Asynchronous Loop of jQuery Deferreds (promises)

I am trying to create what I think is referred to as a "Waterfall". I want to sequentially process an array of async functions (jQuery promises).

Here's a contrived example:

function doTask(taskNum){
    var dfd = $.Deferred(), 
        time = Math.floor(Math.random()*3000);

    setTimeout(function(){
        console.log(taskNum);
        dfd.resolve();
    },time)

    return dfd.promise();
}

var tasks = [1,2,3];

for (var i = 0; i < tasks.length; i++){
    doTask(tasks[i]);
}

console.log("all done");

I would like it to complete the task in the order they are executed (present in the array). So, in this example I want it to do task 1 and wait for it to resolve then do task 2 wait for it to resolve, do task 3 etc and the log "all done".

Maybe this is really obvious but I've been trying to figure this out all afternoon.