Because I am cold! So thinking about taking my boat out on New Years and I read cold makes more power, hot takes away. This is true? With jet boats? How much? Teach me! Should be 45-55 degrees out that day. Way different then 100 degrees. Lol

There's some holes in your theory.

Yes,  cold air makes more power. That being said,  cold water can take it away. Also,  cold air is much more dense, which is where the hp comes from,  it's also less likely to provide any lift.

I would call it a wash,  I wouldn't expect bigger numbers just because of the cold air. We used to struggle with the race boat when it was really cold, especially with 40°F water.

GT