By May snow is uncommon but not impossible. Days are usually warm and sunny. Summer birds such as grosbeaks, tanagers, and flycatchers return. Wildflowers and butterflies are abundant. Daytime temperatures in May are warm but rarely hot. Nighttime temperatures can still be cool. Lingering snow and ice is gone from most trails except at the highest elevations. Visitation is moderate with many school groups and tour buses. The parking lots sometimes fill over this holiday weekend.