By WeatherBug Chief Meteorologist, Mark Hoekzema
UPDATED March 20, 2014

Most people consider the first day of spring to be the Spring Equinox, which started this year at 12:57 p.m. EDT, March 20th. This is because, astronomically speaking, the sun is directly overhead of the Equator as the Earth`s tilt begins to point the northern hemisphere towards the sun.

As the earth rotates around the Sun, the Sun will be situated directly overhead at mid-day at different times of the year. The Vernal (Spring) Equinox is the day the Sun is again highest in the sky at noon over the equator as the apex progresses north. The day the Sun is straight up at noon over the Tropic of Cancer and Capricorn (23.5 degrees N and S latitude) are the summer and winter solstices, respectively.

Many refer to Astronomical Spring on March 20, as the first "official" day of spring. Most meteorologists will argue that spring begins several weeks before, on March 1st.

That`s because meteorologists observe seasons over different time periods. Meteorological spring began March 1, summer begins June 1, fall begins on September 1 and winter begins on December 1.

There are a couple of very important reasons why this is the case. The most important is for climate record-keeping. Climatologists require set time periods to calculate averages and do seasonal comparisons over the years. Astronomical dates will fall on different days depending on the year, and keeping seasonal climate records based on those dates would be confusing and inaccurate.

A second reason is that weather-wise, it makes more sense around the globe. In spring, mild surges of air from the south are becoming a regular occurrence and severe weather threats begin to kick in by March 1. The heat of summer has been experienced in most areas across the country by June 1 and the heat of summer is waning by September 1.

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Story image: Spring Crocus in Chapel Hill, N.C., submitted by WeatherBug user C. Christopher.

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