TAMPA, Fla. (WFLA) – There is a reason the phrase “in like a lion, out like a lamb,” is used to describe March. March kicks off the transition season from the cold winter months to the warm summer months.
However, astronomical spring doesn’t begin until March 19th at 11:49 p.m. according to timeanddate.com. Last year, astronomical spring landed on March 20th. The start of astronomical spring is determined by astronomy; when the sun passes over the equator from the southern hemisphere to the northern hemisphere. This is also known as the vernal equinox, when the length of day and length of darkness are nearly the same, or equal.
Unfortunately for meteorologists and climatologists, the vernal equinox (as well as the fall equinox, the winter and summer solstices), occur at different times year to year meaning the start date of seasons change year to year as well.
Not only do the start date of the seasons vary year to year but the length of the season does as well, as do all the seasons. This is makes it difficult for meteorologists to compare statistics from year to year on the seasons.
For this reason, meteorologists think of seasons differently. Instead of the vernal equinox marking the start of spring, March 1st marks the first day of “meteorological spring”.
For consistency purposes, all four seasons are broken up into three month groups and are the same every year. Spring, for example, starts March 1st and runs through April and all of May before meteorological summer begins on June 1st.
Summer runs June, July and August. Fall starts September 1st, runs through October and November and finally meteorological winter is during the months of December, January and February.
These months are not chosen arbitrarily, they line up well with the annual temperature cycles.
This allows not only the individual season lengths to stay the same year to year (with the exception of spring in leap year,) it also allows the four seasons to be closer in length when compared all together. For example, summer is 92 days long while meteorological fall lasts 91 days.
According to NOAA, this makes it easier to calculate seasonal statistics from the monthly statistics which end up being useful for agriculture, commerce, and a variety of other purposes.