The weather forecast (when theweathernetwork.com wasn't down, which was quite a while) yesterday said 1mm rain in the morning <5mm rain in the afternoon, and 1mm rain in the evening. Instead, it was raining and blowing so hard I thought I might have to stop somewhere as I cycled home.
At some point, a loose end of the draw-string on the water-proof wrap that I put on my pannier somehow came loose, then blew into the rear dérailleur, where it was severed between the gears and the chain. But not before it did something to the dérailleur, which now constantly drops the chain. This cut my speed in half, and I wound up in the driving rain for an hour.