<p>As JeopardyTempest commented: Actually, the astronomical seasons are defined in such a way that you should expect them to be a full 1 ½ months behind, not just 21 days! Namely, astronomical winter only <em>starts</em> at the winter solstice, astronomical spring only <em>starts</em> at the equinox etc.. A more intuitive definition would arguably be if the seasons were <em>centered</em> around these events. I.e., the astronomical seasons have ⅛ year lag built in.</p>

<p>This intrinsic misalignment is partially cancelled by another delay, the <a href="https://earthscience.stackexchange.com/questions/4505/why-is-march-colder-than-september-in-northern-hemisphere">seasonal lag</a>, which is in most places about a month. I.e. the temperature-defined meteorological seasons also lag behind the Earth's orbit, but by less than the astronomical seasons; the observation that the astronomical seasons lag behind the meteorological seasons by 21 days is just an alternative view point.</p>

CC BY-SA 3.0
2018-03-02T11:09:04.920Z
2018-03-02T11:09:04.920Z
leftaroundabout
<p>In meteorology the seasons always start at the beginning of the month the astronomical seasons start.<br>
The astronomical seasons start around the 21st in a month so I guess it would make more sense to start the meteorological season at the first day of the month following the start of the astronomical season.<br>
Another more logical reason to do this: for example the meteorological winter start at December 1 and ends at February 28 (or 29) in the next year so meteorology actually measures in broken years. Should the meteorological winter start at January 1 and end at March 31 then all seasons do exactly fit in the same year.<br>
So is there a reason why meteorologists do it this way or is it just arbitrarily chosen?</p>

<meteorology><seasons><astronomy>
Why do meteorological seasons start earlier than astronomical seasons?
wie5Ooma
# Why do meteorological seasons start earlier than astronomical seasons?

(Asked by: username_0 on 2018-03-02)

In meteorology the seasons always start at the beginning of the month the astronomical seasons start.  
The astronomical seasons start around the 21st in a month so I guess it would make more sense to start the meteorological season at the first day of the month following the start of the astronomical season.  
Another more logical reason to do this: for example the meteorological winter start at December 1 and ends at February 28 (or 29) in the next year so meteorology actually measures in broken years. Should the meteorological winter start at January 1 and end at March 31 then all seasons do exactly fit in the same year.  
So is there a reason why meteorologists do it this way or is it just arbitrarily chosen?

**Tags:** meteorology, seasons, astronomy


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## 1 answers

### Answer by username_1 on 2018-03-02. Score: 3

As JeopardyTempest commented: Actually, the astronomical seasons are defined in such a way that you should expect them to be a full 1 ½ months behind, not just 21 days! Namely, astronomical winter only *starts* at the winter solstice, astronomical spring only *starts* at the equinox etc.. A more intuitive definition would arguably be if the seasons were *centered* around these events. I.e., the astronomical seasons have ⅛ year lag built in.

This intrinsic misalignment is partially cancelled by another delay, the [seasonal lag](https://earthscience.stackexchange.com/questions/4505/why-is-march-colder-than-september-in-northern-hemisphere), which is in most places about a month. I.e. the temperature-defined meteorological seasons also lag behind the Earth's orbit, but by less than the astronomical seasons; the observation that the astronomical seasons lag behind the meteorological seasons by 21 days is just an alternative view point.


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