I just spawned in during the middle of a rainstorm out in a field and I ran around for a bit before realizing that I wasn't getting wet. Not even my clothes were wet and it didn't display a wet icon in the debug monitor or the inventory. I also noticed that my temperature didn't go up or down. Later I made a fire in a barrel inside and stood next to it but my temperature stayed the same.
I'm not really sure if this is a random occurrence or if it was caused by my logging in during the rain. The last time i logged in it was dry and later starting raining which caused me to get wet and cold. I've attatched screenshots of the monitor and the inventory during light and heavy rain showing no change, and one by the campfire. In all three my body temp is 37.22.