It was raining, of course, this past Sunday when I went to the track for my second run since breaking my wrist while running last fall. (First having been Thursday.) I've previously talked about running with lightning (i.e., don't!). But my negativity about being electrocuted* should not be taken to apply against running in the rain. A number of my favorite runs have been in the rain. Probably a higher fraction than in 'nice' weather.
Running in the rain becomes pleasant once you make some attitude adjustments, and perhaps do some physical preparations. Bonuses are that you can congratulate yourself for your tremendous virtue in being out in spite of the unpleasant weather. And if you race, it's a plus because even though you could arrange to do all your training in nice weather, you cannot ensure that all races will have nice weather.
The main attitude adjustment is one suggested by a fellow trail runner. We were going to run on trails during moderately heavy rain, after 2 days of steady, heavy rain. Our path was all dirt except for a stream crossing. In other words, after all that rain, no question that we were going to be soaked, and muddy, and soaked again (by the stream). As he said, it was time to let our inner child out to play -- splash through the puddles (which were numerous) and enjoy the mud. I won the contest for having the mud highest on my body (up near the shoulder blades) without having fallen.
Physical preparation starts with the fact that you are going to get soaked. So relax about that part. During the run, get wet and don't worry about it -- assuming that you're not running with too little clothing on, and temperatures are low enough to make hypothermia an issue. (If that sort of thing is a consideration, get out of the rain immediately.) But a spring rain, like I had Sunday, with a warm house or car nearby, and adequate clothing ... enjoy. The thing is, have two sets of clothes. One for running in, and one for immediately after you finish running.
Your clothes for the running should be what will soak up the least water. Go for your shortest socks, shorts, shirts, ... that will still be warm enough. You'll need a little warmer clothing than usual because the rain will be cooling you down. If you have clothes that are rain resistant, such as a waterproof nylon shell, they're good ones to go for. Regardless of that, avoid cotton. It will soak up water by the pound. Rainy days are your days to appreciate technology -- go for the nylon, polyester, tech fabrics for your tops and bottoms. Be sure, though, in reaching for your nylon shell that it does breathe, otherwise you'll boil. (Or at least I would; I generate a _lot_ of heat when I run. Corresponding amounts of sweat once temperatures break 20C / 70 F.)
The longer your run, the more expert you should be in what to wear before you take up the rain running. 30 minutes in moderate temperatures doesn't require particular expertise. 3 hours in near-sleet conditions (yes, I've done that) requires a fair amount of previous practice.
After the run, it's fairly obvious what to do -- change in to dry clothes. But apparently not so obvious that some hundreds of runners at a race of a couple thousand managed to remember it. This was a 10k race a number of years back that I finished ahead of a lot of people that I normally didn't. My rain training was current, and I knew I had a checked bag of dry clothing, and a towel or two, waiting for me at the finish line. So I relaxed in the race, cruised down the highway, and actually ran my fastest 10k ever, in spite (because?) of the rain. At the end of the run, have a sheltered area to change, and change in to those nice, dry, clothes after towelling yourself down.
The only novelty I'd add is that you want to aim for layers of clothes so you can pull on more as you cool off from the run, and to have more layers available than you ordinarily would for the temperature. This latter is because you will have lost more energy in the run than your normal -- all that rain will have its effect at sucking out your body heat. As your metabolism relaxes from the during-run furnace levels, you'll welcome that extra shirt or sweats.
One thing I've never worked out is what to do for/with glasses. I'm fortunate in being able to run without mine. If I'm surprised by rain on a run, I just (and have to) take them off. Anyone have good solutions here?
*Nobody will get credit for puns, or complaints about them, for/about that comment of mine. Only punsters with low standards would count that one.