Chair Peak offers some great backcountry skiing and moderate alpine ice climbs in winter, and the northeast buttress is an excellent mixed alpine route when the peak is free from snow as well. Compared to the north face, the rock conditions on this northeast route tend to be better. To get there, follow the well-maintained Source Lake Trail from the Alpental Ski Resort (where you can park for free) as it leads down the valley to the west. Continue beyond Source Lake to a larger stream crossing, look for rock cairns and a very faint climber's path, and head straight up. There are several routes that pass large waterfalls; alternately, you can opt to use the more frequented climber's trail that trends west-northwest up slopes that are avalanche-prone when snow conditions exist. Continue to climb and traverse north until you reach the basin below the east face of Chair Peak, then climb the slope and traverse west to reach the beginning of the northeast buttress climbing route; this is a left crack, not to be confused with a faint buttress that is more to the east.
The pitches offer various route options, and the number of pitches will vary according to rope length. Establish the belay position either at the base of the rock buttress below the couloir or scramble up a 60-degree slope to a second belay station with a few slings and a wrap ring. As the couloir narrows the rock becomes loose and there will be minimal protection. Climb the 60-degree loose alpine rock for about 30 feet until the grade approaches 50 degrees, aiming for a large clump of trees that offer numerous belay stations.
For the second pitch, climb to the top of the tree area where you can set up a belay station from the rock outcropping. Climb the 50-degree slope as you look for another viable spot to set up protection, either in the trees or on a rock outcropping. Ideally this will be about 15 feet above the last tree.
The third pitch is immediately northeast of the obvious waterfall. This is a long rope stretch pitch depending on the setup of your last belay. You may find a rusted but solid piton in the rock here, and you can back this up with other protection. This long pitch starts on the buttress crest's 45-degree slope and continues as the grade increases to 70 degrees. Depending on the time of year, snowpack, and precipitation, you may see a significant amount of water coming down here. This may require snow and/or ice protection, but there is generally some exposed rock. Aim for the large rock outcropping northeast of the waterfall. Watch for subtle opportunities for nuts, cams, and pins on the underside of the outcroppings on this pitch. Ideally you'll set up belay after the waterfall on a large root with several slings.
The fourth pitch can also be an extended rope length that climbs directly to the false summit block beneath a large rock and near a tree with a good belay position. Rock protection is limited on this pitch. The fifth pitch can be either a traverse to the summit block or a scramble up to the summit, depending on your comfort level. Be cautious on the ridge as you walk between the gully and the exposed drop on the north side. The sixth and final pitch is a summit block pitch that can head straight up or to the left side for an easier scramble.
Once you are ready to descend, you can either down climb and rappel on the ascent route or down climb the obvious 45-degree snow couloir heading south. While you may feel you are headed in the wrong direction, don't fret; trend east while down climbing the lower section to gain a notch in the main ridge. You'll notice a rappel station at a rock buttress located on the north-facing wall of a rock tower that meets the south side of the notch at the top of a cornice. Note that the rock buttress frequently gets covered in snow. Rappel off here using one or two ropes, as there is an intermediate anchor that will allow you to use a single rope. Rappel 60 meters to the base of the steep couloir, then down the 40-degree slope to the east face. Keep heading east until you hit the approach trail that returns to Alpental.