Mar–May
Desert south hits peak comfort — White Sands gypsum is most walkable now and Carlsbad daytime stays cooler than the brutal summer. North central thaws by April: Bandelier's Frijoles Canyon opens up and Santa Fe shoulders into shoulder season. The high country in the Sangre de Cristos, Wild Rivers, and Cimarron/Valle Vidal still carries snow at elevation through May. The defining hazard is wind — 40–60 mph gusts are normal across the eastern plains and Tularosa Basin in April, blowing tents flat and grounding small aircraft. Cottonwoods leaf along the Río Grande bosque mid-April. Chaco's washboard NM-7950 road is usually solid again by April after winter mud.
Jun–Aug
High country opens — Wild Rivers' Cebolla Mesa sub-units, Black Canyon, Sleepy Grass, Iron Creek, and Cimarron in Valle Vidal become the relief valve. The North American monsoon arrives early-to-mid July and runs through mid-September: daily afternoon thunderstorms, flash floods in arroyos and the Río Grande gorge tributaries, lightning above 8,000 feet. White Sands and Carlsbad daytime highs routinely top 100°F — pre-dawn or post-sunset visits only. The Tularosa Basin around Valley of Fires tops 100°F most July afternoons and can push past 105°F. Gila Wilderness backpacking peaks despite the monsoon, but early starts and ridge avoidance are non-negotiable once cells start building by 1 PM.
Sep–Nov
The broadest sweet spot. Aspens peak in the Sangre de Cristos the last week of September through mid-October — Wheeler Peak Wilderness, Hyde Park, and the Santa Fe Ski Basin road run gold against dark spruce. Cottonwoods turn along the Río Grande bosque mid-October. Monsoon humidity fades by mid-September and dark-sky viewing peaks because the air dries out — Chaco, Wild Rivers, and Valley of Fires hit their best clarity of the year. Chaco's optimum visit window lands here: daytime cool, washboard NM-7950 still drivable. Northern high country closes to first snow by early November and gates start shutting on the forest roads.
Dec–Feb
The desert flips to peak. Carlsbad, White Sands, Valley of Fires, and Aguirre Spring all run their calmest, coolest stretch — 60s by day, 30s overnight. Cloudcroft and the Sangre de Cristos pile cross-country skiing snow in the Sacramentos. Bandelier's Juniper Family Campground stays open year-round at 6,600 feet with occasional snow on the Pajarito Plateau. Chaco's NM-7950 access is generally passable but worse in winter mud — always call ahead before committing the drive. The southern BLM/RIDB sites stay mild: Aguirre Spring at 5,500 feet and Valley of Fires at 4,500 feet rarely see hard freezes.