What Hobbes says jives with what I've head other growers say and some casual rain probably not an issue but a deluge during your harvest week might hurt it some. Different strains produce different trich types. I've read, sativa produces the bulbous or glob type, indica strains the long stem with bulb on the tip(can't think of the names). So an experienced grower was saying he pulls even a week early if he expects a lot of rain because he's an indica guy and the rain can effect those trich types negatively, whereas sativa type not so much an issue because they don't produce those photogenic trichs we're all used to seing in macros and his theory is they withstand the force of the rain better. His point of view was from his experience the short stalk glob-like trichs sativas tend to produce aren't affected much by rain but the pretty ones with the "bubble" on the tip can be and that's mostly in indica/indica crosses. I don't know if that's true or not but remember pulling a skunk(mostly sativa) and being disappointed by a lack of frost and that it had mostly the glob like trich glands even though the smoke was still pretty good. So what he says seemed to have some credibility. Even though we see mostly the trichs with stalk and bubble-top on pics that's probably that nobody wants to take pics of theirs if they don't produce that kind of photogenic coverage. I know I've seen an article showing the difference types of trichs and their are about four. This guy's "proof" of heavy rain at harvest effecting potency was anectdotal from years of growing experience where he tends to harvest in stages and the difference in potency between parts of a plant he harvested at one stage a little early between some he harvested on time but just after they had been rained on heavily. He said he always found a potency decrease in the ones that got rained on heavily right at harvest so he's very careful to harvest even a little early if rain is coming. So some rain a few weeks before harvest wouln't seem to be an issue especially if the sun comes back strong giving the plant a week or two to recover. Another thing to consider is even though trichs are waterproof a real hard cold rain would have a different effect than a lighter warm rain. Anyway, just food for thought.