The precipitable water vapour (PWV) is the main absorber in the Earth's atmosphere at infrared (IR) and microwave wavelengths. In the last years, the IAC Sky team has been providing real-time PWV data from a monitor based on the GNSS (GPS) technique (GNSS PWV Monitors; GPM). Among other things, the PWV values help in the scheduling of the telescopes with IR instrumentation. The GPM have undergone a continuous process of upgrading. More recently, we have undertaken the PWV forecasting. We will present in the talk a brief summary of the monitors and details of ForO ("Forecasting the Observatories"), the forecasting system for PWV at the Observatories. ForO is based on a mesoscale Numerical Weather Prediction (NWP) model. The ForO system has been validated and calibrated with PWV data from the GPM and will deliver accurate PWV daily predictions for ORM and OT on a 24, 48 and 72 hours windows. This is a definitive improvement to optimize the flexible scheduling for IR observations, in particular for CanaryCAM and EMIR at the GTC.