Rivnuts from Homestead, PA on 9/29/2024 8:53:48 AM:
Given you are starting tomorrow and no rider on the trail at present has responded I'll provide what information exists (which you probably already have) along with my experience living/riding along the GAP and several rides on the C&O over the last 10 years.
There's a light rain in Pittsburgh this morning and is forecast to continue most of the day today as well as tomorrow morning. Tuesday and beyond look dry with clearing skies. As a result and excluding the first 20 miles on pavement leaving Pittsburgh, the GAP with its crushed stone will likely be soft with an occasional puddle or two.
Looking at Cumberland, a more steady rain is expected today with more rain and showers on Monday and Tuesday before clearing the rest of the week. Thus I would expect some sloppy conditions on the Towpath with puddles and some mud, especially between Cumberland and Spring Gap as well as between Paw Paw and Little Orleans where there have been no trail improvements made. The balance of the Towpath in route to DC where new surface improvements have been made may be a little soft but decent with improving weather and some sunshine to aid in drying out the trail.
Those would be my expectations if I was undertaking your trip tomorrow. Hopefully, someone on the trail presently can give you real time info. Enjoy your trip and be safe.