Make AJAX "get" function synchronous / how to get the result?

I'm experiencing a problem of $.get function. The url contains JSON

my code:

 xyz = null

    $.get('http://www.someurl.com/123=json', function(data) {
       var xyz = data.positions[0].latitude;
    });

alert(xyz);
//some more code using xyz variable

I know that xyz will alert a null result because the $.get is asynchronous.

So is there any way I can use the xyz outside this get function?