Go to Yahoo, not Yahoo Answers by clicking on the Yahoo in the top left of this page. Now click on your name where it says Hi, Jim (or whatever your name is). That should bring you to the Account information page. Scroll down to where it says Address/Contact Information and click on edit. This will allow you to change your zip code. If you change your zip code to 49085 and click finished and then finished again you should get weather for St Joseph.
Actually I am full of it. You also have to put your curser of the weather. A change location should come up. Enter 49085 there and it should work.