"Hello, welcome in" as opposed to "Welcome"

Question

In the past year, I have noticed an interesting trend with some of the stores that I have shopped at with my fiance; when you first walk into the store, an employee will be at the door greeting customers and saying, "Hi, welcome in!" I have never heard this expression until this past year or two. Generally, I hear it in brand-name stores like Kendra Scott, Kate Spade, and Coach. I find myself wondering if this is proper grammar, and the etymology of this phrase as opposed to the traditional, "Welcome." Is the "in" added to provide direction or additional meaning along with the phrase? So far the only discussion I've seen that might provide a little insight is here, way back in 2007:

https://forum.wordreference.com/threads/welcome-to-welcome-in.596905/

So is it proper, and where does it come from?

Answer 1

Greeting someone by saying “welcome in,” is hardly a novelty:

I passed by the crowded gate, and though the keeper was preventing the entrance of the crowd, finding that I was an American stranger, the porter said, “Welcome, welcome in,” and opened the gate. — Asenath Nicholson, Ireland's Welcome to the Stranger, 1847.

“Young master elf, welcome in, welcome in all.” He opened the door and ushered them all in, shutting the cold out quickly behind them once they'd entered. — Brad Higgens, Talisman of Blood: Book 1 – Shadow of the Gryphon, 2012, 175.

Welcome in out of the rain! Today the shop is open from 13.00-16.00 and I, Andrea, will be in place to offer corset-related expertise! — PicBon

Welcome in out of the cold once more my friends. Blow a nice warming breath onto your blue tinged fingers, and pull up a stool around the fire. — Tim the Tum blog, 31 Jan. 2012.

What does seem novel is that you’re hearing it as you enter a shop, especially if it’s in a mall, where you’re moving from one climate-controlled space to another. Traditionally, the greeting is given as someone holds a door for you, especially in inclement weather. The in is directional, i.e., accenting that you’re moving past an obstacle or coming in from rain, cold, etc. If none of these apply, then I would imagine the implied barrier guards what the store employees hope is a pleasant, relaxing, or luxurious atmosphere, at least better than whatever is “out there.”

Answer 2

I started noticing it in Seattle about the same time (12.18), also at the mall. My guess is it got mandated in some corporate training and spread like wildfire cause pretty soon I was hearing it at restaurants, Ross, etc.