mporter012, what kind of light meter do you have?
Incident, the kind with a white dome, gives reading of light falling on the scene (so snow or low won't change the meter reading)...
Spot, you would be able to read the snow from a distance then "place" on Zone VII.
Reflected light meter, you can work as if you had a spot meter. Walk right up to the snow. "Place" on Zone VII same as a spot meter when you get close. (Using a reflected light in average mode is OK most of the time but "high-key" and "low-key" scenes mislead the meter)
In-camera meter, same as reflected light meter but I don't like the mental gymnastics required when I go to take notes.
On the subject of N+ N and N- development for roll film. Even my earliest Zone System book agrees with what others have said. Develop (more or less) normally and use paper grades to adapt to different contrast negatives that you might have created on a single roll.
I personally would rather not carry three cameras. So I develop the entire roll to fit what I believe the majority of the (important) shots on that roll would require. It's as simple for me as, "It was a foggy day, I will develop it N+1".
But even the roll I have in the camera now has two different requirements. One outside at daytime and another at night in a restaurant.