This is fairly obvious for most situation. It is common sense. In a very light tail wind less than 2 or 3 MPH, it is possible to take off from a mountain launch in a Paraglider, but you need to have excellent running ability. If you attempt to take off in such conditions, you should make sure that the wind is not subdued because of blockage from Trees or obstructions. This means going to the upwind side of the Mountain or hill and confirming that the wind is truely light. For the most part, taking off in a tailwind is a bad idea.