I hadn't started my car for a couple days, but I had to go to work. So I started it and instantly I can hear the sound of the belt flying off.

I opened the hood and saw more condensation than I had ever seen in my life -- not surprising, considering the warm days and cold nights we've had. I reattached the belt, same thing happens. I had to grab a rag and wipe down the belt and pulleys before the belt decided to stay on.

I had some of the worst squeaking I've ever heard, but it went away as it warmed up. By the time I got to the office, it was totally back to normal.

Tensioner, belt, both, or should I just blame it on having a very wet engine?

That is wierd!.

How cold was it overnight?, cold enough to make the belt stiff?.

I can't think of anything else that would make your car throw a belt if it is fine once it'* warmed up unless the tensioner and/or belt are worn.

The alternator will be at full load just after startup, hence the squealing for a while.

Roger.

I'm not sure how cold it was last night, but it did rain a tiny bit; also, the day before, it was near freezing at night and about 65 degrees in the day. The belt wasn't stiff at all.

I've been questioning this Dayco tensioner for a while. I thought it was on its way out a while ago, but then it started behaving. Guess I might have my answer.

I'm pretty sure the squealing was just belt chatter caused by moisture, because I have no bad pulleys and it went away after it warmed up.

it'* going to be a belt or tensioner/belt path issue. Something is up there.

I think your tensioner is the root of the problem, but change the belt anyway unless it'* almost new.
All that slipping won't have done it any good.

Roger.