Surprisingly, Sapporo, at around 43°N, is about the same latitude as Marseille in the south of France and southern Oregon in the USA. The freezing winters for which Hokkaidō are known are a result of the island's proximity to Siberia and cold northwesterly winds, which bring significant snowfall, especially on the Sea of Japan side of the island.
Summers in Hokkaidō are relatively cool and dry compared to hot and humid Honshū to the south (making the island a popular escape). The typhoons that can wreck travel plans in the southern half of Japan don't usually reach this far – though one did, in 2016, causing enough damage to suspend some rail lines for months. Winter comes early: Daisetsuzan gets its first snowfall in October (and sometimes late September). This range of mountains in the dead centre of Hokkaidō is the coldest region in Japan, where temperatures can drop to -20°C.
Dangers & Annoyances
Wildlife and weather pose the biggest threats in Hokkaidō. Hikers need to be wary of bears and foxes. It's estimated that 40% of Hokkaidō's foxes carry the parasitic worm echinococcus, so keep away from them and boil your water if camping. If you're driving, keep an eye out for deer, especially at night, and inquire about road conditions if you're heading up into the mountains outside of the summer season.
Warning: Bear Activity
Hokkaidō is bear country. The bears up here are different to the small black bears that inhabit Honshū; these are higuma (Ussuri brown bear), thought to be the ancestor of the North American grizzly bear, and they're much bigger and more aggressive.
Take all precautions, especially in the early morning and at dusk, and avoid hoofing it alone. Make a lot of noise; like Japanese hikers, tie a kuma-yoke (bear bell) to your rucksack. The theory goes that bears want to meet you face to face about as much as you want to meet them face to face and if they hear you coming, they'll avoid you at all costs.
If you're camping, use the steel food bins or tie up your food and do not bury your rubbish. Bear activity picks up noticeably during early autumn when the creatures are actively foraging for food ahead of their winter hibernation. Be especially cautious at this time.
The Shiretoko peninsula is home to the highest concentration of higuma on Hokkaidō, but they are also often sighted in Daisetsuzan National Park; really, they could be anywhere there are mountains. Only the remote islands of Rishiri-tō and Rebun-tō are bear-free.