When you are stuck inside on a rainy, mid-April day, you may hear someone tell you “April showers bring May flowers,” but is there any truth to this proverb? Originating from Geoffrey Chaucer’s The Canterbury Tales, the words were adapted a century later by Thomas Tusser into “Sweet April showers do spring May flowers.” However, it seems like these writers may never have researched why exactly April showers exist. In reality, April showers exist because of a natural phenomenon called jet streams.
Jet streams are wave-like air currents that form in the lowest layer of the atmosphere, the tropopause, and flow west to east between 5.6 to 9.9 miles above sea level. There are two types of jet streams: polar jets and subtropical jets. Polar jets flow between 5.6 to 7.5 miles above sea level while subtropical jets flow between 6.2 to 9.9 miles above sea level. Furthermore, polar jets are stronger because they are lower, and subtropical jets are weaker because they are higher. They carry water vapor, and varying temperatures of air, as well as weather events like cyclones. Jet streams are also very unpredictable and can cause damage to unsuspecting people. For example, in 2007 polar jets stayed south, causing Cyclone Uriah to hit the United Kingdom leading to €6.5 billion in damages and 13 deaths. This unpredictability is what causes spring to constantly have jumps in weather from beautiful sunny days to cold, wet, and windy ones.
The El Niño-Southern Oscillation also plays a role in the rainy season. It changes the direction of polar jet streams, causing weather to become more rainy in some places and drier in others. Overall, a simple expression used to express a change from hardship to calmness takes roots in weather conditions that can still be seen today around the world.
If you are interested in tracking the rainfall or jet streams with shocking accuracy, check out:
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