Climate
The large elevation variations in the forest preclude universal, concise statements about climate. Snow and freezing temperatures at least at night are possible year-round on the high summits; shirtsleeve weather is common in the winter at the lower elevations. About the only common denominator is that springtime is windy and relatively dry.
Broadly, the higher elevations say above 8000 feet, or 2400 meters have conditions typical of continental mountain ranges, generally somewhat warmer and drier than the similar ranges of Colorado. Snowfall during winter is wildly variable, but normally covers the high peaks above timberline and persists through spring, commonly closing many campgrounds until May or so. Many hiking trails in the high country still have snow on them in June. Spring is warm and dry, with a gradual onset of thunderstorms starting in June and building to a "monsoon" condition in August. The high peaks are notoriously prone to lightning strikes; if you're hiking, make sure you're off the summits by 1 p.m. during the summer. Fall is clear, crisp and delightful, with the first significant snow usually in October and the first snow that "sticks" frequently occurring around Thanksgiving.
The lower elevations are semi-arid, and winter snowfall is even more variable than at higher elevations. Some winters have seen individual storms that deposit over 40 inches 1 meter of snow, while in other years, winter passes without this much snow falling in the entire season. Low temperatures can drop below zero Fahrenheit. Spring is warm and dry, sometimes downright hot -- high temperatures can reach 90 F 38 C or higher -- and dry conditions persist deeper into the summer than in the higher elevations. The monsoonal thunderstorms begin to drift off the mountains in July to cool and soak the lower elevations, until the warm, dry fall conditions begin soon after Labor Day.
Flora and fauna
The forest is predominantly coniferous, with piñon/juniper "scrub" at the lowest elevations that gives way to ponderosa pines mid-range and spruce/fir forest higher up. Aspens are intermixed with the conifers above about 8000' 2400 meters and provide additional color, particularly in fall. Timberline is unusually high at 11,500'/3500 meters or even higher. Many of the higher peaks are veritable gardens of alpine wildflowers once the snow has melted.
Black bear and deer are common throughout the forest. The eastern unit contains bighorn sheep some of which have become so used to human presence as to constitute a camp pest, and a substantial elk population splits time between the western unit and the Valles Caldera National Preserve in summer and Bandelier National Monument in winter. Mountain lions live in the forest but are rarely encountered. Birds are plentiful and diverse, including eagles, wild turkeys, and several species of hummingbirds. Most of the terrain is too high for snakes to be abundant, although rattlesnakes are occasionally seen as high as Pajarito Ski Area near Los Alamos, elevation 9500' 2900 m. Watercourses tend to be small and seasonal, so that there are few large fish, although some lakes and streams are able to sustain a population of trout.
Landscape
The national forest includes many of New Mexico's highest mountains, although the very highest are in Carson National Forest immediately to the north. The Sangre de Cristo Mountains are in the eastern Santa Fe part of the forest, while the western Los Alamos part includes much of the Jemez Mountains. Elevations range from about 5300' 1600 meters up to 13,102' 3993 meters at the summit of Truchas Peak.