According to Greek mythology, halcyon days are

the seven days in winter when storms never occur. [Wikipedia]

I assume that Ancient Greeks noticed a period in winter during which the weather was especially calm, so they came up with a myth to explain it.

Is there such a concept in meteorology?

According to the article “Halcyon Days: When Spring Appears in the Middle of Winter in Greece” from Greek Reporter, the Halcyon days supposedly take place some time between 15 December to 15 February, most often between 16 to 31 January.

  • 1
    $\begingroup$ As someone who had lived on the Mediterranean coast for most of my life, I can assure you that any period of seven days without storms is extremely common. Mediterranean winter is usually just cold with long time of nothingness punctuated by short periods of storms and rainfall. $\endgroup$
    – Gimelist
    Jan 16 at 5:30

The story of Halcyon days is that there is a period of 7 (or 14?) days around midwinter (on the 21st of December) on which Aeolus does not make the wind to blow - to allow the Kingfisher, 'Alcyone to lay her eggs. This is a myth.

There is no predictable period of calm weather in midwinter, although periods of stormy and calm weather can alternate, on several time scales. There are periods of a week or so that are calm, but they do not occur regularly.

There are lots of examples of storms in the Mediterranean and across the Northern Hemisphere, occurring on or near to the 21st of December, the time when according to the myth, storms don't occur:

[In] 1967 An F4 tornado traveled 33 miles across Iron and Washington Counties in Missouri [...] The tornado killed 3 and injured 52 others. (source)

[In 2021] Severe weather forecast across much of Greece and Cyprus due to Storm Carmel through at least Dec. 20. (source)

Of course there are more stormy and less stormy days. Most, if not all winters will have a period of high pressure, with gentle winds and little preciptiation. These can last a week or more. But you cannot predict with accuracy when these periods will occur from more than a few days in advance.

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    $\begingroup$ Does the myth say that the Halcyon days are supposed to be near the 21st of December? I have not come across this specific date. $\endgroup$
    – hb20007
    Jan 15 at 10:01
  • $\begingroup$ As I understand from the article I linked to in my question, it's not supposed to fall on the same calendar days every year. $\endgroup$
    – hb20007
    Jan 15 at 13:43
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    $\begingroup$ Yes, they are supposed to be the days around the winter solstice. Otherwise the claim is trivial. Yes, there are some days in winter that are not stormy! The only interesting part of such a claim is that these days occur in a regular manner: that there is a period of quiet weather in the middle of winter, on the 7 days around the 21st of December. $\endgroup$
    – James K
    Jan 15 at 21:05

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