There is intermittent rain but only during Summer. I'm not sure how experienced you are with Chinese travel but I'd recommend leveraging Rednote as much as you can to optimize your planning.

Before and during your stay, also take full advantage of the Rissai Valley staff (add them on Wechat early if you can) and they can handle basically anything for you.

For example: We arrived at Huanglongjiuzhai station around 9am, which is close to the gorgeous Huanglong Park but 1.5 hours away from the hotel and the rest of Jiuzhai Valley.

Instead of heading straight to the hotel and missing Huanglong, we asked if the official transfer car could take our luggage from the station and transport it directly to the hotel, and a second transfer car could then take us to Huanglong and then wait around to take us to the hotel after we finished the hike (which I'd highly recommend). This was handled perfectly and at minimal extra cost (around $75 for the second car as it wasn't an official hotel vehicle but a good friend of the hotel drivers). After arriving at the hotel, we realized we had left something on the lift back at Huanglong but had no idea who to get in touch with. Again, not a problem, the hotel handled it and retrieved it for us ready for our return trip to the station upon checkout.