Every update begins with a new picture of the atmosphere
Weather stations, satellites, radar, buoys, aircraft and weather balloons observe different parts of the atmosphere. Through data assimilation, these measurements are combined with a previous forecast to produce the most consistent possible estimate of temperature, wind, humidity and pressure at the start of the new calculation.
Observations cannot cover every location and altitude and inevitably contain uncertainty. Models must also approximate processes that are too small or complex to represent directly. A new update is therefore not simply a correction of an earlier mistake: it is a fresh calculation based on the latest available evidence.
One scenario cannot describe all the uncertainty
The atmosphere is a chaotic system, so very small differences in its initial state can grow over hours and days. The arrival time of a front, the position of a rain band or an exact temperature value may change even when the broader weather pattern remains similar.
Ensemble forecasts address this problem by running several simulations with slightly different initial conditions and model representations. Agreement among many members indicates a more robust signal; a wide spread indicates a broader range of plausible outcomes and a need for greater caution.
How to compare updates without chasing every fluctuation
Compare the same location and valid time across several consecutive updates. Look for persistence in the type of weather, timing window and affected area instead of focusing on one exact value. A signal repeated across model cycles and supported by the ensemble is more informative than a peak shown by only one simulation.
As an event approaches, additional observations generally help to constrain the forecast, but thunderstorms, fog, snow and other local phenomena can remain difficult to place precisely. For weather-sensitive decisions, keep flexible options and always consult bulletins and warnings from the competent authorities.
Sources and method
Practical example on Meteo Interactive
For the same place and valid time, compare two successive updates and check their source and update time: a change reflects new information and is not necessarily an error.
This guide is explanatory content kept separate from operational weather data. It was checked against the public sources listed below and against the labels, units and times actually shown on the site. The review checks clarity, consistency and the distinction between observations, forecasts and official warnings; the text is updated when a source or the interface changes.
If you find an error or an outdated reference, report it to the editorial team.
Forecasts describe likely scenarios and do not replace alerts or official authority communications.