“Brittsommar” is another ‘grab’ word in Swedish referring to a period of warm weather in fall which is around October 7, St. Bridget’s day.
As SMHI states, it usually settles for fine, warm and sunny weather “typically of Indian summer”. This period marks the last struggles of autumn before the weather turns even colder. Even though the moniker indicates that the phenomenon is strictly observed in the early parts of October, Brittsommar can be experienced in other parts of the autumn season.
This is mostly applicable to warmer months of summer but however does not fit into any pattern or season. SMHI notes that this has been attested for many years due to meteorological factors such as clear skies which bring relief from more moderate conditions rather than the finding of those winter conditions that had already been established. It is a normal weather pattern resulting in temporary warmth because of the influx of warm air mass usually responding from a cool period which ushers fall. In ancient times as described, Brittsommar was prevalent especially to the farming societies as it provided them extra time to carry out their outdoor work including harvesting.
SMHI explains that in addition to the appreciation systems in place to dress in “Indian summer” in the western countries, Brittsomar has gained additional cultural meanings and usage in Sweden as well. As such, it is understood that there will be a period before the winter sets in, when there will be some sunlight. It would be similar to “Indian Summer” of North America and elsewhere where there are episodes of warm weather in autumn.