Whitebark pine (Pinus albicaulis), an endangered keystone alpine tree species, faces multiple threats across its western North American range. Little is known of whitebark pine in the southern Coast Mountains of British Columbia relative to well-studied Rocky Mountain populations, especially with regard to the effects of climate on annual radial growth. Our results indicate centenarian whitebark pine annual radial growth is negatively influenced by the onset of snowfall in the prior autumn. This unusual growth limitation likely stems from the truncation of the prior year growing season and reduced physiological preparedness for growth in the following year. Autumn snowfall is moderated by temperature and the Pacific Decadal Oscillation (PDO), which controls largescale weather patterns in the study region. Our results are distinct from studies of mature whitebark pine trees in continental populations where growth is typically limited by summer temperature, or occasionally by winter snowfall due to a reliance on snow meltwater during spring/summer. We suggest that predicted warmer and wetter climate and reduced snowpacks in the southern Coast Mountains may benefit the growth of the young population of maritime whitebark pine over the next few decades.