It's a question I hear a lot from people around Juneau, even outdoors-type people. I think it's because people around here understand that I'm not simply trying to ride in the rain or the cold or the snow, but rather a volatile combination of all three. Weather forecasters call it "wintry mix." I call it "snain." It's seriously wet, right on the cusp of freezing, and a stream of slush is falling from the sky. It mixes with the night snow and day rain to form a putrid, gritty Slurpee that covers icy roads and trails inches thick. Ride through it, and one will have to endure the barrage of a frigid gray geyser that no fenders can hold back. Not to mention there's still Slurpee falling from the sky. It's like that often here, especially in November, December, January, February, March .. well, often. And it guarantees two things: You're going to get wet, and you're going to be cold.
So when I want to ride my bicycle when it's 35 degrees and slushy, I just assume I'm going to get wet. Trying to stay dry is an excercise in futility, and I've been a lot happier since I gave up the battle and turned my strategy to "wet and warm." I've found a system that works really well for me:
Base layer: I like to wear a thick synthetic base, such as polypro and polyester long johns, which maintain nearly all of their insulation capabilities even when wet. I have a couple of wool base layers, but usually don't wear natural fibers when it's wet because they absorb so much moisture; you start to feel like you're wrapped in a clammy towel. (And, yes, I am talking about Smart Wool here.) Synthetics absorb much less water and maintain more of a semi-dry feeling even when they're soaked. Also, they're much cheaper, so you can throw them away when the start to hold onto that lovely laundry-soap-mixed-with-sweat odor.
Mid layer: When temperatures are in the 30s, I need a mid-layer on my torso. I usually wear one of an assortment of polar fleece pullovers, which also maintain most of their warmth when soaked, although these tend to become quite heavy under saturation.
Outer layer: I have an $8 pair of Red Ledge rain pants that I love, although like all nylon products, they only hold rain out to a certain extent, which is to say not very long. What they are really good at is blocking the wind. I rely on my thick polyester long johns to keep me warm. On my torso, I usually wear a plastic jacket, which is a completely nonbreathable jacket made out of PVC. Basically like wearing a Hefty bag. Some cyclists complain about the sweat condensation generated in this miniature biosphere, but since I don't believe it's possible to stay dry, I don't really care about where the sweat moisture ends and the snain moisture begins. It's all the same, wet and cold, and after more than three years in Juneau, I've resigned myself to the fact that moisture is going to seep in no matter what I wear. Rain even finds its way into my plastic jacket, usually through the neck, arms and bottom.
Outer Outer layer: If I am going out for a really long ride, longer than five hours, I will actually carry a Gortex winter shell or another large polar fleece to throw over my plastic jacket when my core temperature starts to drop, which it inevitably does. The wet and warm strategy can only work as long as I am pedaling at a certain level. During long rides, when my effort starts to drop, so does my body temperature.
Head: I release a lot of heat through my head and hands, so I go pretty light in these places. On my head, I usually just wear a fleece ear band. During long rides, I will bring a thin polyester balaclava to throw on when I start to get cold.
Hands: I usually wear fleece liner gloves with snowboarding mitten shells (Sometimes I start with just the liner gloves and throw on the shells later). Like my leg system, these eventually soak through but do well enough to block out wind and hold in heat. On the long rides, I will simply throw my pogies on my handlebars. Pogies are actually perfect for cold rain. They take a long, long time to soak through, so if you want your hands to stay dry, pogies are the way to go. I usually have to go bare-handed with pogies because they are so warm when it's above freezing, however.
Feet: Lately, I have been a big fan of insulated vapor barrier socks like the ones made by RBH Designs. I just wear a wool liner sock with these, and my regular running shoes (which means you clipless types could wear them with your bike shoes.) They do a great job of keeping out the slush water for a long time, and when they do soak through, they still stay relatively warm. I've completely converted to these, over from neoprene socks and booties. If I want my feet to stay completely dry, I wear a pair of NEOS overboots. I usually only do this for particularly long or wet rides, because they're floppy and annoying. I may have to start wearing them more often, however, because I've noticed my frostbite toes on my right foot are particularly sensitive to the wet cold compared to the toes on my left foot, and I should probably take more precaution to avoid further nerve damage (read: trench foot).
But that's just my system. I wouldn't expect it to work for everyone. Maybe there are some out there who still claim it's possible to stay dry while riding in slushy weather. I'm beyond skeptical, but I'd love to hear your strategy.