Does anyone know if it really matters whether I check the tranny fluid while it's really cold outside?

 

You want to drive the car until it reaches operating temperature first, then park car on a level surface, turn engine off and within 90 seconds check the fluid level. Outside temperature does not matter, just follow these steps. Same thing is stated in your owners manual.

 

The owner's manual reads that the engine should be left to run until the cooling fan starts. This assures that the tranny fluid is at the proper temperature. Only then do you shut the engine off to check the level. Be sure to wipe the dipstick before checking the level. It foams a bit around the dipstick, so gives a false indication if not wiped down beforehand.