If you were divorced in Mississippi, the Court still hs jurisdiction over these issues. You do not say how long it has been since the move but look at your divorce judgment and there should be a provision in it that requires each party to report any change of address to you and the Court, see if she has filed her new addres with the Court. There may be issues with the Uniform Child Custody Jurisdiction And Enforcement Act ("UCCJEA"). You can read about it at a variety of places online but you should seek the advice of counsel, locally first and they will let you know if you need a lawyer in Washington State.
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