As the weather starts to get colder and the days shorter, it's time to make a few changes to your routine to stay comfortable, healthy, and safe while training through the winter. The first priority in cold weather is staying warm. Clothing choices and a proper warm-up prior to exercise take more careful consideration than they normally do in the summer, when the only effort required to break a sweat simply involves taking a few steps outside.
In regards to clothing, layering is a very effective way to stay comfortable as your body heat rises during a run. Multiple layers of lightweight, synthetic fabrics can keep you warm and comfortable throughout a wide range of temperatures. Even adding a light windbreaker can make the coldest wind comfortable enough to keep you outside and training. Avoid cotton materials as cotton is a very poor insulation material when wet.
When the temperatures fall, joints and muscles also tend to become stiff and lose their elasticity. Don't forget to spend a few minutes warming up prior to starting out. Rather than sprinting out the door at top speed, spend a few minutes doing proper stretching and start out a little slower. This allows the body's temperature to rise and muscles to properly loosen. Walking lunges and leg swings can be very effective at quickly loosening up muscles prior to a run. Many good, dynamic stretching routines can be found online, and should include stretches for your hamstrings, hips, and calves.