Weather forecasts can be classified depending on the time of the forecast, the area and the method of forecast.
The basic parameters describing the state of the atmosphere are the pressure, temperature, speed and direction of the wind. The associated values such as cloudiness, haze, sea condition, atmospheric pollution are also elements of weather forecast and often depend on the forecast of basic elements.
The weather forecast depends on the quantity and quality of the initial data. Due to the chaotic nature of processes describing the development of atmospheric phenomena, the weather forecast becomes less and less accurate over time.
How do we get weather forecast?
Weather forecasts were developed locally for thousands of years on the basis of knowledge of local weather conditions. An example of a weather forecast is Groundhog Day.
The method based on the accumulation of local knowledge or oral communication is often effective – although the forecast tomorrow will be the same as today it works in 70%. The synoptic method is based on the collection of initial data from various sources. Data is systematized and applied to synoptic maps. From a few previous weather maps, based on an understanding of weather phenomena, and based on a subjective assessment, the synoptic evaluates changes that will occur. The numerical models are a modern method of weather forecasting. Most models are based on statistical methods or basic physics principles.
Measurements of meteorological parameters are carried out directly or indirectly, ie remote sensing methods. Traditional observations of wind speed on the Earth’s surface, pressure, temperature, precipitation, atmospheric discharges, cover and type of clouds are made at meteorological stations by special observers or by automatic measuring stations. The World Meteorological Organization (WMO) standardizes the measurement procedures and methods of data transmission through the global meteorological network. An important element of the measurements are aerological surveys of the upper atmosphere. They consist of measurements sent to the Earth by means of a meteorological probe attached to a meteorological balloon. The probe contains basic instruments such as pressure or temperature measurement. The next measurements of the balloon’s position can be deduced about wind speed and direction. This type of synoptic, or simultaneous, measurements all over the world are made by measuring stations every 12 hours (the synoptic word comes from the Greek word syn – at the same time, and optic – visible, i.e. visible at the same time). Similar surveys can be obtained from taking off and landing passenger planes. A big problem in collecting data are ocean areas. Here, measurements from ocean buoys, measurements from ships, and satellite measurements are used.
Data assimilation plays an important role in the analysis of meteorological data. This is due to the fact that meteorological data come from various sources – satellite measurements, direct measurements, radar measurements, or lidar measurements made at different times and in different places on the globe. Data assimilation is a very complex process and can be split into two processes; (a) the first stage involves checking the quality of the data – this is a complicated but simple step to understand. It is about eliminating obvious measurement errors; (b) the second and more important step is to reconcile the data and use information available from previous hours or from previous days. It is a complicated process based on a comprehensive analysis of data quite often using the model of numerical forecasts.
The idea of numerical weather forecast (NPP) was initiated by the English scientist Lewis Richardson in 1922. The calculations were done manually. It was not until 1945 that the rapid development of computer techniques meant that the NPP became operational. NPPs use the basic principles of physics describing the air flow on the rotating earth. Various forces acting on air particles such as gravity, buoyancy forces related to solar energy, air friction to the ground, effects of flow over mountains, interaction with the ocean, and many other physical processes are taken into account. The result of the numerical weather forecast are maps of basic and secondary values describing the state of the atmosphere such as pressure distribution, wind speed, temperature, precipitation, ocean wave, cloudiness.