Humidity and increased amount precipitation augmented by fog or cloud. Sub-canopy composed of small shrubs. Frost can occur, freezing temperatures on volcanic peaks in Mexico and Central America and the upper reaches of the Sierra Madre Occidental and Sierra Madre Oriental. Understory much more tropical. Temperature cool but not freezing.
Constant cloud cover rather than periodic fog.
Cool temperatures, frost common. Can be at low elevations in North America and probably formed by strong on-shore winds. Defined by a timberline in South America. Top of volcanic peaks in Latin America and in the Andes. Freezing temperatures possible every month.