GPS is not affected by clouds, at all. It was designed to work regardless of the weather - the war doesn't stop just because it's cloudy. Liquid water, however, will block the signals entirely, and your body is mostly salt water. Your fingers, hands, or head, or torso between the satellites and the antenna will completely block the signals. Metal will also block them, as well as the coating on some windshields. GPS doesn't work well indoors, inside cars, or under/behind your body, and that's not just a problem with the N810, it's a limitation of GPS in general because of the frequencies used.