Why does it rain a lot in spring? The arrival of spring heralds a time of renewal, increased warmth, and plentiful precipitation.
People often wonder why it rains so much in the spring, despite the fact that it may be a welcome relief from the colder months of winter.
However, excessive rain can also cause all sorts of problems, which is why you have to be prepared.
But, again, why does it rain so much in spring?
It may rain a lot in spring because of the altering weather patterns, Earth’s axial tilt, topography, and atmospheric variables.
Why Does It Rain a Lot in Spring?
In spring, the days grow longer and temperatures increase. It marks the transition between winter and summer.
But you will also witness heavy rain in the season, and it could be due to many factors:
- Frontal Systems
- Low Pressure Systems
- Global Climate Effects
Fact: For meteorologists Spring starts in March and ends in June. For astronomers, spring in the northern hemisphere begins around the 20th of March on the day of the vernal equinox.
As temperatures rise, they can trigger sudden and sometimes dramatic weather changes signaled by the arrival of frontal weather systems.
This is where warm air and cold air masses meet.
A stationary front is too dense with moisture to move, but three other frontal systems move air around, and they all contribute to rain formation in spring.
The Impact of Cold Fronts
All weather fronts are transitional areas at the edges of the air masses.
A cold front is the boundary of a cold air mass.
It moves fast, pushing warmer air masses out of the way creating turbulence and producing clouds to announce a dramatic change in the weather.
The temperature suddenly falls as the warm air is pushed up into the troposphere to produce cumulus or cumulonimbus clouds typical of thunderstorms.
These can also form hail.
The Impact of Warm Fronts
Warm fronts form when an advancing warm air mass pushes into a cold air mass.
These fronts have a low air density and move slower than cold fronts because they push against cold heavy air.
They often bring stormy weather with high cirrus or cirrostratus clouds forming ahead of the front as the warm air mass rises above the cool.
When the front passes over an area, the clouds lower making rain more likely.
Fact: Lake-effect happens wherever the difference in the temperature of the air and water’s surface is more than 50oF, which may produce precipitation on the leeward side of the water.
The Impact of Occluded Fronts
An occluded front is where a fast-moving cold air mass catches up with a slow-moving warm front.
The lighter warm air is forced up and out of the way.
They usually form around areas of low atmospheric pressure producing cumulonimbus or nimbostratus clouds and precipitation.
As the cold air meets the cool air ahead of the warm front, the wind changes direction.
Temperatures rise or fall but once the front passes conditions settle.
Ascending and descending air create areas of high and low pressure.
As air warms and ascends, low pressure at the earth’s surface develops, a depression.
Although the low-pressure levels vary throughout the system, pressures are lowest at the center of the system.
This draws air forcing the system to rotate, anticlockwise in the northern hemisphere, in an attempt to equalize the pressures.
At times of low pressure, the weather is typically windy with unsettled conditions.
Low-Pressure System and Its Relationship with Rainfall
Air pressure is the weight of air or its density, which varies according to how much water vapor it supports.
It is easier for air to rise when the air pressure is low and warm air rises very high where the vapor condenses as clouds.
The higher the cloud the greater the potential for rain and thunderstorms.
Warm air can be pulled up and over the cool resulting in extended periods of precipitation, including snow.
Storms develop in late spring and summer with thick dense clouds that are heavy with rain and sometimes hail.
The violence with which the warm moist air rises creates strong gusty winds, thunder and lightning and the characteristic towering cumulonimbus cloud.
Eventually, the vapor precipitates out, often in torrential downpours.
Rainfall Associated with Thunderstorms
Because they are regulated by temperature, thunderstorms are typically localized phenomena that produce heavy precipitation when warm.
They form as powerful updrafts carry wet air warmed by the surface violently upwards into the cold of the atmosphere where water vapor condenses out.
The thinner high layers of the atmosphere cannot support the weight of the droplet and it falls as rain, sometimes freezing to hail as it passes through colder layers to the ground.
The topography and terrain of any area impact how the air around it heats up, cools down and moves about.
High elevations tend to be cooler, particularly in spring.
At night, the cold air descends and pools in valleys to be subjected to lifting on its windward side resulting in rain.
Fact: Rising surface temperatures take longer to impact temperatures higher up.
Mountain Ranges Effects on Spring Rain
Temperatures typically decrease by 4 or 5oF per thousand feet even when the valleys are at a more constant temperature.
The air loses moisture as it hits the windward side of mountains, leaving a rain shadow on the leeward.
However, in spring, cold fronts can bring shallow cold dense air into the lower elevations with lifted air getting more precipitation throughout the year, but especially in spring.
Fact: Our oceans impact the climate and drive global weather but all large bodies of water absorb heat although not as efficiently as the ground.
Global Climate Factors
All current research predicts a warmer wetter global climate.
Our winters are already shorter and there is water locked away as ice or snow and more readily available for evaporation.
Water vapor is a major greenhouse gas, so the expectation is there will be hot humid weather much earlier in spring.
El Niño and La Niña Events
ENSO, El Nino Southern Oscillation is a 2 to 7-year cycle of warm and cool episodes in the Pacific Ocean.
It is the largest driver of seasonal global weather variation impacting energy production and agriculture, freshwater supplies, public health and economic activity around the globe.
Impact on Global Weather Patterns
La Niña and El Niño weather patterns periodically interrupt the trade winds that blow west across the Pacific towards Asia.
El Niño is characterized by weakening trade winds and warm water being pushed back east towards the west coast of the Americas.
La Niña is a cold weather event that pushes more than usual water towards Asia.
During a La Niña year, in the south winter temperatures are warmer than typical and, in the north, cooler.
Effects on Spring Rainfall
ENSO upsets how heat and energy are usually distributed.
In a La Niña the trade winds blow harder distributing more energy poleward disturbing the jet stream.
This results in less spring rain in the southern U.S. and heavy rain in the Pacific Northwest and Canada.
In El Niño, concentrated heat at its center redirects seasonal storms resulting in drought across India, Indonesia and Australia and a large part of the Amazon.
Climate Change Issues
It is not just fears that the ENSO events will increase in frequency, climate change is expected to increase in severity.
Storms winds will increase, rainfall will be more frequent and intense as the warmer atmosphere takes in more water.
In general, we must be prepared for extremes in our weather.
It is not totally clear how the rainfall in the mid-latitudes will be impacted by stronger El Niños and La Niñas.
Rainfall extremes will, in all likelihood, shift east along the equator during extreme El Niño events and westward during the La Niñas.
Spring rains will fall harder for longer even inland if there is water, but not everywhere.
As the jet streams shift, huge regions of the globe can expect long term drought.
Fact: In rising spring temperatures, more heat is absorbed over water, increasing the evaporation rate and the chance of rain.
Why does it rain a lot in spring?
An increase in precipitation is frequently associated with the approach of spring, and this can have both positive and negative results.
Frontal systems, low-pressure systems, thunderstorms, topography, and global climate impacts like El Nio and La Nia all play a role in bringing about spring rain.