2003 Ford Taurus Belt Squealing

I have a 2003 Ford Taurus that is squealing very loudly. The squeal is obviously coming from the belt. I checked the belt and I do not see any noticeable problems; it is dry, clean, no fluid leaking onto it. The pitch is very high and loud. It is winter here and recently the weather warmed up considerably but is now back around freezing. I did not drive it much during the winter. This problem used to only happen when it rained, and the squealing would stop after a short while. Now, the belt is perfectly dry but the squealing is very loud. How do I fix this squealing?