Based on the Köppen climate classification, Mount Monica 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. Precipitation runoff from Mount Monica and meltwater from its surrounding glaciers drains west into Glacier Creek which is a tributary of the Duncan River, or east into Horsethief Creek, which is a tributary of the Columbia River.