Based on the Köppen climate classification, Mount Tilley is located in a subarctic climate zone with cold, snowy winters, and mild summers. Temperatures can drop below −20 °C with wind chill factors below −30 °C. Despite the modest elevation, the climate supports a small pocket glacier on the northeast face. Precipitation runoff from Mount Tilley drains north into Begbie Creek, a tributary of the Columbia River, or southwest into Wap Creek, a tributary of the Eagle River, which in turn is a tributary of the Fraser River.