Why can weather forecasts change?

Weather forecasts are recalculated regularly. As soon as current measurement data from weather stations, radar systems and satellites become available, they are incorporated into the next calculation. This can cause the expected weather development to change.

New data changes the calculation

To make a forecast, the current state of the atmosphere must be captured as accurately as possible. However, completely seamless measurements are not possible. With each update, new observations become available, which allow the initial state to be estimated more accurately.

This can lead to changes in:

• Temperature,
• Cloud cover,
• Wind,
• Probability of precipitation, and
• The start, duration and intensity of rain or snow.

Small deviations can have greater impacts

The atmosphere is a complex system. Even small differences in the initial state can cause a weather situation to develop differently later than initially calculated.

Particularly with localised events such as showers, thunderstorms or fog, even small shifts in time or space can change the forecast for a specific location.

Uncertainty increases with time period

The further ahead a forecast extends, the greater the uncertainty. However, short-term changes are also possible if new measurement data shows that a weather system is moving faster, slower or in a different direction than previously expected.

A changed forecast therefore does not automatically mean that there is an error. It shows that the expected weather development has been recalculated on the basis of the latest available data.