Therefore, the boiling temperature increases with pressure. The triple occurs at a specific temperature. Therefore, if we observe all three phases, we know exactly what the temperature must be. This is different from the behaviour of sublimation, melting and boiling temperatures which all vary with pressure. The temperature generally drops overnight.
Vapour pressure decreases when the temperature is reduced.
If the temperature drops enough, the partial pressure of water in the air becomes greater than the vapour pressure. The water vapour is no longer in equilibrium and it condenses. Since this is a solution, the solvent generally freezes out first. Once freezing starts, removal of heat thus causes some solvent to freeze, which leaves behind a more concentrated solution whose temperature can thus drop a little more.