1) Relying on computers and not going to the field. Sometimes a technical or software fault could lead to a wrong prediction. it could be a new forecaster who does not know the weather patterns and so follows the computer model instead of stepping outside and actually feeling the weather
2) The atmosphere always changes with natural disasters occurring such as pollutants in the air that make forecasting difficult.
3) Most of the times meteorologists base their forecasts on probability. Because of differences in the climate, those temperatures are not the same, so errors occur.
Hope this helps
