In climatology, the term mesothermal is used to refer to certain forms of climate found typically in the Earth's temperate zones. It has a moderate span of temperature, with winters not cold enough to sustain snow cover. Summers are warm within oceanic climate regimes, and hot within continental or subtropical climate regimes. Origin of term The term is derived from two Greek words meaning "having a moderate amount of heat." This can be misinterpreted, however, since the term is actually intended to describe only the temperature conditions that prevail during the winter months, rather than those for the year as a whole. Definition Under the original Köppen climate classification, all places with an average temperature in their coldest month that is colder than 18°C, but warmer than −3°C, are said to have a mesothermal climate. The isotherm of -3°C for the coldest monthly mean temperature, was observed to be the line where the climate was likely cold enough to support a fixed period of continuous snow cover every year. In some climate classifications the isotherm of 0°C (32°F) for the coldest monthly mean temperature is observed as the line between mesothermal climates and microthermal climates where the coldest month has a mean temperature below -3°C. Range In the US, the northern boundary line between mesothermal and microthermal ranges is north of Juneau and Sitka along the margins of the Pacific Ocean. It then goes southeastward around about 42N latitude across the north-central US (not including mountain regions) then eastward across the lower Midwest to the East Coast near Boston. The southern boundary line between mesothermal and megathermal (or tropical) is across south Florida just above Palm Beach. Summer variants Summers in mesothermal climates may be hot (having an average temperature in their warmest month of 22 °C or above) or mild (with the warmest month averaging between 10 °C and 18 °C). The hot-summer, or subtropical mesothermal climate is encountered near the tropics of both hemispheres, in the landmass interiors of Asia and North America and along their east coasts, while the cool to mild summer climate is found along upper west coast and where oceanic climates are found. List of mesothermal cities and their summer temperatures: Hong Kong-hot summer Los Angeles- hot summer Milan-hot summer New York City-hot summer Tokyo-hot summer London-warm summer Mexico City-warm summer Vancouver-warm summer Moisture In addition to being subdivisible by summer temperature, mesothermal climates