I would at least bring 1-2 pair of pants. Next weeks temps look close to 60 at night but some are dropping in the 50's. When in the parks there is not heat. So if its 55 outside, its 55 everywhere. No heat in the park restraunts etc. Hotels have heat, not the parks.
With the way weather fluctuates I always pack for 10 plus or minus the current forecast. Cause sometimes the weather gets down right cold. Layer a light jacket with a sweatshirt as aback up.