Weather forecasts can change when updated. Different weather apps also sometimes show different values for the same location and time period. Both are normal and do not automatically mean that a forecast is incorrect.
Why does a forecast change?
Weather forecasts are calculated using weather models. They are based on current observations, for example from weather stations, radar systems and satellites.
Since the state of the atmosphere cannot be measured completely everywhere, every calculation is associated with uncertainties. As soon as new weather data is available, the expected development is recalculated. As a result, the following information can change, amongst others:
- Temperature,
- Precipitation probability,
- Start and duration of rain,
- Cloud cover and
- Wind.
The further into the future a point in time lies, the more subsequent calculations can differ from the original forecast.
Why do weather apps show different results?
Weather providers can use different weather models, data sources and calculation methods. Differences can also arise because:
- the data was updated at different times,
- locations and altitudes are assigned differently,
- local weather conditions are taken into account differently and
- daily values or weather symbols are summarised differently.
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