T. “You really helped me prepare for the shifts in temperature when backpacking.”
Backpacking between late July and early October allows you to explore the Olympic Wilderness. That said, your exploring is most likely exposed somewhere between elevations of 2,000 and 7,000 ft. As a general rule you loose 3 degrees for every 1,000 feet of elevation either going up or down. For example, if you started out at 2,000 feet and 55° F, and hiked to 6,500 feet; at days end you’ll set-up camp at about 41°F. That is 13.5° cooler than when you started. On hot days if you are traversing facing west or south the drop in temperature is even more extreme; traveling east and north are far less exaggerated by less exposure to the sun. Always carry layers, putting them on or taking them off as you attend to the temperature.