Edit: Nevermind, found it. Here's a good article with the filming locations
http://movie-locations.com/movies/t/Ten ... ations.php

Minor final act spoilers.

Ok, there's a shot (in the final film) of helicopters carrying shipping containers of soldiers, flying among a mountain range with patches of snow.

We know the final set piece was filmed in Eagle Mountain, California, representing where snow makes sense.

Eagle Mountain is in a Southern California desert. It's located just east of Joshua Tree National Park, where snow is reportedly rare, albeit possible. The helicopter shot brought my attention to the snow in my most recent IMAX viewing. I paid attention for snow in other shots, and there are a few wide shots that we get early into the Eagle Mountain set piece that has patches of snow in the background.

I'm combing through photos of Eagle Mountain on Google Images, and cannot find a single one with snow.

So for Tenet, did Nolan (a) get lucky and happen to film at a time with real snowfall, (b) add it in post, or (c) have his crew place fake production snow in the background?

I'm not sure what the chances of Option A are. The odds of option B is, of course, less likely for a Nolan film. So if he really did have practical snow, holy crap, that snow was all over the mountains in some shots, especially prominent in the helicopter w/ shipping container shots. Crew had to have gotten that snow up there somehow. Maybe by helicopter drop? Or could you imagine being on that crew, and the set designer being like "Hey, Mr. Nolan needs snow on these mountains. I'll need you to hike up there and scatter this fake snow around."