People are acting like this is a "new" word, but I remember my dad saying it all the time, as in: "Welp, that settles that," or "Welp, it couldn't have happened at a better time."
Apparently it's being used now on social media as a way of signaling "tone," which is a good idea.
According to this Slate.com article, "Welp occurs when someone abruptly closes off the word well—an occurrence known as a bilabial stop, as linguist Ben Zimmer explained to me—and is akin to the similar slang words yep and nope."
Also from that article:
As Grant Barrett, co-host of the public radio show A Way With Words put it, “Give me an American who says well where all others say welp and I’ll reveal that person to be an offworld alien who has failed at fitting in. Probably a lonely alien, too. He’ll need to learn that word if he wants to abruptly start or finish uncomfortable topics, just like the natives.”