Take reasonable precautions, i.e. hold the rifle so it is sheltered or covered by your coat and body as much as possible, keep the muzzle pointed down and you will be fine. Some of my most productive deer hunting has been in a light rain or snow, and my caplocks have never misfired in those situations. I always do the standard procedures when loading - dry the barrel, snap 2 caps, then load, the evening before I hunt, and cap the rifle when and where I hunt.
Good luck tomorrow, I'll be hunting a week from tomorrow.