Early
Day 1-7
Mid
Day 8-14
Late
Day 15-21
Early
Day 22-28
Mid
Day 29-35
Late
Day 36-42
Early
Day 43-49
Mid
Day 50-56
Late
Day 57-63
Early
Day 64-70
Mid
Day 71-77
Late
Day 78-84

• The four seasons are split in three sections called 'early', 'mid' and 'late'.
  
• Each section consists of 7 days and during midnight it will switch to a new season.
  
• Days themselves are 30 minutes long. 15 minutes daytime and 15 minutes nighttime.
  
• By pressing f8, graphic setting and then weather one of the variables is called FrontTransition.
  
• The FrontTransition is the best what we have for ingame time. Whenever it reaches 1 it will switch between day and nighttime.
  
• The game doesnt mention when the year changes so it is difficult to determine wether it follows the same irl logic.
  
• To make overview easier i'll leave early spring as the beginning of the year and late winter as the end of the year. (This is prone to change)
  
• Community Tab day count always updates on high noon. In comparison the season change always updates on midnight. It's more logical to rely on midnight for new days to reflect real life standarts.

(Volatile temperature changes due to rain and occasional snowfall)
Early
Clear weather ~ 5°C Day / 0°C Night
Clear weather highest recorded temperature 6°C Day / 1°C Night
Snowfall lowest recorded temperature -7°C Day / -12°C Night
Mid
Clear weather ~ 12°C Day / 7°C Night
Clear weather highest recorded temperature 23°C Day / 18°C Night
Snowfall lowest recorded temperature 6°C Day / 1°C Night
Late
Clear weather ~ 18°C Day / 13°C Night
Clear weather highest recorded temperature 25°C Day / 20°C Night
Clear weather lowest recorded temperature 14°C Day / 9°C Night
(High temperature spikes and occasional rain)
Early
Clear weather ~ 22°C Day / 17°C Night
Clear weather highest recorded temperature 36°C Day / 31°C Night
Clear weather lowest recorded temperature 18°C Day / 13°C Night
Mid
Clear weather ~ 26°C Day / 21°C Night
Clear weather highest recorded temperature 34°C Day / 29°C Night
Clear weather lowest recorded temperature 24°C Day / 19°C Night
Late
Clear weather ~ 27°C Day / 22°C Night
Clear weather highest recorded temperature 31°C Day / 26°C Night
Clear weather lowest recorded temperature 13°C Day / 8°C Night
(Volatile temperature changes due to rain and occasional snowfall)
Early
Clear weather ~ 25°C Day / 20°C Night
Clear weather highest recorded temperature 37°C Day / 32°C Night
Clear weather lowest recorded temperature 22°C Day / 17°C Night
Mid
Clear weather ~ 22°C Day / 17°C Night
Clear weather highest recorded temperature 22°C Day / 17°C Night
Snowfall lowest recorded temperature 3°C Day / -1°C Night
Late
Clear weather ~ 10°C Day / 5°C Night
Clear weather highest recorded temperature 10°C Day / 5°C Night
Snowfall lowest recorded temperature 5°C Day / 0°C Night
(Extreme colds and occasional rain to clear the snow)
Early
Clear weather highest recorded temperature 1°C Day / -3°C Night
Clear weather lowest recorded temperature -10°C Day / -15°C Night
Mid
Clear weather highest recorded temperature 5°C Day / 0°C Night
Snowfall lowest recorded temperature -14°C Day / -19°C Night
Late
Clear weather highest recorded temperature 5°C Day / 0°C Night
Snowfall lowest recorded temperature -16°C Day / -21°C Night

• Weather changes or day/night shifts are the only factors that affect temperature.
  
• Otherwise the temperature would remain constant throughout the year.
  
• Day/Night shifts change the temperature up 5 Celsius for daytime and down 5 Celsius for nighttime.
  
• Rain itself can lower or raise temperature. It can go up to 31 recorded temperature during summer.
  
• Snowfall can happen sometimes during Fall or Spring and will always occur during Winter.
  
• The temperature during Winter can dip down to -26 celcius.

I'm in the middle of making a farming guide and investigated the seasons in addition.
It's a small guide but it gives a good overview on how many days are left until winter.
Will update in the future.