There is indeed a difference, but you wouldn't know it from listening to these breathless announcements every night.
What I hate about these particular (nearly verbatim) examples is the summing of the entire population of every state that might be touched by a system and barfing it out as if it's a body count.
And why all of a sudden does every weather phenomenon (or variant thereof) have a new sensational name?
And on a California-centric tangent: I also detest meaningless labels, which CA loves. For example, there's a RED FLAG WARNING! WTF is that supposed to mean? Are millions of people threatened by red flags? OH NOES!
And finally there's "sigalert." Insert giant eye-roll emoji.
The atmospheric river post would be an example of the second headline and should still maintain the necessary urgency and implied danger.