One of the most difficult times of the year to commute by bike is during the winter. I spent a relatively mild winter in Colorado bike commuting and used the public transit system when the roads became too icy to ride.
Equipment to ride in the winter is out there: warm clothes, lights and even studded tires to help on snow-covered or icy roads or trails. The greater caution is traffic.
Sharing the road with automobiles when you bicycle has it's challenges in the best of circumstances. When you add winter weather conditions sharing the road can be very dangerous. Ice is not only a danger for riding on two wheels, but can reduce the ability for automobiles to stop or correct if necessary.
I have had to explore alternate routes for commuting and use public transit, such as a bus that can carry a bike, to help commuting during the winter. Investing in brighter lights and a few more safety lights can also help with the shorter days of winter.
I find that I commute by bike less in the winter months, but I know a lot of people who continue to bike. Conditions change in winter for cyclists just like they do for motorists.
For those of you who bike during the winter...stay safe and see you on the road.