High Winter is the day when the planet is furthest to the sun. It is a solemn day of remembering people and events from the past. In the north, it is a reminder that there will always be sorrow. The southern cultures see High Winter more as a day of prosperity. It is the best day to get out and get work done, because it should be the coolest day of the year. (This is not exactly true, because the days that follow also have the planet distant from the sun and have less heat “sunk” into the planet’s surface.)
Fletnern is in an elliptical orbit around its sun. This slight offset to the distance between the planet and the sun causes the seasons as the planet is physically farther from the sun during winter.