B.W.O., Baetis, etc., etc.
Whatever you want to call it, the Blue Winged Olive (slang for Baetis) is the bread and butter for our trout and salmon. Not only do they hatch at times prolifically, and are the first mayfly hatch out of the gate, but they seem to prefer those cloudy, rainy days to do their business. In other words, perfect days for fishing.