Forecast accuracy tends to decrease with time. This is because small scale processes and errors in the data magnify with time. The 24-hour forecast tends to be most accurate. The 2 to 3 day forecast can be fairly accurate. Beyond 3 days it is common for the forecast to be off. There are cases where the longer term forecast can be more accurate. This can occur when a weather system is moving through in the short term and then a stable weather pattern builds in during the longer term forecast. Weather that is changing tends to be forecasted less accurately compared to a stable and persistent weather pattern. In the future, long term forecasts will improve as computing power continues to increase, weather data increases and solutions methods continue to be made more sophisticated. There will always be uncertainty in long term forecasts but that uncertainty will be reduced. |