Meteorologists do not promise the weather, but predict it, and this process is not divination, but a complex scientific work based on physics, mathematics, and enormous computing power. Here is how it happens step by step.

Step 1: Collection of Data on Current State

All starts with answering the question: “What is happening right now?”. Meteorologists collect data from all over the world and do this almost in real-time. Sources of information:

• Ground stations. Measure temperature, pressure, humidity, wind, and precipitation at the earth's surface.
• Satellites. Provide about 80% of all information about the current state of the atmosphere, especially over oceans and inaccessible areas.
• Radar. Track precipitation and dangerous phenomena at relatively low altitudes.
• Aerological balloons and aircraft. Measure parameters in the upper layers of the atmosphere.

All these data undergo control: erroneous values are discarded, information is matched and absorbed to create the most accurate map of the initial state of the atmosphere.

Step 2: Calculation on Supercomputers (Numerical Forecast)

This is the heart of modern meteorology. The received data are loaded into a numerical weather prediction model — a complex software complex that solves a system of equations describing the physics of the atmosphere.

The atmosphere is divided into millions of virtual cells (grid). The supercomputer calculates how temperature, pressure, and wind in each cell will change in a few seconds, then uses this result as a new starting point for the next step, and so day by day. That's why some of the most powerful computers in the world are needed to calculate the forecast.

Step 3: Evaluation of Uncertainty (Ensemble Forecast)

The atmosphere is a chaotic system. A tiny error in initial data can grow into a huge error in a few days. To account for this uncertainty, an ensemble forecast is used.

Instead of one calculation, the model is run multiple times (often up to 99 times), each time slightly changing the initial conditions. If all runs show a similar result (for example, rain), confidence is high. If there is a large scatter (one run — rain, another — sun), the forecast is less reliable.

Step 4: The Meteorologist's Work (Post-processing and Experience)

The computer gives a raw result. A meteorologist is not an operator of the machine, but an expert who:

1. Compares data from different global models (European, American, Japanese, etc.).
2. Corrects them, knowing the systematic errors of each model (post-processing).
3. Applies knowledge of local specifics: relief, breezes, the influence of the city, which a rough model may not take into account.

For example, the model may not see a local downpour in a specific area, but the meteorologist, knowing the behavior of atmospheric fronts in this region, will refine the forecast.

Why Forecasts Are Not Always Accurate and How Reliable They Are

The main enemy of accuracy is chaos and incompleteness of data. It is impossible to measure the state of the entire atmosphere perfectly.

Today's 5-day forecast is as accurate as a 3-day forecast in the early 2000s. This is the result of improved models and increased computing power.

Conclusion

Weather forecasting is a chain of “data → supercomputer → ensemble → meteorologist's experience”. And although absolute accuracy will never be achieved, modern technologies allow predicting the weather a few days in advance with a high degree of reliability.

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