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Climate

As Japan's coldest region, Hokkaidō has relatively cool summers and icy/snowy winters. Most of the island falls in the humid continental climate zone with Köppen climate classification Dfb (hemiboreal) in most areas but Dfa (hot summer humid continental) in some inland lowlands. The average August temperature ranges from 17 to 22 °C (62.6 to 71.6 °F), while the average January temperature ranges from −12 to −4 °C (10.4 to 24.8 °F), in both cases depending on elevation and distance from the ocean, though temperatures on the western side of the island tend to be a little warmer than on the eastern. The highest temperature ever recorded is 39.5 °C (103.1 °F) on 26 May 2019.

The northern portion of Hokkaidō falls into the taiga biome with significant snowfall. Snowfall varies widely from as much as 11 metres (400 in) on the mountains adjacent to the Sea of Japan down to around 1.8 metres (71 in) on the Pacific coast. The island tends to have isolated snowstorms that develop long-lasting snowbanks. Total precipitation varies from 1,600 millimetres (63 in) on the mountains of the Sea of Japan coast to around 800 millimetres (31 in) (the lowest in Japan) on the Sea of Okhotsk coast and interior lowlands and up to around 1,100 millimetres (43 in) on the Pacific side. The generally high quality of powder snow and numerous mountains in Hokkaidō make it a popular region for snow sports. The snowfall usually commences in earnest in November and ski resorts (such as those at Niseko, Furano, Teine and Rusutsu) usually operate between December and April. Hokkaidō celebrates its winter weather at the Sapporo Snow Festival.

During the winter, passage through the Sea of Okhotsk is often complicated by large floes of drift ice. Combined with high winds that occur during winter, this frequently brings air travel and maritime activity to a halt beyond the northern coast of Hokkaidō. Ports on the open Pacific Ocean and Sea of Japan are generally ice-free year round, though most rivers freeze during the winter.

Unlike the other major islands of Japan, Hokkaidō is normally not affected by the June–July rainy season and the relative lack of humidity and typically warm, rather than hot, summer weather makes its climate an attraction for tourists from other parts of Japan.