Mid to late August from Roosville can be hot in NW Montana so no snow to hike through unless there is an early snow storm. More thunderstorms likely as well due to the heat rising. Water sources will be at their lowest so plan accordingly by carrying extra in the Basin in Wyoming.

By the time you reach the highest points in Colorado early winter storms could be a problem on the passes above 10000 ft. assuming a late September time frame. With luck you could have ideal weather all of the way but just do not count on it and be prepared for any extreme and know your limits. And remember that hunting season opens in the Fall so be visible so not to be mistaken for a deer or elk.

I only encountered a small percentage of the Divide Riders going South to North.