As the cold weather moves in, earlier than usual here in MN, it gets a bit tougher to find the motivation to run. One thing that always helps me is running for a purpose, and often times it is for a personal goal which is a great motivator. If you are still in need of more motivation running for a cause and to help others is a great reason too. There are plenty of opportunities out there to do so, see article from Runner's World, and if there isn't create your own ask people to sponsor you for a charity in your next race, there are tons of ways to incorporate running into a worth cause.
Charitable organizations from RunnersWorld.com