Seven Sleepers' Day

Its Western version was part of the widely distributed Golden Legend hagiography collection compiled by Jacobus de Voragine about 1260.

The cult became common during the Crusades of the High and Late Middle Ages, and June 27 was declared a commemoration day in most of the Catholic dioceses.

The Islamic version includes more details such as the mention of a dog, who accompanied the youths into the cave and appears to keep watch.

Based on this date the prediction has a slightly increased probability of about 55–70%, if confined to the southern parts of Germany, where the rule seems to have originated.

Depending on the meandering flow of the polar jet stream in the Northern Hemisphere (Rossby waves) and the emergence of veering low-pressure and high-pressure (anticyclone) systems, the atmospheric conditions tend to stabilize in early July: either a high-pressure ridge takes hold over Scandinavia, which may coalesce with the subtropical Azores High to form a stable and warm macro weather situation; or a high North Atlantic oscillation between the Icelandic Low and the Azores High implies a long-standing influx of wet air masses into Central Europe.