The four seasons of the year in the United States - spring, summer, fall, and winter - are what determines weather, hours of daylight, and ecology throughout the year. In 2021, these are the astronomical dates and times for the start of each season:

  • Spring: March 20, at 5:37 A.M.
  • Summer: June 20, at 11:32 P.M.
  • Fall: September 22, at 3:21 P.M.
  • Winter: December 21, at 10:59 A.M.

The times correspond to the Eastern Time (ET) time zone and will vary in different states. 

Because the United States is located on the Northern Hemisphere of the planet, the rule of thumb is that the months of spring through to summer have the hottest temperatures, while the weather gets colder during fall and winter. 

However, this is a vast country with a few different regions, which means that there are three climatic zones in America. States such as California, Florida, Arizona, and Texas are usually warm all year round. On the other hand, places like New York, New England, Washington, and the Midwest have more distinct seasonal changes throughout the year. 

Spring

Spring starts on March 20 and lasts until June 20

The first day of spring happens on the spring equinox, which marks the astronomical beginning of spring. Meteorologically, spring begins on March 1st. 

This season comes after winter and before summer, is characterized by the temperatures warming and the days getting longer. It is during spring that plants start blossoming for the summer. 

What is the Spring Equinox?

Summer

Summer lasts from June 21 until September 22, which places it between spring and fall. 

This is the warmest of the months, where temperatures soar, and when there are more hours of daylight, as the days are longer than the evenings. In the United States, some regions have warm, humid weather, while in other areas the days are very hot and arid. 

The first day of summer is marked by the summer solstice, which corresponds to the astronomical beginning of summer.

Fall

Fall begins on September 22nd and ends on December 21st

During this season, temperatures start dropping, and the nights start getting longer again. Also known as autumn, in the United States fall gets its name because of the leaves on the trees that begin changing colors and falling. 

In some states, the landscape totally changes during fall, with greenery being replaced by bright reds and oranges. 

The autumnal equinox marks the first day of fall. 

Winter

Winter starts on December 21st, lasting through to March 20, falling right between fall and spring. 

In winter the weather gets colder, with some regions getting temperatures as low as 3 °F, and the nights become longer than the days. Many of the Northern states get snow throughout the season. 

The official beginning of winter falls on the winter solstice.

The Seasons of the Year Explained

The four seasons of the year shown around a globe.

There is an idea that summer is hotter than the other seasons because it happens when the Earth is closer to the sun, and that when the Earth is furthest from the sun, that's when winter occurs. This is false!

What controls the seasons is the Earth's axis, an imaginary pole that crosses the planet from top to bottom, on which the Earth spins, making one complete spin each day. 

This axis is tilted, and when the Earth orbits around the sun throughout the year, different parts of the planet receive the Sun's direct sunlight. This means that when the North Pole is tilted towards the Sun, it is summer in the Northern Hemisphere, and when it is tilted away from the sun, that's when it doesn't get as much light and heat, which causes winter and fall. 

Astronomical vs Meteorological First Days of the Seasons

Because most people observe the astronomical start of the seasons, not many know that there is also a meteorological beginning of the seasons. 

The difference is simple, the astronomical seasons go by the Earth's position in relation to the Sun, while meteorological seasons follow the temperature cycle. 

As an example, in 2021, the summer's astronomical start is June 20, but its meteorological start is June 1.

The Seasons in the Southern Hemisphere

The different seasons happen at different times in the Northern and Southern Hemispheres. So, when it is summer in the United States (Northern Hemisphere) it is winter in Australia (Southern Hemisphere).

These are the dates for the different seasons in the Southern Hemisphere in 2021:

  • Fall: Starts on March 20, and ends on June 20.
  • Winter: Begins on June 20, and lasts until September 22. 
  • Spring: Goes from September 22 until December 21. 
  • Summer: Starts on December 22, and lasts until March 21.