Spring is the season after winter and before summer. Days become longer and weather gets warmer in the temperate zone because the Earth tilts towards the Sun. In many parts of the world plants grow and flowers bloom. Often people with hay fever suffer more, because of the allergens. Many animals have their breeding seasons in spring. In many parts of the world it rains for hours. This helps the plants grow and the flowers bloom. At the start of spring, people suffering from seasonal affective disorder will feel better. Hay fever, however, often becomes worse.
During early spring, the axis of the Earth is increasing its tilt relative to the Sun, and the length of daylight rapidly increases for the relevant hemisphere. The hemisphere begins to warm significantly, causing new plant growth to "spring forth," giving the season its name.
Many flowering plants bloom at this time of year, in a long succession, sometimes beginning when snow is still on the ground and continuing into early summer. In normally snowless areas, "spring" may begin as early as February (Northern Hemisphere), heralded by the blooming of deciduous magnolias, cherries, and quince, or August (Southern Hemisphere) in the same way. Many temperate areas have a dry spring, and wet autumn (fall), which brings about flowering in this season, more consistent with the need for water, as well as warmth. Subarctic areas may not experience "spring" at all until May.
While spring is a result of the warmth caused by the changing orientation of the Earth's axis relative to the Sun, the weather in many parts of the world is affected by other, less predictable events. The rainfall in spring (or any season) follows trends more related to longer cycles—such as the solar cycle—or events created by ocean currents and ocean temperatures—for example, the El Niño effect and the Southern Oscillation Index.
Unstable spring weather may occur more often when warm air begins to invade from lower latitudes, while cold air is still pushing from the Polar regions. Flooding is also most common in and near mountainous areas during this time of year, because of snow-melt which is accelerated by warm rains. In North America, Tornado Alley is most active at this time of year, especially since the Rocky Mountains prevent the surging hot and cold air masses from spreading eastward, and instead force them into direct conflict. Besides tornadoes, supercell thunderstorms can also produce dangerously large hail and very high winds, for which a severe thunderstorm warning or tornado warning is usually issued. Even more so than in winter, the jet streams play an important role in unstable and severe Northern Hemisphere weather in springtime.
In recent decades, season creep has been observed, which means that many phenological signs of spring are occurring earlier in many regions by around two days per decade.
Spring in the Southern Hemisphere is different in several significant ways to that of the Northern Hemisphere for several reasons, including:
- there is no land bridge between Southern Hemisphere countries and the Antarctic zone capable of bringing in cold air without the temperature-mitigating effects of extensive tracts of water;
- the vastly greater amount of ocean in the Southern Hemisphere at all latitudes;
- at this time in Earth's geologic history the Earth has an orbit which brings it in closer to the Southern Hemisphere for its warmer seasons;
- there is a circumpolar flow of air (the roaring 40s and 50s) uninterrupted by large land masses;
- no equivalent jet streams; and
- the peculiarities of the reversing ocean currents in the Pacific.
Spring Facts for Kids. Kiddle Encyclopedia.