MANKATO, Minn. (KEYC) - Have you heard a KEYC New Now Meteorologist refer to March 1st as the start of meteorological spring and reference astronomical (calendar)spring doesn’t start until March 19th for the year 2020? Are you confused as to why meteorological and astronomical spring don’t fall on the same date? Today’s weather blog looks at the difference between meteorological and astronomical spring and why we have both.
Seasons are caused by the slight tilt of Earth’s axis. Earth, on average, is tilted 23.5º from the plane of its orbit around the sun. As Earth takes it elliptical orbit around the Sun, Earth’s tilt and sun’s alignment over the equator determine both the solstices and equinoxes. Solstices indicate the start of either our summer or winter months while the equinoxes indicate the start of our transitional seasons spring and fall. Northern hemispheres winter falls on or around December 22nd solstice while our summer falls on or around June 21st. Spring equinox begins on or around March 21 and the fall/autumn equinox is on around September 21st.
Our solstices and equinoxes will vary year to year due to fact that Earth’s rotation around the sun actually takes 365.2422 days not 365 days. It also varies due to the elliptic path Earth takes as it orbits the sun. To make up for the missing time we add an extra day to the shortest month of the year every 4 years, which we refer to as leap year. Since this year is a leap year our solstice and equinoxes will vary. For the 2020 season our spring equinox will fall on March 19th and run 3 months until our summer solstices starts June 20th. At any given year the astronomical seasons can vary between 89 to 93 days. These constant variations make it very difficult to track climatological data and also makes it difficult when it comes to comparing seasonal climatological data. This is why meteorological seasons were developed.
Meteorologist and climatologist went ahead and made things a little more simple. By using our calendar they broke our seasons down into groupings of three months based on our annual temperature cycle, starting each new season at the beginning of the month. So meteorological spring runs from March 1st all the way to May 31st, June is then the official start of meteorological summer. Summer runs for the next three months until fall arrives on September 1st and then in another three months winter begins. Pretty simple right?
By breaking down the seasons this way the length of days become more consistent running anywhere from 90 days for winter/fall and 92 days for spring/summer. This makes it easier for collecting and calculating seasonal and monthly statistics.
Meteorological spring is commonly pointed out because it means warmer weather ahead for those living in the northern hemisphere. Especially after what seems to be a long bitter winter. It is also commonly pointed out because the meteorological spring is when severe weather begins to increase across the United States. Storm chasers may be getting excited for the first sings of tornadoes, while others may be starting their severe weather preparations.