Claret cup cactus flowers blooming in mid April. Spring, Summer, Fall, and Winter - Zion National Park (U.S. National Park Service) As the daylight and warmer weather return to Zion, the trees begin to grow leaves and the earliest wildflowers begin to bloom. Daytime temperatures are warming but nights can still be cold. The daily temperature swing can be 30°F or more. Depending on the amount of snow we received over the winter, higher elevation areas may still be inaccessible without winter gear. Snow begins to melt and raises the level of the river so the Narrows may be closed for an extended period of time.