Tuesday March 19th at 11:06 pm is the Vernal Equinox, the advent of the first day of astronomical SPRING. It certainly seems to have been a long time coming but you can count on it every year on either March 19th, 20th, or 21st.
In the Northern Hemisphere, the Spring or vernal equinox occurs when the Sun crosses the equator line, heading north. This event marks the start of the spring season in the northern half of the globe. After this date, the Northern Hemisphere begins to be tilted more toward the Sun, resulting in increasing daylight hours and warming temperatures.
In the Southern Hemisphere, it’s the opposite: the March equinox marks the start of Autumn, as the Southern Hemisphere begins to be tilted away from the Sun.
The astronomical start date of the seasons is based on the position of the Sun in relation to the Earth:
- Spring runs from March 19 to June 21
- Summer runs from June 20 to September 21
- Fall (Autumn) runs from September 22 to November 30
- Winter runs from December 1 to February 28 (February 29 in a leap year)
The meteorological determination of Spring is different. The 12 months of the year are divided equally into 4 seasons of 3 months each, and the seasons begin on the first day of the months, including the equinoxes (Spring and Fall) and solstices (Winter and Summer). In the Northern Hemisphere, for example:
- Spring runs from March 1 to May 31
- Summer runs from June 1 to August 31
- Fall (Autumn) runs from September 1 to November 30
- Winter runs from December 1 to February 28 (February 29 in a leap year)
Although the vernal equinox on March 19 is typically observed as the first day of spring, meteorological spring starts on March 1.
After a mild winter in many parts of the country, spring should arrive early. A look ahead at the latest forecast suggests that we will see an unusually warm spring in Virginia and Washington, D.C.
For several weeks in March, if someone asks you which season we are in, you may have to clarify whether they are asking for the astronomical or meteorological definition before you can answer correctly.