Although Yellowstone National Park is open year around, the park is fully accessible only from late May/early June to late October.
The northern section of the park’s roadway, from the North entrance at Gardiner, Montana to the northeast entrance at Cooke City, Montana is the only portion open year around.
Mid-December through early March is winter season, during which oversnow vehicles are permitted on snow-groomed roadways of the lower loop of the park, and from Mammoth Hot Springs to Norris Geyser Basin.
From mid-March to mid-April park crews work on clearing the roads of snow. In early-to-mid April the park’s roads open for about two weeks of bicycle access only.
Lower elevation roads begin opening to automobile traffic in late April, and by about early June, depending on weather conditions, all of the roads in the Park are open to automobile traffic.
Then, depending on weather conditions, higher elevation roadways in Yellowstone begin closing in late October. All roads except the northern section close by the second week of the November. And in mid-December, some park roads, as noted above, open for oversnow vehicles.