Two Canadian cities on the same latitude have wildly different Januaries
Winnipeg and Vancouver both sit at 49 degrees north. Winnipeg's January days peak around minus 11 Celsius, with nights near minus 21. Vancouver, bathed by mild Pacific winds, stays above freezing on most January days. Latitude sets the stage for winter, but oceans, mountains and moisture write the script.
Winter is the coldest, darkest season in temperate and polar regions, arriving when a hemisphere tilts away from the Sun. Earth's axis leans about 23.44 degrees from its orbital plane, so the low winter Sun strikes the ground at a slant, spreading its energy thinly, and its light crosses more atmosphere, losing more heat on the way. Changes in Earth's distance from the Sun barely matter by comparison. The winter solstice brings the shortest day, though the earliest sunset and latest sunrise fall on different dates, thanks to the elliptical orbit.
Definitions vary. Meteorologists usually treat the three coldest months as winter: December to February in the north, June to August in the south. Sweden's weather institute calls it thermal winter once daily mean temperatures stay below zero for five consecutive days. Ancient Indo-European cultures seem to have split the year into just winter and summer, an idea that lingered in parts of Europe into the early Middle Ages alongside the newer four seasons.
Oceans soften the season. The British Isles, spanning roughly 49 to 61 degrees north, have no lowland weather station with an average January below freezing. The Southern Hemisphere has little land south of 40 degrees, so its winters are milder, with regular snow mostly confined to the Andes, New Zealand's mountains, Australia's Great Dividing Range and Patagonia, and year-round snow in Antarctica.
Cold brings its own oddities. Near minus 40 degrees, slightly moister air mixing with frigid surface air produces diamond dust, drifting hexagonal ice crystals. In Scandinavia, harsh winters come when high pressure settles in, which is why Stockholm's coldest January on record, in 1987, was also its sunniest. The English word itself descends from Proto-Germanic wintru, perhaps linked to an ancient root meaning water, though its origin remains uncertain.
Source: Winter
