Ask a meteorologist: What's the difference between meteorological and astronomical spring?

The most recognizable impact on the ground is the amount of daylight, which is approximately 12 hours on that day, regardless of where you are on Earth.

To be complete, this marks the moment of the spring equinox, when neither the northern hemisphere nor the southern hemisphere are tilted toward the sun. This tilt of Earth on its axis fluctuates between 22.1 and 24.5 degrees over 41,000 years but, during our lifetimes, the angle is a relatively consistent 23.5 degrees.

So for the past few weeks, we have been in this nebulous period between the start of meteorological spring and astronomical spring.

Earth’s orbit around the sun is not a perfect circle, and it is slightly closer to the sun in January. As a result, the speed of Earth around the sun is not the same all year long. It does not change much, but the change is perceptible. Plus, Earth does not go around the sun in exactly 365 days. It takes an additional six hours, which is why we add a day to the calendar every four years.

The result is that astronomical seasons do not always start at the same time on our calendar. Over the next 20 years, astronomical spring starts as early as March 19 at 7:20 p.m. and as late as March 20 at 4:25 p.m.

For meteorologists and climatologists, this makes record-keeping a challenge.

Meteorological seasons were born from this dilemma. Since people are more familiar with calendar months versus the precise moment that an astronomical season arrives, the climatologically hottest and coldest three-month periods are used to keep records for the seasons. The three hottest months are June, July and August. Conversely, the three coldest months are December, January and February.

This gives March, April and May the distinction of meteorological spring. But with that, it is important to remember that cold weather and snow are to be expected in March. Early spring marks the beginning of a three-month battle in the atmosphere, as cold air retreats gradually toward the pole in favor of the prolonged warmth of summer.

Despite what we might remember from grade school, spring is not a pristine series of afternoons in the 60s and 70s. Quite the opposite, spring is a weather free-for-all. Freezes are common early in the spring, with the occasional snowfall still hanging on, yet temperatures can still briefly surge into the 90s by the final week of March. The battle scars of spring are seen in the most violent weather of the calendar year; it is the season when hail and tornadoes are most common.

To complicate matters, there is a third way to define the seasons. Breaking the calendar year into four equal parts, solar summer is the quarter of the year when the days are longest and the sun is highest in the sky: May 5 to Aug. 4. Conversely, solar winter is the quarter of the year with the shortest days with the lowest sun angle: Nov. 7 to Feb. 6.

Which puts the spring equinox right in the middle of the solar spring.

No matter how you celebrate and observe, happy spring!