There are many threads related to means to dry firewood. So yesterday I was cleaning up and had a small pile of 1.5 inch rounds of ash sitting up of the ground, but not covered. Sunniest spot in my yard and windiest. 10 feet away is my wood lean to area, luckily with a few pieces of the same vintage and size ash. I set them both in the wood furnace yesterday, a foot apart. The amount of water that came out of that little twig was shocking. The other round did not sizzle at all. A 6 inch round of ash went in and did not sizzle either. Top cover top cover top cover!!!!!
Rain water doesn't really bother dry wood per se. However the rain water really does soak into the bark and the area between the wood and bark. Top covering prevents that from happening. Especially important with small rounds because they are enclosed by the bark. Nowhere for rainwater to escape except the ends.
I burn rounds up to 12 inches, but my stuff is all covered and aged. I just did this as a quick experiment. I see many people that dust snow off the piles etc as they burn. I cannot imagine how they wood must burn or more likely just smolder.
If in mid-winter dusting the snow off there is no problem. However, wait until that snow is melting can be another story indeed. Still all in all it is best to top cover. The picture below has wood covered with old metal roofing.
Branches don't dry out that well. The small ones like 1.5" just take longer to dry. The bark holds the moisture in.
I try to keep everything down to the one inch to two inch size, but I might stop at 4 inches. Little stuff just isn't worth it. I love the 10-12 inch full rounds though. Three of them and the house is warm all night.
After 1-2yrs outside, my seasoned wood goes into my woodshed for another year. During the summer the inside gets to about 100F with the metal roof.....By the time I need it...it's ready to burn...