March 1st every year is the first day of Meteorological Spring. Astronomical Spring begins later in the month.
Meteorological Spring is based on the annual temperature cycle, while Astronomical Spring is defined based on the vernal solstice.
As we leave our cold season and milder conditions approach, we define spring in terms of weather simply as the start of March. Meteorological Spring lasts until the last day of May. June 1st is the beginning of Meteorological Summer.
In terms of Earth’s position relative to the sun, Astronomical Spring is determined. This is the Vernal Equinox. Here the Earth’s axis is neither titled away or towards the sun. This allows for nearly equal amounts of daylight and darkness at all latitudes.
Astronomical Spring, or the “actual” spring season begins this year on March 19th and goes through June 20th.