficiency of the evidence to warrant a verdict in favor of the adverse party, and if the court shall decide as a matter of law the evidence does not warrant a verdict, it shall thereupon discharge the jury from further consideration of the case and enter a judgment in accordance with its decision, which judgment if it be in favor of the defendant shall be a bar to another action by the plaintiff for the same cause: PROVIDED, That in case the defendant challenge the legal sufficiency of the evidence at the close of plaintiff's case, and the court shall decide that it is insufficient merely for failure of proof of some material fact, or facts, and that there is reasonable ground to believe that such proof can be supplied in a subsequent action, the court may discharge the jury and enter a judgment of nonsuit as provided in RCW 4.56.120: AND PROVIDED, FURTHER, That nothing in this section shall be construed to authorize the court to discharge the jury and determine disputed questions of fact.
RCW 4.56.150
Rules of court: Cf. CR 50(a).