Winter is a time of pause, reflection and self analysis. It is one of the times when the Crone turns to face us, reminding us just how mortal we truly are. Stand outside, let the wind tear at your clothes and hair, the cold bite at your skin, penetrating to the bone. Listen to the sound of the snow blowing across the ice, just as softly Her words can be heard: "all things must pass." For these reasons, Winter is a perfect time for purification and cleansing magick. And these are ends to which the snow, ice, and cold of Winter are perfectly suited.
Snow is simple to work with magickally and it's rather versatile. It can be used to cleanse items. Altar clothes, ritual tools, crystals, and candles can all be cleansed in the snow. Just hold the item in your left hand, with your right take a handful of snow and rub it all over the items. Cleansing with snow is like cleansing with a million very small clear Quartz crystals, and that is the affect it has, as well. It leaves the items feeling freshly cleansed, but energized at the same time. Items like tools and crystals can also just be left outside overnight, buried in a snow bank, to be cleansed by the snow.
Snow can also be used in the creation of a "snowbane" for banishing magick. Outside, form some snow into an image of what it is you will to be rid of. As you form the snowbane, fill it with all the energy and power that thing, person, bad habit, or whatever, has over you. Take your snowbane indoors now. Ideally, place it in a cauldron, but a large cooking or mixing bowl will do perfectly. As the snowbane melts, so, too, the power of what it represents has over you fades.
Snow and ice can also be used to intensify energy within your Circle, just be sure to do your ritual at a time when the winds are calm as Winter winds are prone to dissipation. To this end, the snow can be mounded up to designate the Circle boundaries and piled up a la snowman style for an altar and for smaller altars at the Quarters, as well. If you are particularly ambition and like to play in the snow, you could construct a small outdoor temple outdoors, entirely out of snow, much like an igloo. It need only be big enough for you to sit comfortably in and you could create a snow-sculpture inside to represent your deities.
Another idea is to work your spells and rituals in silence, as silence is one of the virtues of the North and, thus, of Winter. Gestures alone are quite powerful and evocative, but, as Winter is a time of introversion, visualization alone can be quite appropriate.