I have a couple of Rain Suits bought at LL Bean. I keep one in a closet in Shul, where I also have a suit bag with a Shabbos Suit, shirt, Tie, socks, underwear and a pair of dress shoes.
If It’s pouring when I’m planning to leave for shul, I wear sweats under the rain suit and boots, when I get to shul I change. If it’s pouring when it’s time to leave shul, I take off my suit and put on the rain suit I keep there. The key thing is to remember to take the items back to shul during the week.
Twice in the past 10 years weather has been so bad that I have had to stay in shul overnight because of rain or snow. Here in our small town there are no sidewalks and I live about 2 miles from shul.