Setting selected value of a Select using JQuery from an MVC model property

I am am filling a dropdown using Ajax

$(document).ready(function() {

    var ID = $("#ID").val();

    fillDropdown(ID); //fills the dropdown via an $.ajax call

    var anotherID = @Model.AnotherID;

    //alert(anotherID);
    $("#AnotherID").val(anotherID); //try to set the selected value

});

The dropdown is defined in the page as:

@Html.DropDownListFor(x => x.AnotherID, Enumerable.Empty<SelectListItem>())

The line to set the selected value of the dropdown is: $("#AnotherID").val(anotherID);

and it only works if I uncomment the alert just above!

Any ideas why?