If you are truly a die hard streamer fisherman then you will likely have spent a few days testing out that expensive raincoat you shelled out a few bucks on to keep you dry. And if you haven't, well then lets just say that you aren't dedicated enough. Because truly the rainy, crummy, overcast, crappy weather is just what the doctor ordered for a die hard.
There's nothing that I look forward to more than a warm, overcast, rainy, drizzly, gray day for heading out to the river to try my luck with a few pigs - because that's when they feed. Now of course all rules were meant to be broken, and you'll see plenty of pictures of big fish caught on bright blue bird sunny days, but those are the exception, not the rule. Plus if you're looking for more than a needle in a haystack, it helps to be out on a day when those fish are feeding actively.
Gray days provide that cover that fish are so often seeking out. Whether that cover is vertical in the way that they orient themselves to the bank and current in the water, or if it's horizontal cover with trees, bushes, undercut banks etc fish are constantly in seek of cover. Thats where the gray days provide the ability for fish to move around without being as open to predators that don't do well flying in and seeing in rainy overcast conditions. That's why those streamer days are so good on overcast rainy days, because the fish are moving around and munching happily.
So the next time you're sitting at your desk, in your house, or wherever you might be lamenting about the fact that it's "another rainy Memorial Day Weekend" you need to wipe the sand out of your hoo hoo and put on your waders, grab a rain jacket, and a stick and head to the river to nab a few streamer eaters...