In May, 3 of the 8 parks we've hand-reviewed are at their best: Grand Canyon National Park, Yosemite National Park, Zion National Park. The table below shows every reviewed park's May verdict, with real temperatures and crowd levels.
| Park | May verdict | Temps °F | Crowds | What May is like | Best window |
|---|---|---|---|---|---|
| Grand Canyon National Park | Best window | 72° / 40° | busy | Warm rim days before the inner-canyon furnace arrives | April–May & September–October → |
| Yosemite National Park | Best window | 73° / 46° | busy | Waterfalls at full thunder — the classic Yosemite month | May–June → |
| Zion National Park | Best window | 83° / 52° | peak crowds | Ideal temps — and near-peak crowds; book lodging early | April–May & October → |
| Rocky Mountain National Park | Good | 62° / 35° | moderate | Elk calves appear; Trail Ridge Road usually plows open late May | June & September → |
| Yellowstone National Park | Good | 58° / 33° | moderate | Bison calves and bear watching at their best; some passes still shut | June & September → |
| Great Smoky Mountains National Park | Good | 77° / 52° | busy | Lush green; firefly-lottery applications open (for June) | June & October → |
| Acadia National Park | Shoulder | 64° / 44° | quiet | Quiet coast — ocean still cold, fog common | September–October → |
| Glacier National Park | Shoulder | 63° / 38° | quiet | Waterfalls roar; the alpine is still buried | July–September → |
CROWDS: RELATIVE SEASONALITY FROM NPS VISITATION STATISTICS · TEMPS: APPROXIMATE NOAA NORMALS AT MAIN VISITOR ELEVATION — HIGH COUNTRY RUNS 10–20°F COLDER
Out of the 8 parks with a complete month-by-month review, May is the editorial best window in: Grand Canyon National Park, Yosemite National Park, Zion National Park. Crowd levels follow NPS visitation statistics and temperatures are NOAA normals.
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