The Basal Temperature of Snow (BTS) method was used to predict permafrost distribution in two climatologically dissimilar mountain environments in northwest Canada. Permafrost probability maps with 30 m × 30 m grid cells were generated for part of the Ruby Range, Yukon Territory (425 km2), and for the Haines Summit area, northern British Columbia (536 km2), using winter BTS measurements in conjunction with late-summer ground truthing by probing and digging pits to physically verify the presence of permafrost. BTS values, and hence permafrost distribution, were modeled using elevation and potential incoming solar radiation (PISR) for the Ruby Range. PISR was not significant at Haines Summit, probably because persistent cloudiness associated with its more maritime climatic regime reduced aspect-induced variability in insolation. Probability maps indicate that ∼66% of the Ruby Range area and ∼43% of the Haines Summit area are underlain by permafrost. Therefore, the Ruby Range should be classified as extensive discontinuous permafrost, while Haines Summit is part of the sporadic discontinuous permafrost zone and not the isolated patches zone as portrayed on recent maps. Extensive ground truthing proved to be an essential part of the procedure because traditional BTS “rules-of-thumb” did not remain valid across the differing mountain climate zones.