I don't usually like to have fires under anything combustible, like a tree or flammable shelter, so I will try to choose a spot that is in the clear, but still near a wooded area to provide some relief from wind. If I must get a fire going in the rain or wind, I will usually first erect a tarp and get as much tinder under it as possible. I will then clear a spot where the fire will be, make a tipi shape cover using pine bows, and go back under the tarp to start a small fire and get a few coals burning, preferably on a flat rock. Once a small fire is going, it is possible to pick it up and move it into the main fire area, where it may be necessary to huddle close shielding the fire with your coat in order to ensure the fire takes hold there. Keep babysitting it until it starts to blaze, and don't be shy to throw a green pine bow it it either. The pine bow acts as a cover against rain, and once it lights up, it goes like kerosene. After the fire gets good and hot, only a deluge of biblical proportions will put it out so long as you continue to feed it. A fire in the rain consumes far more wood, so before you begin, make sure you have a good supply under that tarp! For warmth, I will often move hot rocks under the tarp if need be and use them to keep warm, at least until the rain lets off enough to go stand by the fire for a good duration of time without getting soaked.