Sweden's spring starts only after seven straight days averaging above freezing
When does spring begin? In Sweden, meteorologists wait until the daily average temperature stays above zero for seven days in a row, so the date can land anywhere from mid-February to the end of July depending on where you live. Ask a Persian, a Chinese or an Irish calendar and you get different answers again.
Meteorologists in most temperate places simply split the year into four three-month blocks by temperature, which puts spring in March, April and May in the United States and Britain, and in September, October and November in Australia, South Africa and Brazil. Astronomers prefer the vernal equinox, between 19 and 21 March in the north, when day and night are each about twelve hours. Older traditions start earlier. Ireland's calendar counts February to April. The Chinese season runs from Lichun in early February to Lixia in early May, and Celtic reckoning likewise stretched from around Imbolc to Beltane, with Saint Patrick's Day on 17 March as its midpoint. The Roman scholar Varro dated spring from 7 February to 8 May, while the Persian year opens with the first day of Farvardin on 20 or 21 March.
Nature keeps its own calendar. Ecologists track blossoming plants, animal activity and even the distinctive smell of soil once it warms enough for microbes to thrive. Some divide the year into six seasons, adding a prevernal stretch when only tough flowers such as crocuses bloom, sometimes through lingering snow. In recent decades these signs have been arriving earlier, by about two days per decade in many regions.
The word itself comes from phrases like springing time, recorded in the 14th century, built on an Old English verb meaning to rise or burst forth that was not originally tied to the season. The physics matches: as a hemisphere tilts toward the Sun, days lengthen fast, snow melts and swells rivers, and growth surges.
Spring can also be violent. Warm air pushing in from lower latitudes collides with lingering polar air, and in North America the Rocky Mountains funnel those masses into direct conflict, making Tornado Alley most active now. Snowmelt sped up by warm rain makes mountain flooding most common in this season. The Southern Hemisphere's spring behaves differently, shaped by its vast oceans and the uninterrupted westerly winds of the roaring forties and fifties.
Source: Spring (season)
