Winter storms are a unique time to shoot, both during and immediately afterward. They change the landscape as well as show the details of subjects in a different way. These features play to one of the strengths of macro photography, showing the world from a different perspective. However, ice and snow do provide some interesting challenges when it comes to exposure.
First of all, you need to understand how your camera calculates exposure. The light meter in your camera is a reflective meter, meaning it will read everything as though it were 18% grey. 18% grey is the mid-tone range, like the color of green grass for example. The problem is it will also try to make whites into gray and do the same thing with blacks. This leads to under exposed whites and over exposed blacks. For white subjects you need to add more light (a stop or 2) and with blacks you have to take some light away (a stop or 2 as well).
Snow is, to state the obvious, white and ice is clear to a cloudy translucent. Ice also reflects the light hitting it or the light passes through depending on the clarity. Snow also throws a lot of ambient light into the mix because of the reflective nature of white. In the end you have a lot of elements with conflicting exposure requirements into the image.
What all this adds up to is any kind of auto exposure is not going to get you the results you are looking for. Manual exposure is the tool the job calls for. This is a feature found on almost all DSLR cameras and some higher end point and shoot models. If your camera doesn’t have manual exposure you can see if it has the ability to over or under expose your images by a given amount, often referred to as exposure compensation.
Exposure for snow and ice is a balancing act where you are not going to get the perfect exposure for every element in the image. In general you want to find the exposure which gives you detail in as many parts of the image as possible. When you have detail you can do amazing things in Photoshop to bring it out.
For DSLR where you can see the exposure meter take a light reading for the composition you want, working in manual mode. Then add a stop to a stop and a half. Take a frame and see what you are getting. Then adjust your exposure as necessary. In a few frames you will have the exposure dialed in. You will need to do this for every subject you are photographing in conditions like this.
Below are two sets of images I took as the ice storm in south eastern PA was ending on February 2nd. The first image in the set is one with the exposure mode set to aperture priority. I took the first image in aperture priority to demonstrate how the cameras light meter will handle these kinds of situations. Following there are the images with the exposure changes I made. No alterations have been made to the images in the 2 example groups.
Whenever you are working with show and ice your exposure will be continuously moving around. Constantly be checking your cameras built in meter readings as well as looking at your images. If you have a handheld reflective light meter use it. If you have a choose between a little over exposed or a little under exposed go with under exposed. There is a lot more you can do with under exposed images in Photoshop.