There are a number of ways to denote the start date of spring. Meteorological Spring consists of the full months of March, April and May. The Astronomical Spring is the period between the spring equinox and summer solstice and due to the Earth's eccentricity and leap days, the period is not exactly the same period of days each year. So we have either been in spring for a few days or a few weeks depending on how you count. Another way to compute the spring period is to split the year into 91 day chunks and then have spring start after the coldest 91 consecutive stretch of days ends. The featured chart does just that and shows the end dates of the coldest and warmest 91 day stretch each year. If you then back out the period of days between the coldest and warmest stretch, you end up with spring! The bottom two panels provide some long term metrics for the number of days and start date for Ames. This metric indicates spring starting on March 9th, so that's the answer!

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Tags:   spring