Weather in Yellowstone NP in Late September

TenOC wrote:
Best time to go. But be prepare for snow. I would say about a 10% chance.

Stop at Gross Ventre at Grand Tetons and see the moose but NOT this close Note the date on the photo

Do not get this close to these animals. Yellowstone is not a zoo. These animals can be very dangerous. One or two people a year are killed because they think these animals are tame. JMHO.

If you don't want to see snow, don't go to Yellowstone. I have seen it snow every month of the year there, honestly. It's higher and further north then you are used to.
But late Sept, odds are it might snow, but the snow will be melted off the roads by noonish, If it's an unseasonable storm the Park Service will actually plow the roads.
Personally I prefer the early spring, as the game is largely still down in the valleys. But Sept is a good time, being the Fall some of the big-game will be more aggressive then earlier so make certain you give them space.

Best time to go. But be prepare for snow. I would say about a 10% chance.

Stop at Gross Ventre at Grand Tetons and see the moose but NOT this close Note the date on the photo

Could be warm, with a chance of snow. Temperatures will vary from freezing to the mid 70s.
Good time to go. Elk should be passing through Madison campground bugling all the way in the evenings. Bears could be passing through Fishing Bridge.Trees will be changing.