Weekend Weather Blog: What is Meteorological Spring?

TWIN FALLS, Idaho (KMVT/KSVT) – Over the next few days you will hear a term called meteorological spring. It starts on March 1st every year and ends on June 1st every year. However, maybe you are used to spring starting at the end of March – on the 21st or 20th (depending on the year). You would say that correctly. Why are we talking about pain now?

If you were to ask an astronomer (someone who studies space), he or she would tell you that spring begins in late March, and that would be correct. As the earth orbits the sun, the tilt of our axis affects certain areas that see direct sunlight year-round.

During summer in the northern hemisphere, the northern half of the earth is tilted toward the sun, while the southern half is tilted away from the sun. The result is more direct sunlight in the northern hemisphere.

Axis tilt June-Aug(Nicholas Snider)

Conversely, during northern hemisphere winter (late December to late March), the northern half of the earth is tilted away from the sun and the southern half of the earth is tilted toward the sun. The result is more direct sunlight toward the southern hemisphere.

axis inclination winter
axis inclination winter(Nicholas Snider)

However, what happens on the first day of spring and autumn? Direct sunlight is seen everywhere on earth. These are known as the equinoxes, and these two days (late September and late March) represent the first days of spring and fall.

However, meteorologists look at the seasons a little differently. Rather than basing this on length of days and who sees the most direct sunlight, let’s simply look at each month’s typical weather patterns. How often do you see the thermometer hit 90° in early June? Quite often – about as often as you see snow in early December.

For this reason meteorologists unofficially consider the start of a season to be on the first of every third month, with spring beginning on March 1st, summer on June 1st, autumn on September 1st and winter on December 1st. So next time you hear the term meteorological spring, the earth’s position around the sun may not be complete, but the weather may be saying otherwise.

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