A weather substation was a surface-based facility used to monitor, support, and operate a planetary weather control system.
The Caldos colony had an older weather control system, that rarely received heavy maintenance. In 2370, the substations were still operating on late-23rd/early-24th century controls, and power was distributed using an electro-plasma system.
While the USS Enterprise was in orbit of Caldos, Governor Maturin took advantage of the rare opportunity to have a starship engineer take a look at the weather control systems. When one of the weather substations that regulated atmospheric humidity began experiencing a power failure, the Enterprise tried a power transfer beam to the substation. When the power transfer created a feedback loop with the Enterprise, Data and Geordi La Forge beamed down to the substation to check why the backup systems weren't functioning, and found Ned Quint dismantling the primary plasma conduit. (TNG: "Sub Rosa")