I used to have a goretex mountaineering jacket with a hood that I would put under my helmet when touring in heavy rain. It is what I had and it did the job but it was not terribly comfy in terms of being able to move around your head. But when touring the jacket had multiple uses, so, it was acceptable even if not recommended....

I use a Showers Pass hemet cover these days and as far as I am concerned, it cannot be beat to keep your head warm and dry. A real lifesaver.