I live in Montana and am a fairweather runner, so I like to run on a treadmill during the bad weather and once it warms to my liking, I will run outside. Its that okay to do if I'm starting the Couch to 5K program?
Yeah it might be even better because you can force yourself to do a speed longer than you might of had off the treadmill and focus more on that speed. Try doing 20 minutes as fast as you can and go up .1 every time you do it over months start at 5.0 if you really out of shape and go up to 9.0 it will take months. Then do something easy or rest when you are tired.