I see more black tail in the rain then the sun-just wait for the good shot,don't worry about tracking

Bob and 5deer are correct. Here in Oregon, if you hunt the late season, you hunt the rain. Get close and good shot placement are the key. Go ahead and get out there! Good luck, stay safe and shoot straight.  

Light rain is OK....your reason for avoiding heavy rain is the same as mine....wait 30 minutes after a shot in a downpour and you'll have no blood trail.