White Sands National Park in December

October through April is your sweet spot. Summer temperatures hit 100°F regularly, and that reflective white sand makes it feel even hotter. Plus, summer brings monsoon season with flash floods that can close trails. Winter offers the best hiking weather with daytime temps in the 60s, though nights can drop below freezing. December and January see the fewest crowds, but you'll miss the longer daylight hours. March and April are perfect - mild temperatures, wildflowers blooming around the dunes, and reasonable crowd levels. Avoid Memorial Day through Labor Day unless you're a heat masochist. The park gets busy during full moons when they offer ranger-guided moonlight walks, but honestly, experiencing these dunes under moonlight is worth fighting the crowds. Check the lunar calendar and book those moonlight programs early.