The seasons are directly related to the changing of the moons during the festival quarters.
The spring and fall moon is just called “the Moon”. It has the normal “silvery” light that we associate with the moon in our own world.
The summertime moon is known equally as the “Fey Moon” or the “Summer Moon”. It seems larger in the sky and its light takes on a slightly golden tinge so that it’s almost like a minor sun in the sky, and its light actually gives out a little warmth at night, though that may only be psychological.
The wintertime moon is known as the “Shadow Moon” or “Winter Moon”. It is smaller in the sky, and always has a dark blood-reddish tinge. Its light is never as strong, and on days (or nights) when it is full, it seems to add a further chill to the air.
When summer starts, the days slowly start getting longer. They keep slowly getting longer until the Summer Moon transitions back. Over the next two months the days return to normal – equal lengths of day and night.
When winter starts, the days grow shorter and continue to shorten until the festival of Returning. It takes the first two month of spring before the days and nights are equal again.
The strength of the Sun also plays a part in the weather, and for some reason the sun is stronger at the equator of the world and weaker at the poles. Because of this the poles are more greatly affected by the change in moons, and the equator is less affected.
In this cosmos, the Feywild is known as the Summerland. The Shadowfell is more commonly referred to as the Winterfell instead.
The Summerland is always bright and summery except for the three months when its moon is in the middle world. Then it cools somewhat, and the days become more spring-like and rainy.
The Winterfell is always dark and cold except for the three months when its moon is away. Then it thaws somewhat, and the days feel like late autumn, warmer, but still with the scent of death and winter on the air.