Use a pebble tray to keep local humidity up, and mist your tree as often as you can. Temperate varieties include Juniper, Azalea, Boxwoods, Sawara Cypress, Tsukomo Cypress, Andelyensis Cypress, Cotoneaster, Pyracantha, Chinese Elms, Yews, Ilex Pagoda, Holly, Roses, and most Herbs. Cold Hardy Bonsai are varieties which need a full change of season to do well. Gradually decreasing temperatures will put your tree into dormancy, slowing growth and storing energy for spring. When it becomes too cold for your Bonsai to stay outdoors, move it to a protected but unheated area.
Some options are a cold-frame, a garage, and enclosed porch, or a bulkhead.
Be careful to avoid temperatures below 20 degrees. If you suspect that your winter location will go below that temperature, you should mulch your Bonsai in with pine needles or peat moss. When your tree is at 40 degrees or colder, it does not need sunlight, it is fully dormant. When temperatures begin to increase, the tree will begin to wake and grow. Your Bonsai now will be needing more water, and protection from freezes.