The country around San Rafael sits at 6,500 feet — high enough that summers are warm but not punishing, and winters are cold and snowy. May, June, September, October are the best months: clear days, cool nights, and lava that is hot enough to walk on but not punishing. July and August bring afternoon thunderstorms; hike early and watch the sky over Mount Taylor.
Winter closes some Forest Service roads to the Mount Taylor trailheads but leaves the lower-elevation lava country open and dramatically uncrowded. The Ice Cave is fine year-round — the temperature inside doesn't change.