I assume Michigan can get pretty cold in the summer though? Find out what the temps can get down to and buy for that.

If the BA bag actually goes down to 15 degrees, I would be roasting in the Spring and Fall in Oregon. I have a Montbell Ul Super Stretch Down Hugger #2 (24 degree) for the shoulder seasons, and a #5 (40 degree) for Summer. It rarely goes to freezing even high in the Cascades, and I find the 40 degree is a very versatile bag.

Just make sure that if you do get a 40 degree bag, that it's a realistic rating. Some less expensive bags (and even synthetic) overstate their rating by 5-10 degrees.

For instance, I found the Campmor 20 degree down bag really was comfortable down to 32 degrees. Actually, at 2 pounds, it's really a great buy, but realize it's only good to freezing or so.