Rivnuts from Homestead, PA on 7/31/2023 9:44:19 AM:
According to historical climatological data provided at weatherspark.com, the "average" daily temperature in Cumberland MD (the northernmost end of the C&O) ranges from 70 to 50F at the start of October to 60 to 40F at the end of October. Less probable extreme temperatures range from 80 to 40F at the start of the month to 73 to 28F at the end of the month. These temperatures generally increase a few degrees as you proceed toward Washington DC. As you can see, the temperatures you may encounter vary broadly both by time of the month and statistical probability.
The daily chance of rain ranges from 20 to 25% which is generally the lowest of all non-winter months.
I would plan to travel as early in October as you can. As I prefer to make the trip and will do so this year in mid to late September, I made the trip the third week of October last year and awoke in my tent to temperatures just above freezing on a couple of mornings. Such a wide variability can cause you to have to carry a broad range of clothing for all possible conditions. i recommend you watch the weather forecasts along the C&O as your departure date approaches to reduce the range of conditions you will expect during your specific trip and, hence, the amount of gear you carry.
Note the amount of daylight hours is 11.1 hours in October if you are planning to ride long miles each day.