Hi again Christina,
Planting the tree outdoors is not what I meant. What people do is bury the pot as well as the tree just for fall and winter. (I personally don't do this msyelf but, it is one method)
Bonsai means: Potted Tree so if you plant the tree outside, it will no longer be a bonsai.
Okay, as far as moving the tree outside. Just putting it outside now would shock your tree and that would not be good. I would suggest moving it to your garage (provided that you have some windows) or to some other somewhat sheltered area first. Leave it there until christmas and water accordingly.
Get your dad to leave the tree in a sheltered area for a few more weeks to acclimatize the tree to the lower temperatures.
Then, (my number one suggestion would be to) place the tree and pot in a much larger pot with some straw, newspaper or some other insulating medium.
Check out the Helpful Gardener's advice on bonsai trees on the website. I'm sure that he'll be giving some more advice shortly.
Also, once spring comes round get your dad to fertilize the tree with some liquid seaweed fertilizer diluted as per the instructions on the container. I get my liquid seaweed from a local nursery for about 8 dollars a bottle but, you can also get it at big box stores (though I would personally prefer that you bought it at a local nursery