-40 is the same in C and F... I know this because I grew up in Wyoming. I've seen -40.

At that temp, you can do this neat little trick where you take a pot of steaming water (not boiling, that's a safety issue) and throw it into the air.

It will be snow before it hits the ground.

Again, don't use boiling water, and don't even try it if the temps are above -10 F. Don't throw the water into the wind, that will just splash it back onto you, and if you ignored the "don't boil" instruction, you'll be splattered with boiling water.