The pop star touched down in Green Bay Sunday ahead of Sunday's big NFL matchup -- and it looks like she's dressed for the snowy weather out there ... rolling into Lambeau Field with a bright red trench coat and looking all bundled up alongside Brittany Mahomes.

We're in December now ... and the temps have certainly dropped from when she was hitting up TK's games earlier in the fall. Gotta rock the right gear this time of the year ... it's chilly.

Anyway, TayTay and co. had themselves a nice private box suite just like they usually do -- but it was way harder to see her this time around as the camera panned to her ahead of the broadcast ... y'know, on account of the heavy snowfall and all. Still, she was there!

In fact, Taylor's been hanging out with Travis this whole past week -- and there's even a photo of the two of them circulating online that appears to show them at a holiday party.

It just shows how serious they are ... as soon as she wrapped her gigs in Brazil a week or so ago -- she jetted on over to Kansas City and has been with her boyfriend ever since ... including right now, which feels like old times yet again.

We haven't seen Taylor attend one of Travis' games in a minute -- but that's just because her schedule got really busy. It seems like whenever she can, she'll be there front and center.

It's funny ... some people have noticed that Travis actually tends to play better, objectively, whenever Taylor's in the building -- so people will definitely be looking to see his stats today.