The first? Am I just misremembering or did we not have these before the last few years? I don’t ever remember hearing this term before the 2020s. But now we’re just taking for granted that there will be multiple?

ReneeF: 1st this season. Origin:Atmospheric river - Wikipedia

Oof!

Ok so the term is from the 1990s but the phenomenon is older. It just wasn’t named before. But they are getting “slightly” more intense recently.