Meteorologists are so often wrong in their weather predictions because the wind blows where it wills. No one knows where comes from or where it goes. Wind drives many storms and makes them go in a direction that computer models don't see. Weather prediction has to do with the future or the past, not the moment. Because forecasters look into the future and the past, errors occur.
Sometimes the weather forecasts are wrong because the meteorologist has worked at the one location too long. He or she does not believe what the weather service officials say because the specific kind of weather has never happened there. On the other hand, 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. Sometimes they rely too much on technology and not enough on reality.
Computer models help, and they are a tool but they are not infallible. Often they are fallible. That is why the forecasts are wrong. A good meteorologist goes out into the field as well as using the computer tool. If more weather people did that, they would more accurately give a true forecast. Computer models can only see so far in the future accurately. They often do not notice things that cause the jet stream to change.
Another reason for errors in weather prediction is meteorologists base their forecasts on probability. Because of differences in the climate, those temperatures are not the same, so errors occur.
Meteorologists use many maps to follow fronts which produce storms. Because of the amount of data used, choices as to which map, is the right one, cause errors to occur. Even with all the computer help, the weatherperson must make decisions based on what he feels is the most likely weather scenario.
Weather forecasting means forecasting the atmosphere. The atmosphere always changes with natural disasters occurring. Volcanic ash and pollution are two things that make forecasting difficult. Forecasters have a hard time predicting fog conditions. Again, the wind blows at a certain time making it lift or clear. Who knows when that will happen?
Weather forecasters use four different methods: persistence forecast, analoque method, weather types and long-range weather forecasting. These all come with percentages such as 30% chance of snow. This means that snow can fall anywhere that people hear that forecast. Forecasts that are for a day or two are quite accurate. The farther forecasters look into the future, the less accurate the prediction.