Flitter and Cloudchaser are in charge of the weather process. Stuck in a dusty control room 24/7 to make sure that the machines work properly. After Rainbow Dash goes home sick, Cloudchaser is in charge of Rainbow's station, leaving Flitter to take care of the machines.
A massive malfunction in the control room appears, breaking the one machine that produces clouds. Without the clouds working correctly, the pegasi ponies have no control over the weather in Equestria. making it snow and rain constantly.
After too much clouds are made, the sun no longer shines.