Hourly Weather for University City, San Diego

Got story updates? Submit your updates here. ›

The first of March marks the start of spring for meteorologists in the Northern Hemisphere, even though astronomical spring comes much later in the month on the spring equinox. Meteorologist Caitlin Kaiser explains the differences between the two and why meteorologists follow a different seasonal calendar.

Why it matters

The distinction between meteorological and astronomical seasons is important for weather forecasting and reporting, as meteorologists use the March 1 date to align their seasonal data and predictions, while the equinox date is more significant for astronomical and cultural observations of the changing seasons.

The details

Meteorologists define the seasons based on the annual temperature cycle, with spring running from March 1 to May 31, summer from June 1 to August 31, fall from September 1 to November 30, and winter from December 1 to February 28 (or 29 in leap years). This makes the data easier to analyze and report on. Astronomers, on the other hand, define the seasons based on the position of the Earth in relation to the sun, with the spring equinox marking the first day of astronomical spring.

• March 1 marks the start of spring for meteorologists in the Northern Hemisphere.
• The spring equinox, which typically falls around March 20, marks the first day of astronomical spring.

What they’re saying