Portland, Beaverton, Tigard, Oregon City, Salem, Astoria, and Independence bar "loaded open carry", the maximum they are allowed to by Oregon state law. Portland also claims that a loaded magazine carried outside the weapon is barred, but the legality of that is debated in open carry circles. In those cities, you may openly carry an unloaded weapon without a permit.
Other than those listed cities, loaded open carry is legal. (Although you will likely draw police attention in ANY decent-size city/town in Oregon, loaded or unloaded open carry, except possibly Pendleton.)
With a heavy coat, a leg holster is your best bet. Anything on the waist is too likely to be partly concealed with anything but a very short jacket.