I agree with Rod-Knox that 20/50 would work on an older vehicle but not so well on a later model car.
Even with an older car I would never run 20/50 in a cold climate. It turns to the consistency of cold tar.
I would guess the recommended oil is 5/30 or 10/30 all depending.
How frequently you change the oil depends upon the type of driving, dust, humidity, state of tune, engine wear, gasoline quality, and so on.
My Harleys use straight 60 weight and on a cold day one might as well leave the oil container in a funnel and go watch a football game while it drains.