A humid continental climate is a climatic region defined by Russo-German climatologist Wladimir Köppen in 1900,^[1] typified by four distinct seasons and large seasonal temperature differences, with warm to hot (and often humid) summers, and cold (sometimes severely cold in the northern areas) and snowy winters. Precipitation is usually distributed throughout the year, but often these regions do have dry seasons. The definition of this climate in terms of temperature is as follows: the mean temperature of the coldest month must be below 0 °C (32.0 °F) or −3 °C (26.6 °F) depending on the isotherm,^[2] and there must be at least four months whose mean temperatures are at or above 10 °C (50 °F). In addition, the location in question must not be semi-arid or arid. The cooler Dfb, Dwb, and Dsb subtypes are also known as hemiboreal climates. Although amount of snowfall is not a factor used in defining the humid continental climate, snow during the winter in this type of climate is almost a guarantee, either intermittently throughout the winter months near the poleward or coastal margins, or persistently throughout the winter months elsewhere in the climate zone.

Humid continental climates are generally found between latitudes 40° N and 60° N,^[3] within the central and northeastern portions of North America, Europe, and Asia. Occasionally, they can also be found at higher elevations above other more temperate climate types. They are rare in the Southern Hemisphere, limited to isolated high altitude locations, due to the larger ocean area at that latitude, smaller land mass, and the consequent greater maritime moderation.

In the Northern Hemisphere, some of the humid continental climates, typically in Hokkaido, Sakhalin Island, northeastern mainland Europe, Scandinavia, Nova Scotia, and Newfoundland are closer to the sea and heavily maritime-influenced and comparable to oceanic climates, with relatively cool summers, significant year-round precipitation (including high amounts of snow) and winters being just below the freezing mark (too cold for such a classification).^[4] More extreme and inland humid continental climates, sometimes known as "hyper-continental" climates, are found in northeast China, southern Siberia, Mongolia, Kazakhstan, most of the southern interior of Canada, and the Upper Midwest, where temperatures in the winter resemble those of adjacent subarctic climates (with long, drier, generally very cold winters) but have longer and generally warmer summers (in occasional cases, hot summers). A more moderate variety, found in places like Northern Honshu, east-central China, the Korean Peninsula, parts of Eastern Europe, parts of southern Ontario, much of the American Midwest, and the Northeast US, the climate combines hotter summer maxima and greater humidity (similar to those found in adjacent humid subtropical climates) and moderately cold winters and more intermittent snow cover (averaging somewhat below freezing, too cold for a more temperate classification), and is less extreme than the most inland hyper-continental variety.

Definition

Using the Köppen climate classification, a climate is classified as humid continental when the temperature of the coldest month is below 0 °C or −3 °C and there must be at least four months whose mean temperatures are at or above 10 °C (50 °F).^[5] These temperatures were not arbitrary. In Europe, the −3 °C (27 °F) average temperature isotherm (line of equal temperature) was near the southern extent of winter snowpack. In the United States, it is more common to use the 0 °C isotherm instead. The 10 °C (50 °F) average temperature was found to be roughly the minimum temperature necessary for tree reproduction and growth.^[6] Wide temperature ranges are common within this climate zone.^[7]

Second letter in the classification symbol defines seasonal rainfall as follows:^[5]

• s: A dry summer—the driest month in the high-sun half of the year (April to September in the Northern Hemisphere, October to March in the Southern Hemisphere) has less than 30 millimetres (1.18 in)/40 millimetres (1.57 in) of rainfall and has exactly or less than 1⁄3 the precipitation of the wettest month in the low-sun half of the year (October to March in the Northern Hemisphere, April to September in the Southern Hemisphere).
• w: A dry winter—the driest month in the low-sun half of the year has exactly or less than one‑tenth of the precipitation found in the wettest month in the summer half of the year.
• f: No dry season—does not meet either of the alternative specifications above; precipitation and humidity are often high year-round.

while the third letter denotes the extent of summer heat:^[5]

• a: Hot summer, warmest month averages at least 22 °C (71.6 °F),
• b: Warm summer, warmest month averages below 22 °C (71.6 °F) but at least four months averages above 10 °C (50.0 °F).

