The Simien Mountains are best visited in the dry season, which runs from October to May. The core trekking season is October to early December and February to May. During these periods the weather is generally clear, the tracks are dry, and views from the escarpment are at their best. January can bring cold spells and occasional frost at the higher camps; the days remain clear and bright.
The rainy season (June–September) makes trekking difficult — the paths become muddy, leeches appear, and cloud obscures the escarpment views for days at a time. Some operators offer treks in the shoulder months (September, June) with reduced prices and fewer other trekkers; the weather is unreliable but not impossible. The geladas are present year-round. The Ethiopian wolf is more visible in the dry season when vegetation is shorter and the animals are easier to spot hunting in the open moorland.
Temperatures at the higher camps drop below freezing at night even in the dry season; a warm sleeping bag rated to -5°C or colder is essential. Days at altitude are typically warm and sunny until afternoon cloud builds from below the escarpment.