Here's what's happened so far:
I told Nikon about the issue, and they sent back with what I wrote above. Then they said this:
"The colder temperature, may have affected the camera as it came inside to the warmer air, like going from cooler air outside to an indoor pool condensation can occur if the camera is not properly protected. If you can see if you get the same issue, if it does occur again, keep in mind the temperature outdoors. Typically it the sudden change in temperature that can possibly cause issues"
And gave me a link on how to care for my Nikon camera... [link: http://support.nikontech.com/app/answers/detail/a_id/16567
Which I kinda resented. I also didn't like that this was written off so easily, so I wrote:
"Is this the conclusion after inspecting my photos or the conclusion based on my account (which could possibly be inaccurate in some way)? I need to make sure that there isn't a defect with the camera. I have two jobs this weekend and can't afford to be plagued with yellow lines in my photos."
Then Nikon responded:
"This is based on the conditions you were shooting in, we can take a look at the camera to verify it is working to factory standards. Please follow the instructions below..."
And tell me how to send it in. I'm kinda ticked off about this. First, it was the cold weather, so it's nothing to worry about. Then I ask, "wait, are you sure?" and they say, "um...send it in." It's like, seriously, we're dealing with a really expensive piece of equipment here that I need to be working. If it does work, I can't afford to send it in, and if it doesn't, I can't afford not to. But arbitrarily saying "no, it's fine" and then "yes, send it in" is so strange to me! Basically, if it happens again this weekend, I'll just have to work with it - but I'll send it into Nikon afterward. This issue is strange all around.
I also tried to reproduce the issue again last night - same memory card, same everything. No signs of any problems. Perhaps it was just a really, really strange fluke? Hopefully. Thanks for the help, everyone!