Continental climates often have a significant annual variation in temperature (warm summers and cold winters). They tend to occur in the middle latitudes (40 to 55 north), within large landmasses where prevailing winds blow overland bringing some precipitation, and temperatures are not moderated by oceans. Continental climates occur mostly in the Northern Hemisphere due to the large landmasses found there. Most of northern and northeastern China, eastern and southeastern Europe, Western and north western Iran, central and southeastern Canada, and the central and northeastern United States have this type of climate. Continentality is a measure of the degree to which a region experiences this type of climate. In continental climates, precipitation tends to be moderate in amount, concentrated mostly in the warmer months. Only a few areas—in the mountains of the Pacific Northwest of North America and in Iran, northern Iraq, adjacent Turkey, Afghanistan, Pakistan, and Central Asia—show a winter maximum in precipitation. A portion of the annual precipitation falls as snowfall, and snow often remains on the ground for more than a month. Summers in continental climates can feature thunderstorms and frequent hot temperatures; however, summer weather is somewhat more stable than winter weather. In Köppen climate classification it is identified with the letter D. Seasons Annual precipitation in this zone is usually between and , The timing of intermediate spring-like or autumn-like temperatures in this zone vary depending on latitude and/or elevation. For example, spring may arrive as soon as March in the southern parts of this zone or as late as May in the north. Summers are warm or hot while winters are below freezing and sustain frost. Köppen climate classification Most such areas fit Köppen climate classifications of Dfa having hot summers (mean temperature above 22 °C/71.6 °F) or Dfb with warm summers (mean temperature below 22 °C/71.6 °F). Dry-summer continental climates (Dsa and Dsb) exist in high altitude areas near Mediterranean climates (Csa/Csb). Dry-winter continental climates (Dwa and Dwb) exist in high altitude areas near humid subtropical climates (Cwa) or subtropical highland climates (Cwb). In some cases, the semi-arid climate classification of BSk and the arid climate of BWk can also be considered to be continental as long as it has cold winters, though it isn't by the Köppen classification. The definition of this climate regarding temperature is as follows: the mean temperature of the coldest month must be below -3 C (26.6 F) and