This article was originally published on March 30, 2021.
“April showers bring May flowers,” or so we’ve been told. Perhaps that is why every year in the Northern Hemisphere, the arrival of spring brings predictably rainy months.
However, it is important to note that spring does not occur at the same time all over the world. The changing of the seasons is a result of the Earth’s rotation around the sun, so the timing of a a given season depends on which hemisphere you are in. In the Northern Hemisphere, each season lasts about three months, with spring extending between March 1 and May 31. The Southern Hemisphere experiences the opposite seasons, with spring falling between September 1 and November 30.
In general, the Northern Hemisphere receives more precipitation than its southern counterpart. But what exactly causes spring rain in areas north of the equator?
Spring Rain: Transition to Summer
Whether a region is particularly rainy depends on where you live: Factors such as latitude, altitude, prevailing winds and topography play a role precipitation. This combination of ingredients positions the Northern Hemisphere to receive rain, especially in the spring in USA.
As it turns out, the mystery behind seasonal precipitation—in this case, rain in the spring—is actually relatively simple. The clouds above us are formed from water vapor that has evaporated from the Earth’s surface. During the spring transition from lower to higher temperatures, the air around us heats up. The cool, dry winter air combines with a warm, humid oncoming summer air. The combination of temperatures causes this air to rise and moisture to escape as rain.
Read more: How to build your own rain garden and why you should
This results in a particularly wet spring in the Northern Hemisphere due to a combination of ideal temperature conditions, proximity to mountain ranges and prevailing winds.
And when summer finally approachesspring showers change to occasional showers as temperatures rise.
Spring in the Southern Hemisphere
While it’s raining the southern hemisphere in their springshowers don’t happen everywhere.
According to Trenberth, the configuration of the continents relative to the ocean is quite different south of the equator: the continents are subtropical and the main storm tracks are at higher latitudes than in the northern hemisphere, meaning that areas such as New Zealand, Tasmania and South Australia, South Africa and southern Chile and Argentina experience the most spring storms.
April showers bring tornadoes and thunderstorms?
Kevin Trenberth, a climate scientist who directs the climate analysis section at the National Center for Atmospheric Research (NCAR)explains that spring brings numerous thunderstorms and tornadoes.
In the US, the storms are moving from the Pacific Ocean to the eastern region while picking up a lot of moisture from the Gulf of Mexico. This can often lead to massive thunderstorms and tornado outbreaks.
Opposing climate patterns in the Pacific known as El Niño and La Niña can also affect weather conditions worldwide. El Niño occurs when surface waters are warmer than usual around the Pacific equator. In contrast, Trenberth describes La Niña, when conditions are colder than normal in the tropical Pacific but warmer near Indonesia. In fact, forecasts this year call for a more vigorous tornado season than usual because of the La Niña pattern, he says.
A future of changing seasons: More spring rain?
Global warming caused by climate change provokes change of seasons around the world. With shorter winters and relatively earlier springs, rising temperatures are also upsetting weather patterns: As the world warms, more water evaporates, leading to more moisture in the atmosphere over the oceans.
This causes more intense rain and can cause more storms and increase the risk of spring flooding. Conversely, milder months may bring less rain in the future – anything it depends where you live.