In early October, I joined a small group heading up to Rainy Pass. When we met at the park and ride in Lynnwood, the weather was perfect for hiking -- temperate, with a clear blue sky and some puffy white cumulus clouds.
When we stopped at the Washington Pass overlook, it was 28 degrees.
When the sun set fully, it got cold.
Fortunately, we set up camp before the cold really set in, and the Lone Pine campground has fire pits, so we had a nice warm campfire going. We spent most of the evening close to the campfire in the interest of staying warm.
Overnight, the temperature dropped down to the low teens. The jacket that I left in next to me in the tent had frost on it when I awoke. After a hot breakfast with some hot coffee and a lot of time around the campfire, we packed up and headed for Blue Lake.
On the way up, we hiked pretty quickly in the interest of staying warm. Once the sun crested the high ridges, we felt a lot better. We ended up relaxing on the shores of Blue Lake for quite a while.
This is autumn in the Pacific Northwest... rugged, beautiful, and decorated with blue lakes and golden larches.