When’s the first day of spring? Here’s what you need to know

When’s the first day of spring?

If you ask an astronomer when the first day of spring is this year, they’ll say March 20, 2025, at 9:01 UTC (4:01 a.m. CDT). But if you ask a meteorologist or climatologist, they’ll tell you spring starts March 1. How are there two different spring seasons? Read on to find out why astronomical spring and meteorological spring differ.

Astronomical spring

Earth has a 23.5-degree tilt as it orbits the sun. This tilt toward or away from the sun determines the seasons we feel across the globe. The spring (or vernal) equinox occurs when the sun passes over the equator from south to north and marks the start of warmer months across the Northern Hemisphere.

Because astronomical spring is tied to the rotation of Earth and the exact moment the sun crosses the equator, the first day of the spring season can shift by a day from year to year. This also means the length of the spring season can vary. Likewise, the autumnal equinox, or start of fall, can also have different start dates.

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Meteorological spring

Meteorological spring starts on March 1 and runs through May 31 every year, regardless of the exact moment of the vernal equinox. This allows the seasons to be more consistent, which is important when looking at weather data, especially temperatures. With more consistent seasons, meteorologists and climatologists are able to better analyze temperature trends and precipitation patterns across a set period of time. Calculating a seasonal average is much easier when that season starts and ends on the same day year after year.

Spring weather

Spring is a transition season in the Northern Hemisphere. It’s as simple as it sounds. During the spring season we are transitioning out of the colder winter months into the warmer months of spring and eventually summer. This also means our weather tends to be more active. The dramatic changes from cold to warm can create chaos, with severe weather outbreaks and late-season snowstorms. Plus, frosts and freezes well into the spring growing season can have an impact on sensitive crops.

As temperatures start to warm across North America, colder air from the Arctic can still spill down with dips in the jet stream. (The jet stream is the band of strong winds in the upper levels of the atmosphere that separates the warm and cold air.) This class of colder air colliding with warm, moist air can create an environment in which severe storms can develop.

Severe storms (and severe storms capable of producing tornadoes) can happen in any season. But they’re most common in the spring and summer months as temperatures warm. Severe storms that produce tornadoes are more common in spring across the Gulf Coast. But across the Plains of the United States, the typical tornado season is from late spring into early summer.

First day of spring is a reminder of thunderstorm and tornado safety

Early spring is a great time to remember severe weather safety! Only 10% of all thunderstorms in the United States go on to become severe. A severe thunderstorm is defined as one with winds of more than 58 miles per hour (93 kph) and/or hail 1 inch (2.5 cm) or greater in diameter. But all thunderstorms are dangerous due to the presence of lightning. If you can hear thunder, the storm is close enough for you to be struck by lightning. As soon as a storm is nearby, go inside a building or vehicle to wait out the storm, and wait at least 30 minutes from the last lightning strike to resume any outdoor activities.

In the event of a tornado, time is vital. As soon as a tornado warning is issued, go to the lowest level and most central part of your home or building. An interior closet or bathroom away from outside walls and windows is best.

If you live in a mobile home, you need to get out and find another place to shelter. The strong winds of a tornado can pick mobile homes up off the ground. If there is a risk of tornadoes and you live in a mobile home, contact a trusted neighbor or family member who has a basement or shelter of some kind that you can stay in until the threat of tornadoes has passed.

It’s the same for those out on the road: You are not safe in a car during a tornado. Get off the road and find a business or shelter to wait out the tornado.

Spring outlook 2025

So what will this spring bring us? In general: a good portion of the country will have higher chances of above-normal temperatures, while the Great Lakes, Ohio Valley and Pacific Northwest have higher chances of being wetter than normal.

Bottom line: While astronomical spring doesn’t start until March 20, meteorologists and climatologists use March 1 as the start of spring for consistency.

Via NOAA