Associated precipitation

Within North America, moisture within this climate regime is supplied by the Great Lakes, Gulf of Mexico and adjacent western subtropical Atlantic.^[8] Precipitation is relatively well distributed year-round in many areas with this climate (f), while others may see a marked reduction in wintry precipitation,^[6] which increases the chances of a wintertime drought (w).^[9] Snowfall occurs in all areas with a humid continental climate and in many such places is more common than rain during the height of winter. In places with sufficient wintertime precipitation, the snow cover is often deep. Most summer rainfall occurs during thunderstorms,^[6] and in North America and Asia an occasional tropical cyclone (or the remnants thereof). Though humidity levels are often high in locations with humid continental climates, the "humid" designation means that the climate is not dry enough to be classified as semi-arid or arid.

Vegetation

By definition, forests thrive within this climate. Biomes within this climate regime include temperate woodlands, temperate grasslands, temperate deciduous or evergreen forests,^[8] coniferous forests, and coniferous swamps.^[10] Within wetter areas, maple, spruce, pine, fir, and oak can be found. Fall foliage is noted during the autumn of deciduous forests.^[6]

Hot summer subtype

A hot summer version of a continental climate features an average temperature of at least 22 °C (71.6 °F) in its warmest month.^[11] Since these regimes are restricted to the Northern Hemisphere, the warmest month is usually July or August. High temperatures in the warmest month tend to be in the high 20s or low 30s °C (80s or low 90s °F), while average January afternoon temperatures are near or well below freezing. Frost-free periods normally last 4–7 months within this climate regime.^[6]

Within North America, this climate includes portions of the central and eastern United States from east of 100°W to south of about the 44°N to the Atlantic. Precipitation increases further eastward in this zone and is less seasonally uniform in the west. The western states of the western United States (namely Montana, Wyoming, parts of southern Idaho, most of Lincoln County in Eastern Washington, parts of Colorado, parts of Utah, isolated parts of northern New Mexico, western Nebraska, and parts of western North and South Dakota) have thermal regimes which fit the Dfa climate type, but are quite dry, and are generally grouped with the steppe (BSk) climates. In the eastern and Midwestern United States, Pennsylvania, Ohio, Illinois, Indiana, southern New York, southern Connecticut, and southern Rhode Island fall into the hot-summer humid continental climate. In Canada, this climate type exists only over portions of Southern Ontario.

In the Eastern Hemisphere, this climate regime is found within interior Eurasia and east-central Asia. Within Europe, the Dfa climate type is present near the Black Sea in southern Ukraine, the Southern Federal District of Russia, southern Moldova, Serbia, parts of southern Romania, and Bulgaria,^[14][15] but tends to be drier and can be even semi-arid in these places. In East Asia, this climate exhibits a monsoonal tendency with much higher precipitation in summer than in winter, and due to the effects of the strong Siberian High much colder winter temperatures than similar latitudes around the world, however with lower snowfall, the exception being western Japan with its heavy snowfall. Tōhoku, between Tokyo and Hokkaidō and Western coast of Japan also has a climate with Köppen classification Dfa, but is wetter even than that part of North America with this climate type. A variant which has dry winters and hence relatively lower snowfall with monsoonal type summer rainfall is to be found in northern China including Manchuria and parts of North China, south-east Russia, and over much of the Korean Peninsula; it has the Köppen classification Dwa. Much of central Asia, northwestern China, and southern Mongolia has a thermal regime similar to that of the Dfa climate type, but these regions receive so little precipitation that they are more often classified as steppes (BSk) or deserts (BWk).

Dsa climates are rare; they are generally restricted to elevated areas adjacent to mid-latitude Mediterranean climate regions with a Csa climate well inland to ensure hot summers and cold winters. They are generally found in the highly elevated areas of south-eastern Turkey (Hakkâri), north-western Iran, northern Iraq, parts of Central Asia, parts of the High Atlas mountain range in central Morocco and very small parts of the Intermountain West in the United States.

This climate zone does not exist at all in the Southern Hemisphere, where the continents either do not penetrate low enough in latitude or taper too much to have any place that gets the combination of snowy winters and hot summers. Marine influences are very strong around 40°S and such preclude Dfa, Dwa, and Dsa climates in the southern hemisphere.

Warm summer subtype