If the instruments used to record the weather data are not of good quality or are not properly calibrated, then the data recorded will not be accurate. Similarly, if the weather station is located in an area that is not representative of the local climate, or if it is affected by nearby buildings or trees, then the recorded data may not be accurate.
In addition, the personnel responsible for maintaining the weather station and recording the data must be properly trained and have a good understanding of the instruments they are using. If they are not properly trained, then there is a higher likelihood that errors may be introduced into the data.