Assessing the quality of volunteered weather observations

Weather observations are typically collected by professional devices siting in open spaces. These weather stations provide very precise measurements, but they also require a regular maintenance and calibration of the sensors, which implies a high cost for national weather services. In general terms, one could say that we are good with the current weather forecast. In the end, the combination of in-situ measurements with numerical weather models and remote sensing data, provides a decent weather forecast for several days in advance.