The weather in the Pacific Northwest can be wildly unpredictable. There is a joke here: “If you don’t like the weather, just wait five minutes”. Unfortunately sometimes the opposite is true too!
When packing for your vacation, whether it’s winter or summer, make sure to pack to accommodate various weather conditions. A 90 degree summer day may have a 50 degree evening, followed by a day with a high of 60. The 10 day forecast is reasonably accurate though, so please check the weather before you come to pack accordingly. Layers are always a good idea as a cool crisp morning often turns into a hot afternoon and then after playing in the sun all day when it cools back down to 60-65 degrees, a pullover or windbreaker is extremely welcome.
Scotlyn Ranch has its own weather station on Wunderground: https://www.wunderground.com/weather/us/id/kamiah/KIDKAMIA4