When does spring start? What to know about the vernal equinox

Flowers are starting to bloom, days are getting longer, and temperatures are increasing… that only means one thing… spring is on the way!

Spring officially begins in the Northern Hemisphere on March 19 with the vernal equinox as the entire world experiences an equal amount of daylight and darkness.

For ease of recordkeeping, meteorologists and climatologists consider March 1 the first day of spring, but astronomically speaking, the Earth’s equator is aligned directly with the Sun on the vernal equinox. In 2024, that occurs March 19 at 11:06 p.m. EDT.

SAN FRANCISCO, CA - MARCH 13: A kid enjoys the scenery of blooming tulips at Golden Gate Park on March 13, 2024 in San Francisco, California. (Photo by Liu Guanguan/China News Service/VCG via Getty Images)

Astronomical seasons are based on the position of the Earth with respect to the Sun as the planet makes its annual revolution around the closest star.

The Earth is tilted approximately 23.5 degrees off a vertical axis, and because of this tilt, the most direct sunlight is aimed at the Southern Hemisphere during our astronomical winter and at the Northern Hemisphere during our astronomical summer.

The two solstices and two equinoxes are simply precise moments in time when the Sun is in direct alignment with three distinct bands of latitude.

Their dates can vary by a day or two each year since it takes the Earth 365 days and 6 hours (365.25 days) to make one full revolution around the Sun, which is why we have a leap year every four years.

Weather Forecast 

While spring is almost here, the rain returns yet again to parts of Southern California. 

A low-pressure system is expected to drift over the region by Monday afternoon, bringing a chance of some precipitation.

"High resolution models suggest that the showers could start as early at 3-4 p.m. this afternoon in the Los Angeles and Ventura County mountains," according to the National Weather Service. "Retaining a widespread low possibility of rain and thunder in the forecast for this afternoon for all of LA, Ventura, and (Santa Barbara) counties."

Forecasters said there is a "slight chance" of showers or thunderstorms to occur. Any such storms that develop could be accompanied by strong winds gusting up to 50 mph as well as dry lightning.

"There is also a slight chance of hail as colder air aloft moves into the region," forecasters said. "There could also be brief heavy downpours near the cores of any storms, but any downpours should be brief since strong northeast flow aloft should keep storms moving rather quickly."

According to the NWS, some residual moisture will likely linger into Tuesday, bringing another chance of afternoon showers or storms, but the weather should calm by Wednesday, with above-normal temperatures anticipated by Thursday. Some clouds are anticipated by Friday, lowering temperatures closer to normal.

FOX Weather and City News Service contributed to this report