This is a table of the temperatures of seasons according to the version "ToughAsNails-1.11.2-2.1.0.36-universal" by default.

Early_Spring 4 -> The temperature transition between late winter to early spring is too high.
Mid_Spring 6
Late_Spring 4 -> For some reason it lowered

Early_Summer -5 -> ????
Mid_Summer 0
Late_Summer 2

Early_Autumn 2
Mid_Autumn 0
Late_Autumn -3

Early_Winter -7
Mid_Winter -15
Late_Winter -10

Fixed for 1.12, and a fix for 1.11.2 will be coming shortly, although you can just swap the spring/summer temps in the meantime.

I have already done that but thanks!