Lasionycta promulsa is a moth of the Noctuidae family. It occurs from Rampart House in northern Yukon to south-western British Columbia in the west and southern New Mexico in the Rocky Mountains. It is most common near timberline and is nocturnal. The northern Yukon populations are found in sage grassland, although those on Montana Mountain in southwest Yukon occur in rocky alpine tundra like other populations to the south. Adults are on wing from mid-July through August.