Summer - Glitchfiend/SereneSeasons GitHub Wiki
Summer is the 2nd season of the year for temperate biomes. It is split up into 3 sub-seasons: Early Summer, Mid Summer, and Late Summer. Each sub-season lasts 8 in-game days by default (NOTE: This can be changed in the configuration settings!).
In Summer, the grass and foliage mellows out to a yellow-ish green tint.
Thunderstorms are also more common in summer.