Why are Mount Rainier and other high Cascade peaks covered by glaciers?

Mount Rainier and other high peaks in the Cascade Range are covered by glaciers primarily due to their high elevation and the region's maritime climate, which provides abundant moisture.12

The Pacific mountain system acts as an orographic barrier to storms arriving from the Pacific Ocean. As these moisture-laden air masses are forced upward by the mountains, they cool and release significant amounts of precipitation, much of which falls as snow on the higher western slopes.3

This high rate of annual snowfall allows glaciers to accumulate and persist even in temperate environments. Because these mountains are high, they maintain the cold temperatures necessary to sustain large ice fields, such as the extensive glacier system surrounding Mount Rainier. The steep gradient of net mass balance with altitude ensures that these peaks receive enough accumulation to support active glaciers, which serve as vital indicators of regional climate patterns.214