There is no reason why you cannot carry on enjoying running when the winter draws in but its important to keep warm while out in the cold air. To start with wearing shorts is probably not the best idea, so invest in a good pair of leggings. They are not just for women and you will find they are more beneficial due to less friction when running and stimulating blood flow. Secondly, a base layer upper garment will make sure you are kept warm and needs to be tight fitting. Lastly, you must wear bright, reflective or fluorescent outer clothing to make sure you can be seen by other road users.