I just heard a faint rumble of thunder outside and went to the window. Yep, spring thunderstorms coming up. The last few days have been rather warm, and convection has kicked in.
What did a wandering storyteller do when it rained in medieval Wales? (I say "when," not "if," advisedly!) It seems to me that he had three choices: (1) find shelter, (2) get wet, or (3) put on the medieval Welsh equivalent of a raincoat and hope for the best.
Choice #1 would be good enough for a sharp, short shower, but in a prolonged storm you could get hungry (if sheltering under a tree, rock, or some other natural feature) or wear out your welcome (if you had been lucky enough to find a house). The last time I was in Wales it poured for several days in a row. Fortunately I wasn't on a walking tour!
Choice #2 (get wet) would have happened fairly often, but it isn't fun, and would motivate anyone who could to avoid it. That leaves choice #3. What did the medieval Welsh use for raincoats?
The collection of manuscripts called the Law of Hywel Dda has an interesting section on the distribution of old clothes. One item mentioned is "the King's [old] rain capes, in which he rides." The Groom of the Rein is entitled to these, but unfortuately no detail is provided on their construction. My personal guess would be oiled leather, but that's only a guess - examples of something similar have been found in Danish bogs.
There are also records of woolen cloaks, sometimes very shaggy ones, worn by the Irish. Assuming the natural lanolin was left in the wool, these might keep you reasonably dry, or at least warm - wool has some insulating value even if wet. Some sort of British cloak was also mentioned as being imported by the Romans, and may come in the same family. And then there's the Orkney Hood. Possibly British, possibly Pictish, possibly who-knows-what, it wouldn't keep all of you dry, but you would look stylish.
And that has to be worth something!