Glade to see some of my fellow Washington State people spoke out here, rain, humm yes we get it and if you want to ride in this state you will have to ride in the rain.
First keep yourself dry have rain gear on your bike.
Next rain ex for your visor will help out.
Paint marking are like ice along with manhole lids avoid or go over with little to no lean angle.
Slow down for the corners, tires these days have great traction, but your sight is so reduce you need to keep the pace much slower.
Be smooth, no quick changes.
Keep out from behind big trucks or heavy mist, you will not be seen there, bikes just disappear.
Use cars to be seen, what I mean by this is bring a car in close behind you and use it as your break lights and buffer from the traffic behind when slowing down, the car has to know your ahead of it, it does work out nicely, samething by following a car. Make sure it's a small car so you can see right over the top, the mist is minimal on those cars too.
Best thing is just don't ride that day.
