According to the U.S. Department of Energy 1 ton of anthracite equals 1.4 cords of wood. (hardwood, seasoned). I had a link to the page and the page before that but they keep changing it..... wonder why?
Anyhow I guess I',m off to hunt it down again.
Anthracite coal can be stored practically anywhere, moisture has no affect. You could if you wanted to throw dripping wet coal on burning fire and it will ignite almost as fast as if it wasn't wet.
I usually reccommend putting it on a tarp at the very least. This reduces waste and makes for easy clean-up if your storing it directly on the ground.Additionally a tarp over the top will keep the snow out and keep it from getting frozen together. The tarps aren't necessary, they just make it easier.