Weather forecasting

The weather forecast is provided by government and private weather services. The requirement to provide the meteorology as a discipline of science.

The aim of the weather forecast is the forecast of a state of the atmosphere at a particular time in a particular place or in a certain area. Here are actually not only weather phenomena that impact on the ground, meant, but looking at the entire Earth's atmosphere.

As a physical event can describe the weather by appropriate laws of nature. The basic idea of a weather forecast is to derive from an already past and the current state of the atmosphere, using the known physical laws a state in the future.

The mathematical constructs that describe these physical laws, however, are so-called non-linear equations. This means that even small changes can result in the initial state to relatively large changes in the results of the calculation ( see also: Butterfly Effect).

A distinction is essentially between a manual or synoptic weather forecast and a numerical weather prediction, which today is still a combination of both methods are used. This is due, that current numerical forecast models provide insufficient results. To account for the local climatology of meteorological stations may be connected downstream of the numerical calculations or statistical method, such as the MOS model output Statistics method nowadays.

The data on the current state of the atmosphere come from a network of ground stations that measure wind speed, temperature, air pressure and humidity and rainfall. In addition, data from radiosondes, weather satellites, commercial aircraft and weather ships are used. The problem is the irregular distribution of these observations and measurements, and the fact that relatively few stations are present in low developed countries and over the oceans.

History

The estimation of future weather development interests people for thousands of years and is the subject of intense experience and increasing research.

Attempts to predict the weather, are handed down since ancient times and are likely to go back even longer if you consider how much people - especially in agriculture - were dependent on precipitation and temperature.

So-called Lostage, known as Bauer rule - are to be regarded as an attempt to further subdivide between analogous to the seemingly always the same running times in the year, the weather- related sections. It was assumed that at Lost Agen - would take the weather and the weather, depending on the state that day, some other course which could be determined from traditions and later records - similar to a node in a decision tree.

Otto von Guericke recognized in 1660 for the first time the relationship between drop in air pressure and lift a storm. A European network of stations with simultaneous observations for the synoptic method arose soon after 1800, the North Atlantic ice - warning service but only after the Titanic sank in 1912.

In 1900 created many national weather services, developed a large-scale synoptic weather forecasts in cooperation. Since the 1950s she has been through mathematical computer models and data from meteorological satellites, improving a network of radio probes Weather and weather radar successively. Here, the relatively reliable forecast period rose at mid-latitudes of about 3 days to 4-5 days, which meant a significant improvement for many sectors of the economy, transport or construction, as well as for planning in agriculture.

Reliability

Today, a forecast for the coming week is about as reliable as it was for the next day thirty years ago. The 24- hour forecast reaches a Eintreffgenauigkeit of over 90 %. The accuracy for the next 3 days is slightly more than 75%.

However, the reliability varies greatly depending on the weather. So sometimes it is in a stable winter Hochdrucklage problem a week predict with 90 % certainty. In contrast, the prediction accuracy is often with an unstable situation thunderstorms in the summer well below 70 % for 24 hours. It must also be distinguished in the forecast quality between temperature and precipitation. Temperatures can be significantly more accurate than predicted precipitation.

In part, the weather forecast is not as reliable as the general public and various disciplines want it. This is mainly due to three causes:

• The incomplete knowledge of the actual events in the Earth's atmosphere (incomplete data or from too sparse network )
• The chaotic ( unpredictable ) share in weather
• The ( still ) insufficient accuracy of the computational models: for reasons of computing time and the large amount of data can not yet be considered with satisfactory accuracy the participating air and water masses. There are too many individual factors play a role, their interaction can not be fully analyzed to date, and also in the near future. Therefore, local factors such as mountains and their irregularly shaped slopes, effects of different irradiation by "wrong" calculated cloud cover, the vegetation (forest to farmland! ) Or rock make up so much that the accuracy for the next 4 to 7 days significantly decreases. None of the methods used today extends beyond more than twenty days in the future, so that longer forecasts, for example, seasonal weather forecasts are frivolous and are also shunned by most weather reports on television and radio.

From the existing data models can nevertheless be for different forecast ranges very reliable forecasts for weather-dependent industries create. The German Weather Service has created a prediction module for the grain moisture at fully ripe grain. This model predicts with high accuracy the grain moisture content of cereals on the basis of soil moisture, humidity and sunlight before. The forecast period extends five days in the future. The forecasts are made only in the time of summer grain harvest.

The theory of meteorology is largely resolved through the gas laws, thermodynamics and fluid dynamics, but can not calculate all air movements with sufficient accuracy by small-scale effects of up to kilometers dimensions. For example, differ over dark and light areas of several degrees on a sunny day, the temperature. The same occurs on or between water and solid ground between sunny side and shady side of a mountain ridge.

Since 1968, the quality of the DWD model predictions has increased steadily. New, bigger and improved computer weather models often led to a sharp increase in accuracy in the direction of optimum ( 1.0 ), in this example of the ground pressure predictions. From 1978, four days forecast could take two then be expected, from 1991 even seven days. 2008, a seven- day forecast was better than the two- day forecast at the beginning of the computer age in 1968. ( How good are weather forecasts? Quality testing at the DWD 2008)

Predictions by lay

To a certain degree even a layman can create a forecast for its surroundings. These can be found in bookstores concise instructions for interpretation of temperature and air pressure and for monitoring of wind and clouds - they show a lot about the horizontal and vertical air movements. Besides thermometer and barometer all you need is a good observation. But even simple weather stations for the desk plus outdoor sensor can programmed forecasts with 60 to 75 % chance to hit submit.

For the next one to three hours, you can arrive at the question of local rain, starry sky or the occurrence of frost on 80 to 90 %. Even the simplest of all forecasts - " Today is like yesterday 's " (persistence ) - applies to 50 to 70% in Central Europe. A detailed demand in weather service, by a farmer or an insurance company during thunderstorms layers can bring a higher hit rate than the uniform " TV Weather" for an entire state.

Are two forecasting tools on the Internet is of particular practical importance for the layman. The rain radar and the ensemble forecast:

• The radar provides rain for the next few hours ( so, for example, for the decision to take a walk, a short bike ride or a visit to an open-air event) often have a very reliable indication as to whether there will be rain or not.
• The ensemble forecast is good evidence for Medium-Range Weather Development and the temporal reliability of the regional weather forecast in the current weather conditions. The ensemble representation is basically a professional meteorology tool, its use can be learned fairly quickly for a few essential statements but also by the layman. For a selected location usually three ensemble representations are available: 850 hPa temperature / precipitation: In this representation can be in particular the evolution of the reliability of weather forecasts in the current weather conditions read. The value of " 850 hPa temperature" is secondary and basically for the layman usually also completely uninteresting ( it is the air temperature at about 1300 m altitude). It is essential to match the depicted different simulation runs ( different colored graphs). As long as these graphs are close together, the weather forecast is usually of high quality, as soon as the graphs diverge, the weather forecast is more of a " gambling."
• Temperature 2 m / Wind: From this representation, in particular the likely temperature development over the next few days can be read.
• Ground pressure / 500 hPa geopotential: For the uninitiated, any important notes.

Weather forecasts

Due to ever improving observational and modeling capabilities in the near future, it seems to be possible, the weather, so the weather over a long period of time to predict