How is weather forecast prepared?

Weather forecasting is the application of science and technology to predict the conditions of the atmosphere for a given location and time. People have attempted to predict the weather informally for millennia and formally since the 19th century. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere at a given place and using meteorology to project how the atmosphere will change. Once calculated by hand based mainly upon changes in barometric pressure, current weather conditions, and sky condition or cloud cover, weather forecasting now relies on computer-based models that take many atmospheric factors into account. Human input is still required to pick the best possible forecast model to base the forecast upon, which involves pattern recognition skills, teleconnections, knowledge of model performance, and knowledge of model biases. The inaccuracy of forecasting is due to the chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, the error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes. Hence, forecasts become less accurate as the difference between current time and the time for which the forecast is being made (the range of the forecast) increases. The use of ensembles and model consensus help narrow the error and pick the most likely outcome. There is vast variety of uses to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property. Forecasts based on temperature and precipitation are important to agriculture, and therefore to traders within commodity markets. Temperature forecasts are used by utility companies to estimate demand over coming days. On an everyday basis, many use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavy rain, snow and wind chill, forecasts can be used to plan activities around these events, and to plan ahead and survive them.Through weather forecasting, we are able to predict the state of atmosphere at a particular location. Weather forecasts are made by collecting quantitative data about the state of atmosphere at one place and applying scientific concepts pertaining to atmospheric processes to predict how the atmosphere will evolve at that place. Human beings have been predicting weather since the Stone Age. In the past, people relied on the movement and behaviors of birds and animals to predict the weather, and now, we use complex systems to analyze and predict the weather. Weather warnings are important forecasts because they help protect both life and property. For example, if we knew in advance that there is a possibility of thunderstorms /heavy snowfall/ avalanche in the region, we will try our best to stay indoors. This way, we will be able to protect ourselves. Also, weather warnings help citizens of a country to plan events for a day or even a week. Agencies have been established in every country to forecast weather conditions. In India, the Meteorological Department, under the Ministry of Earth Sciences, is responsible for predicting the weather accurately. Weather forecasting modeling is a computer program that provides meteorological information for future times at given locations. In modern forecasting models, Numerical Weather Prediction is mostly applied and this means, “a set of simplified equations used to calculate changes in atmospheric conditions”. The act of writing these equations, imposing the boundary conditions and solving them using super computers, is known as numerical modeling. Computerized numerical models are designed for different intervals which are known as global models under which we have long range forecast and medium range forecast, and regional models under which we have the short range forecast. The methods include persistence, climatologic, looking at the sky, use of barometer, now casting, use of forecasting models, analogue and ensemble forecasting. Forecasting could be applied in air traffic, severe weather alerts, marine, agriculture, utility companies, private sector and military application. Weather forecasting is a complex and challenging science that depends on the efficient interplay of weather observation, data analysis by meteorologist and computers, and rapid communication system.
Weather forecast is carried out in four steps:

1. The first step is observation. Here, standard weather instruments such as wind vane, thermometer, barometer, rain gauge and anemometer are used to observe atmospheric pressure, wind, temperature and humidity. In addition, coastal weather stations and weather ships observe the height and period of waves. Weather radars are also used to observe cloud coverage. Apart from these tools, meteorological agencies in the world depend on meteorological satellites for pictures of the Earth’s cloud formations. Data collected by these tools are then fed into a computer, which analyses them and churns out a time integration of physical equations, which is known as numerical weather prediction.

2. The next step is the plotting of weather data using numerical weather prediction on weather maps. Observations made on land and seas are plotted on the surface and sea level charts, and these charts are prepared four times a day. On the other hand, radiosonde and satellite wind observations are plotted on upper level charts, which are prepared twice a day.

3. Next, weather maps, and satellite and radar images are analyzed in depth. The data plotted on weather maps are analyzed isobarically. Here, different places with the same atmospheric pressure are connected with a line, taking into consideration the direction of the wind. Through this analysis, high and low pressure areas, cyclones, and inter-tropical convergence zones can be delineated. Also, rainfall and pressure change charts are analyzed to determine the movement of wind, distribution and intensity of rainfall and the behavior of atmospheric pressure.

4. The next step is forecasting. Once the present data is analyzed, predications and extrapolations can be made. Meteorologists compare the latest weather map with weather maps that were generated 24 to 72 hours earlier. Also, the latest weather satellite pictures are compared with earlier pictures taken 24 to 72 hours before. By comparing the latest data with older data, meteorologists are able to extrapolate and make weather predictions. These predictions, also known as forecasts, are then published in newspapers and broadcasted on the television. Weather forecasting is cumbersome, no doubt, but it is extremely useful.

Weather forecasts help people in general and in particular the farmers, pilots, sailors and even those whose livelihoods directly depend on weather conditions.
(The author a teacher by profession is posted at Government High School Brakpora Anantnag. Views are his own)

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