Summer is the main visiting season. Summer bus service begins May 20 each year, although the entire road is not open to buses until June 8. Transit buses operate through the second week after Labor Day each year. The exact day bus service ends will vary year to year. Sightseeing by bus on Denali's sole road is a major activity in summer. The days are also at their longest in summer, with the solstice in late June offering over 20 hours of daylight. The summer sun provides so much light, the Aurora Borealis is unlikely to be seen until late August. As daylight hours rapidly decrease in the fall, however, chances of seeing the Northern Lights increase. The spring season in any year is dictated by weather. We begin plowing Denali's sole road no later than March, so ideally visitors can drive up to 30 miles into the park by early / mid April. However, heavy snow can fall in April, so vehicle access in the park is variable until more reliably warm weather arrives in May. There are typically no ranger-led activities until May 15, so the main activity during an April or early May visit is sightseeing along as much of the road as weather allows you to drive. The annual Road Lottery event always occurs the second weekend after Labor Day, after transit bus service ends. This is an event wherein winners of a lottery system may buy a permit to drive the entire road (if weather allows) on a specific day of that weekend. Applications to the lottery are accepted in the month of May for that fall's lottery. Operating Hours & Seasons - Denali National Park & Preserve (U.S. National Park Service) Summer: May 20 through mid-September.