Rivnuts from Homestead, PA on 4/20/2024 10:36:18 AM:
Here are some objective data to consider. Of course, your decision may well be influenced by whether you plan to camp or stay indoors along the way.
Here are the monthly average high and low temperatures for September and October in towns along the GAP/C&O:
Pittsburgh: 75/55 and 64/44
Meyersdale: 73/47 and 50/29
Hancock: 78/53 and 67/40
Note the average monthly rainfalls in Pittsburgh in September and October are 3.02 and 2.17 respectively.
Comparing specific daily average high and low temperatures on and around October 15 are as follows:
Pittsburgh: 9/15 76/56, 10/1 69/49, 10/15 64/44, 11/1 59/39
Meyersdale: 9/15 73/48, 10/1 66/41, 10/15 61/36, 11/1 55/32
Subjectively and from my experiences, I believe that to have the highest probability of having an enjoyable trip is late September. Once into October, there is higher probability of having one or more days of extreme temperature range. October can be quite lovely fall travel but there is also greater chance of having some uncomfortable days. Some miserable cold days made worse by rain or even significant snowfall in the higher elevations are not unprecedented especially as October progresses.
Your decision may well rest on your preparedness and acceptance of the conditions you may encounter.